When selecting a material for ventilation and aspiration systems at facilities using nuclear energy, the decision must be based on the combined assessment of regulatory requirements, operating conditions, and radiation-safety requirements. This article presents the areas where stainless steel should be used instead of galvanized sheet, the selection criteria for various NPP zones, and the regulatory framework for ventilation-system design. It also provides recommendations for organizing installation, quality control, and improving the service life of air ducts.



Regulatory Requirements for Ventilation Systems at Facilities Using Nuclear Energy

Requirements for nuclear power plant ventilation systems are governed by a set of federal rules and regulations (NP-001-15, NP-041-22) and industry standards (NP-509-21, NP-511-21).



Ventilation-system materials must have the following properties:



• corrosion resistance during long-term operation in humid environments;
• resistance to temperature fluctuations;
• resistance to alkaline and acidic decontamination solutions;
• resistance to ionizing radiation within the dose range defined for the relevant NPP zone.
• For controlled access zones (CAZ) and strict-regime zones (SRZ), additional restrictions are imposed on material porosity (to prevent the accumulation of radioactive contamination) and weldability (to ensure the integrity of sealed joints).



Quality control of metal during the manufacture and installation of ventilation systems is regulated by NP-105-18, Rules for Metal Inspection of Equipment and Pipelines of Nuclear Power Installations during Manufacture and Installation.



Galvanized Steel Air Ducts

In administrative and amenity buildings, auxiliary buildings, and non-classified rooms (class 3A/4 under the Russian NGO classification), where there is no direct exposure to aggressive substances, galvanized steel air ducts may be used. Their service life is 15-25 years, provided they are operated in a dry or moderately humid environment without chemical reagents.

Critical limitation of galvanized steel: when it comes into contact with acids, including acidic condensate, the protective zinc layer dissolves and the steel begins to rust intensively. This rules out the use of galvanized steel in areas where chemical reagents are handled and in chemical-control rooms.



Stainless Steel Air Ducts

Ventilation systems in areas with chemically aggressive media (acids, alkalis, decontamination solutions), high humidity, and areas where contaminated air that must be decontaminated may be present should use stainless steel air ducts.



The 300-series austenitic steel grades are the most widely used in the nuclear industry: AISI 304, AISI 316, and AISI 321.



Key advantages of stainless-steel air ducts:

Corrosion resistance and chemical inertness. The high chromium content (12% or more) and molybdenum content (in AISI 316) provide exceptional corrosion resistance: the surface does not oxidize when exposed to aggressive media and does not require an additional anti-corrosion coating that could impair decontaminability.



Radiation resistance. Stainless steels retain their mechanical properties over a wide range of irradiation doses. For CAZ and SRZ areas, resistance to irradiation without changes in material structure has been confirmed, which cannot be guaranteed for galvanized-sheet coatings.



Decontaminability (the property of a smooth, non-porous surface). The absence of pores and cracks on the surface of stainless steel makes it possible to remove radioactive particles easily using standard decontamination solutions in accordance with GOST R 51102-97 (decontamination factor >0.9).



Heat resistance (up to 600-900°C depending on grade). In emergency ventilation and smoke-extraction systems, ventilation ducts must remain intact during a fire within the required fire-resistance limit. Stainless steel retains its strength when heated to temperatures at which galvanizing completely loses its properties.



Long-term maintenance-free service life. High mechanical strength and rigidity (600 N/mm²) guarantee a service life of at least 50 years, provided the design sheet thickness is maintained (1.0-8.0 mm for industrial facilities). This significantly reduces the need for wall-thickness measurements, unlike degrading galvanized coatings.



Rejection of Galvanized Air Ducts at Nuclear Power Facilities

The main reasons why galvanized steel is not permitted or is not recommended for ventilation systems in safety zones 1-3A under NP-041-22 are as follows.



Limited corrosion resistance in humid and chemically aggressive environments

Decontamination solutions widely used for cleaning controlled-access rooms are acidic or alkaline. When the zinc coating comes into contact with aggressive reagents, it quickly breaks down, exposing the carbon steel, which then begins to rust actively.



Absence or instability of radiation resistance

The coating on galvanized sheet is not designed for long-term operation under ionizing radiation, so preservation of its properties throughout the entire service life cannot be guaranteed.



Low decontaminability

Even if the zinc layer remains intact, the roughness of galvanized sheet promotes the retention of radioactive particles. This may lead to elevated radiation background levels in specified rooms and require more frequent repairs.



Low heat resistance and risk of gas release during fire

The melting point of zinc (420°C) does not allow galvanized steel to be used in emergency ventilation systems, because an abrupt increase in air temperature is possible during a beyond-design-basis accident. In addition, zinc may release harmful aerosols when heated.



Recommendations for Selecting the Design of Ventilation Systems

When designing air ducts for nuclear power plants, the following principles should be followed.

Conclusions

The use of stainless steel for air ducts at nuclear power plants is not a matter of redundancy; it is a direct safety requirement.

In zones where radioactive aerosols may be released, corrosion resistance alone is not enough. The surface must be decontaminable and resistant to acids and alkalis, which is achieved only by using austenitic stainless steel (AISI 304, AISI 316L, or AISI 321) with controlled surface cleanliness. The high material cost is repaid many times over during the entire 60-year service life, because it eliminates the need to replace air ducts after only 15-20 years, as happens with galvanized systems in a moderate climate, let alone in the aggressive environment of an NPP.



The design of ventilation systems using stainless steels must be carried out in accordance with STO 95 12009-2017 (rules for concurrent works) and must include:



• radiation control of materials;

• development of a Work Execution Plan (WEP) with a section on quality control of welded joints and leak tightness;

• preparation of a ventilation-system passport with control test reports;

• admission and qualification of welders under PNAE G-7-010-89.



The metalworking process cycle (cutting, bending, and welding of austenitic stainless steels) must prevent carburization and corrosion damage to welded seams. This requires using only stainless-steel-based tools (brushes, cutting wheels) and cleaning weld areas to a bright finish, while avoiding contact with carbon steel.



A standard ventilation design must contain a schedule of stainless-steel grades indicating sheet thickness (from 0.8 to 2.0 mm for air ducts and from 2.0 to 8.0 mm for industrial assemblies) and surface-cleanliness requirements, such as a 2B finish or mirror polishing for especially clean zones.



*Compliance with industry design standards (NP-041-22, NP-509-21) and quality control at the stages of stainless rolled-stock supply, welding, and ventilation installation is the only way to guarantee the service life of the ventilation system for the entire operating life of the power unit (60 years).*



To receive a commercial proposal for the design, supply, and installation of stainless-steel ventilation systems for your facility, send a technical specification indicating the room safety class, types of aggressive media, and design service life to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, work schedule, and list of measuring and control materials under NP-105-18 will be prepared.



*This material was prepared on the basis of NP-041-22, NP-509-21, NP-511-21, NP-105-18, GOST R 51102-97, and industry requirements for ventilation systems at facilities using nuclear energy.*

Abstract. This article examines the problem of biological damage to surfaces in cleanrooms at radioactive-waste (RAW) management facilities. It shows the limitations of using stainless steel under high humidity and vibration. An engineering solution is presented: epoxy-based antibacterial putty with silver nanoparticles. Test results under GOST 9.049-91, the application technology for gypsum-board substrates, and an economic comparison with periodic replacement of sandwich panels are provided.



Regulatory Requirements and the Operating Problem

At facilities using nuclear energy (FUNE), especially plants for processing, conditioning, and storing radioactive waste, strict standards apply to air and surface cleanliness (SP 137.13330.2012 and industry rules). The traditional solution is the use of stainless steel as a corrosion-resistant material that is easy to decontaminate. However, operating practice reveals a systemic problem.



Condensate forms at vertical joints of sandwich panels under high-humidity conditions, creating an environment for microorganism growth. Studies show that even stainless steel develops biofilm over time - a stable community of bacteria and fungi attached to the surface and tolerant of ordinary disinfectants.


For facilities such as cementation and bituminization units and temporary RAW storage points, the problem is aggravated by:



• high humidity caused by technological processes;

• difficulty of regular wet cleaning in radiation-controlled zones;

• vibrations from pumping and ventilation equipment.



An additional risk factor is the possibility of growth of radiotrophic fungi on irradiated surfaces, for example mold of the Cladosporium genus. These microorganisms not only cause biocorrosion but can also damage sealing layers of coatings, leading to impairment of barrier functions.



Engineering Solution: Epoxy-Based Antibacterial Putty with Nanosilver

As an alternative to traditional finishing materials, a specialized epoxy-based antibacterial putty modified with silver nanoparticles is proposed.



Mechanism of action: silver nanoparticles release Ag+ ions, which interact with thiol groups of bacterial enzymes, disrupt the respiratory chain, and cause oxidative stress leading to cell death. This mechanism has been confirmed by laboratory studies and remains active throughout the coating's service life.



Key characteristics:



Prolonged antibacterial and fungicidal action, preventing growth of mold and fungi after repeated cleaning cycles.



Low modulus of elasticity - the coating remains elastic under dynamic loads. Unlike conventional putties, which crack under vibration, the nanosilver composition damps oscillations and preserves integrity.



Resistance to decontamination solutions, with certification under GOST R 51102-97 and GOST 26825-86.



Application Technology on Gypsum-Board Substrates

Use of antibacterial putty on gypsum-board sheets requires compliance with special conditions. The critical parameter is spraying pressure: it must not exceed atmospheric pressure (0 MPa gauge) in order to avoid destruction of the fragile gypsum-board core.



Technological cycle, step by step:



1. Deep-penetration priming - 1-2 layers with intermediate drying.



2. Joint reinforcement - taping of seams with fiberglass mesh and application of starter putty.



3. Application of the antibacterial compound - layer thickness from 0.5 to 2.0 mm depending on requirements for smoothness and mechanical strength.



4. Intermediate sanding and dedusting - removal of irregularities and dust before finishing.



5. Finish coating, if necessary - polymerization at +20°C for 24 hours.



Results of Fungal-Resistance Testing

The material passed a full cycle of industrial tests under GOST 9.049-91, the method for determining fungal resistance of paint coatings. The essence of the method is that coated specimens are infected with spores of mold fungi (Aspergillus niger, Penicillium, etc.) and held under conditions optimal for their development (temperature 28-30°C, humidity 95-98%), followed by assessment of mold-growth intensity.



Result: after six months of continuous exposure under cyclic wetting and temperature variations from +5 to +40°C, there were no signs of fungal damage. Biofilm did not form and no mold foci were present.



In addition, the coating is certified for use in the strict-regime zone (SRZ) of NPPs under GOST R 51102-97, Decontaminable Protective Polymer Coatings. It retains adhesion to the substrate after three decontamination cycles (alkaline and acidic solutions) and does not change its properties after treatment with the formulations specified in GOST 26825-86.



Economic Comparison with Alternative Solutions

Use of antibacterial putty with nanosilver provides not only microbiological cleanliness but also significant savings compared with the traditional scheme of periodic sandwich-panel replacement, which is required every 3-5 years due to biological damage.

Economic effect: in the long term, over 10 years and more, total costs are reduced by 70-80% compared with periodic panel replacement.



Application Areas and Recommendations

Epoxy-based antibacterial putty with nanosilver is recommended for use at nuclear-industry facilities where long-term biological cleanliness of surfaces is required:



safety class 4 and 5 zones under NP-041-22;



rooms for processing and conditioning low- and intermediate-level waste;



temporary RAW storage points;



cleanrooms with a regulated level of microbiological contamination.



TechAtomStroy LLC undertakes projects for anti-corrosion treatment, fire protection, and installation of specialized coatings at nuclear power plants. To calculate the cost and schedule for construction and installation works, send the facility specification and bill of quantities through the feedback form on the website.

*This material was prepared on the basis of GOST 9.049-91, GOST R 51102-97, GOST 26825-86, and SP 137.13330.2012.*

This article examines the use of busbar trunking systems for power distribution up to 1,000 V at facilities using nuclear energy. It analyzes the structural and operational advantages of busbar trunking over conventional cable lines under conditions of high-density utility routes, limited installation space, and increased requirements for reliability, fire safety, and maintainability. The article provides a classification of busbar trunking by functional purpose, technical characteristics, and the specific features of design and installation at restricted-access nuclear-industry facilities. Recommendations are given for selecting and operating busbar trunking systems.



Introduction

A busbar trunking system is a complete assembly consisting of conductors (busbars) separated by gaps and supported by insulating material, enclosed inside a pipe, tray, or similar casing. In essence, it is a factory-made rigid current conductor supplied in complete sections and used to transmit and distribute electricity in production areas and on industrial sites.



At nuclear power facilities, where power-supply systems must ensure continuous and safe operation of equipment throughout a 60-year service life, the choice of the power-distribution method becomes critical. The traditional solution - laying power cables in trays, pipes, or cable ducts - faces several limitations in the saturated engineering routes of an NPP: large bending radii of multi-core cables, the need for bulky connecting sleeves, the difficulty of adding new consumers without shutting down production, and increased energy losses.



Busbar trunking systems offer a fundamentally different solution that optimizes the use of available space, improves power-supply reliability, and reduces operating costs.



Limitations of Cable Systems under High-Density Engineering Routes

Despite their widespread use, cable power-supply systems have a number of disadvantages that are especially noticeable at facilities with high-density engineering utilities.



When power cables are laid, standardized bending radii must be observed, especially when three or four large-cross-section cables per phase are used. Bulky connecting and termination couplings are also required. In the confined conditions of NPP turbine halls, switchgear rooms, and cable trestles, this creates serious difficulties. In addition, conventional cable lines have increased fire risk: unlike busbar trunking, cable systems have a higher probability of ignition and contribute to flame spread.



Cables are also characterized by high energy losses during transmission - up to 5-7% of transmitted power. At the scale of a large industrial facility such as a nuclear power plant, this difference translates into the loss of millions of kilowatt-hours annually. The reactive impedance of cable lines is higher, which reduces the power factor and increases the load on generating equipment.



A major limitation is low maintainability and the difficulty of modernization. Adding new consumers or changing the connection scheme in densely packed cable routes is practically impossible without production stoppage and significant financial costs.



Structural and Technical Advantages of Busbar Trunking

Busbar trunking systems provide a comprehensive solution to the problems listed above. Key advantages of busbar trunking over cable systems include:



Compactness and reduced footprint. The main advantage of busbar trunking is its compact design, achieved by arranging conductors inside an enclosure. A busbar trunking system does not require much installation space, which is critical in the limited-space conditions of an NPP.



Low losses and better cooling. Due to its design and insulation quality, modern busbar trunking reduces electrical losses to 1-3%. Better cooling is achieved by the high compression density of the busbars, which are located inside a metal enclosure that dissipates heat efficiently.



Improved fire safety. Busbar trunking systems do not propagate fire, do not burn, and do not release harmful chemical substances during a fire. In the event of ignition, the busbar trunking does not create a draft effect. Many modern busbar systems maintain three-hour integrity under fire conditions (1,000°C) and provide IP68 protection for critical sections.



Flexibility and scalability. At facilities with existing electrical installations, relocating individual consumers or adding new ones is a serious financial and technical challenge. The features and advantages of the modular busbar design allow these tasks to be solved simply, quickly, and economically, because all system components can be easily disassembled and reassembled.



Durability and ease of maintenance. Under normal operating conditions, busbar trunking requires almost no maintenance, and its service life reaches 25-30 years.



Reliability. The rigid structure provides a high degree of resistance to short-circuit currents. The inductive reactance is significantly lower due to the minimum distance between conductors.



Classification of Busbar Trunking

By functional purpose, busbar trunking systems are divided into several main types.



Feeder busbar trunking is intended for constructing main lines, connecting substations on the low-voltage side, supplying distribution busbar trunking systems, and feeding individual large power receivers. Feeder busbar trunking ratings range from 630 A to 6,300 A. Main lines are built with a minimum number of joints and transmit high power over considerable distances.



Distribution busbar trunking consists of special sections with installed tap-off units to which power consumers are connected directly. Its main advantage is the ability to connect additional equipment easily without de-energizing and rebuilding the main line. Distribution busbar trunking ratings range from 100 A to 6,300 A.



Lighting busbar trunking is used to create lighting networks and connect low-power lighting fixtures at currents from 25 to 40 A. Such modules are most often used to create branched lighting routes along production lines.



Trolley busbar trunking is used to supply mobile power receivers: cranes, overhead traveling cranes, monorails, floor trolleys, and other equipment. It is produced for currents from 35 A to 1,000 A.



The design of most busbar trunking systems consists of a package of busbars tightly pressed together, insulated with polyester film, and placed inside an enclosure. The busbars are made of rectangular copper or aluminum.



Regulatory Requirements and Specific Features of Use at NPPs

Busbar trunking systems used at facilities using nuclear energy must meet increased safety requirements.



Busbar trunking equipment must have certificates of conformity and approval for use at nuclear-industry facilities. The main regulatory documents are NP-001-15, General Provisions for Ensuring the Safety of Nuclear Power Plants, the 7th edition of the Electrical Installation Code (PUE), and industry standards governing electrical installations at facilities using nuclear energy.



Chemical resistance of materials in aggressive environments is a critical requirement. Nuclear power plants and fuel-cycle enterprises operate under possible exposure to saturated vapors of nitric acid and other aggressive substances. Busbar trunking installed in such zones must have a special material composition and design that guarantee safe operation.



In zones with increased cleanliness requirements and in the containment area of an NPP, cast-resin busbar trunking with a high degree of protection - at least IP55 - and a smooth enclosure that prevents dust accumulation and allows decontamination is preferable. Fire safety of busbar trunking is also crucial: systems that do not spread combustion and do not release halogens when heated are mandatory in rooms classified as A, B, or C for explosion and fire hazard.



The classification of NPP power receivers by power-supply reliability categories according to the PUE (special category 1, category 1, and category 2) imposes requirements for redundancy and accident-free operation. Owing to high mechanical strength, lower probability of damage, and the possibility of rapid switching of sections, busbar trunking systems are a preferred solution for ensuring uninterrupted power supply to safety and control-system equipment.



Design and Installation

Switching to busbar trunking systems reduces installation time compared with cable systems and lowers the cost of electrical-installation works.



Electrical installation of busbar trunking at nuclear facilities must be carried out according to a Work Execution Plan (WEP) and in strict compliance with the requirements of the Unified Installation Standards and the Electrical Installation Code. For busbar trunking in safety-system circuits of category 1, 100% quality control of joints is mandatory: checking the tightening of bolted joints with a torque wrench, measuring contact resistance at joints with a milliohmmeter, and thermal-imaging inspection under load.



For cast-resin busbar trunking, the integrity of the cast insulation is checked before installation using a high-voltage test. Linear expansion must be taken into account: expansion sections are installed for extended lines. For rooms with increased seismicity - NPPs are built in seismic zones of up to 9 points - busbar trunking is attached to building structures through anti-seismic penetrations that allow building movements without destroying the busbar assembly.



All measurement results and concealed-work certificates are recorded in the as-built documentation and submitted to construction control.



Operation and Maintenance

Busbar trunking requires virtually no maintenance throughout its service life. The main activities are periodic thermal-imaging inspection of connection points (annually for category 1) and tightening of bolted joints in accordance with the manufacturer’s regulations (every 5-7 years).



Copper or aluminum busbars may corrode when they come into contact with acids and alkalis at nuclear-cycle enterprises; therefore, in zones with aggressive media, busbar assemblies must have a sealed enclosure of at least IP54 and an additional protective layer, such as silver plating or tinning of contact surfaces.



Conclusions

Busbar trunking systems are a technologically and economically justified alternative to cable ducts for power supply at facilities with high-density engineering utilities, including nuclear power plants and fuel-industry enterprises.



The compact design, modularity, and scalability of busbar trunking systems make it possible to use the limited space of cable rooms and turbine halls efficiently and to add new consumers quickly without shutting down production. Low energy losses (up to 1-3% versus 5-7% for cables) and better cooling provide energy efficiency and reduce operating costs. High mechanical strength, vibration resistance, non-combustibility, and resistance to aggressive media make busbar trunking a preferred solution for zones with special safety requirements, including chemically active environments and explosion- and fire-hazardous rooms.



The service life of busbar trunking reaches 25-30 years with minimal maintenance, reducing the total cost of ownership compared with cable systems that require periodic replacement and repair.



To receive a commercial proposal for the design, supply, and installation of busbar trunking systems for your facility, send a technical specification indicating capacity, redundancy scheme, zone safety class, and architectural constraints to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, an electrical-installation schedule, and a list of the required measuring and control equipment will be prepared.



*This material was prepared on the basis of the requirements of NP-001-15, the 7th edition of the Electrical Installation Code (PUE), and industry technical recommendations for power-supply systems at facilities using nuclear energy and industrial enterprises.*

This article analyzes the key aspects of performing construction and installation works at facilities using nuclear energy. It reviews the regulatory framework, including NP-041-22 and STO NOSTROY industry standards, as well as requirements for the organization of combined works, maintenance of as-built documentation, and construction supervision by Rostechnadzor. Typical violations identified during inspections are presented together with recommendations for preventing them. The material is based on practical experience in implementing projects at NPP sites.



Construction and installation works at nuclear power plants and other facilities using nuclear energy differ fundamentally from general industrial construction. In addition to standard quality and schedule requirements, a multi-level regulatory system applies here, aimed at ensuring nuclear and radiation safety at all stages - from site preparation to commissioning.



For general contractors and subcontractors specializing in construction and installation works in the nuclear industry, it is critically important to understand the procedure for developing work execution plans (PPR), the rules for carrying out combined construction and installation works at NPPs, the requirements for as-built documentation, and Rostechnadzor construction supervision procedures.



Regulatory Framework for Construction and Installation Works at NPPs

The construction of nuclear power plants is regulated by a set of federal rules and regulations (FNP), industry standards, and technical recommendations. The fundamental document for building structures is NP-041-22, "Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Facilities", which establishes requirements for categorizing structures according to their level of responsibility for radiation and nuclear safety.



With regard to the actual execution of works, the key documents are:



• STO 95 12009-2017, "Facilities Using Nuclear Energy. Construction of Nuclear Power Plants. Rules for Conducting Combined Construction and Installation Works" - regulates the procedure for work performed by several organizations simultaneously on one construction site or in one room during NPP construction.

• STO 95 12008-2017, "Facilities Using Nuclear Energy. Construction of Nuclear Power Plants. Requirements for Handling As-Built Documentation" - establishes unified rules for preparing, transferring, and storing as-built documentation.

• STO NOSTROY 2.23.83-2012, "Facilities Using Nuclear Energy. Installation of Process Pipelines at NPPs" - defines the sequence and scope of work for installing pipeline systems for VVER reactors.

• STO 95 104-2015, "Facilities Using Nuclear Energy. Development of Work Execution Plans. General Requirements" - establishes requirements for the content, development procedure, approval, and endorsement of PPRs for construction and installation works during new construction of facilities using nuclear energy.



Organization of Combined Construction and Installation Works at an NPP Site

The specifics of power-unit construction involve a large volume of combined works, where civil construction operations and installation of thermal-mechanical equipment (TME) are performed simultaneously at the same facility. The regulations distinguish between two main modes:



• "Clean" installation - performed in rooms where construction works have been completed, final finishing has been carried out, and bases have been prepared.

• Combined installation - performed while construction works are still ongoing, which requires enhanced coordination between contractors and additional safety control measures.



Practice shows that the key success factors in organizing combined construction and installation works at facilities using nuclear energy are:



1. A time-scaled network schedule with critical paths agreed upon by all participants.

2. A system of access permits and work permits for operations in confined conditions.

3. Operational quality control at each stage with the execution of inspection certificates for concealed works.

4. Geodetic support for the installation of equipment and structures.



Construction Control and Supervision: Requirements and Typical Violations

Construction control during construction and installation works at NPPs is carried out both by contractor organizations (incoming, operational, and acceptance control) and by Rostechnadzor as part of federal state construction supervision.



During inspections, Rostechnadzor assesses:



• The availability of certificates permitting work that affects the safety of capital construction facilities.

• The adequacy of the qualifications of personnel performing construction, installation, and commissioning works.

• The developer's quality assurance system (QAS) and quality assurance programs (QAP).

• Compliance of the performed works with the requirements of design documentation, technical regulations, and industry standards.



According to Rostechnadzor official reports, the most frequent violations related to nuclear power plants are:

The most typical causes of these violations are insufficient control by management and weak discipline in complying with QAP requirements at the execution level.



Specifics of Dismantling and Repair Works at Facilities Using Nuclear Energy

In addition to new construction, a significant volume of construction and installation works at facilities using nuclear energy relates to reconstruction, major repairs, and repurposing of existing buildings. Dismantling works at such facilities are regulated by SP 325.1325800.2017, "Buildings and Structures. Rules for Carrying Out Dismantling and Disposal Works", as well as by internal regulations.



Key features of dismantling works at such facilities include:



• Mandatory preliminary radiation survey of the structures to be dismantled.

• Availability of a demolition work organization plan (PORS) approved by the operating organization.

• Special requirements for handling radioactive waste (RW) generated during the work.

• Enhanced control of dust suppression and prevention of contamination spread.



Conclusions and Recommendations

Comprehensive execution of construction and installation works at NPPs requires not only technical competence from the contractor, but also deep immersion in the industry regulatory framework. The key conditions for successful project implementation are:



1. Development and approval of PPRs in accordance with STO 95 104-2015.

2. Strict compliance with NP-041-22 requirements for building structures of various safety classes.

3. Maintaining as-built documentation in accordance with STO 95 12008-2017.

4. Coordination of combined works according to the rules of STO 95 12009-2017.

5. Implementation of quality assurance programs (QAP) at all stages - from incoming inspection of materials to acceptance of completed facilities.



To request a commercial proposal for construction and installation works, dismantling, reconstruction, or major repairs at facilities using nuclear energy, please send technical specifications indicating the scope of work, the safety class of the structures, and the required deadlines to the commercial department of TechAtomStroy LLC via the feedback form on the website. Based on the data provided, a cost estimate and schedule for construction, installation, and commissioning works will be prepared.



*Prepared on the basis of NP-041-22, STO 95 12009-2017, STO 95 104-2015, NP-001-15, and official lists of typical violations published by Rostechnadzor.*

This article examines the main approaches to anti-corrosion protection of construction facilities and steel structures operated at nuclear power plants and other facilities using nuclear energy (FUNE). It analyzes the requirements of NP-041-22 for protective coatings of different safety classes, the types of paint-and-varnish materials used at NPPs, and methods for quality control of application. Recommendations are provided for selecting a coating system depending on environmental aggressiveness and radiation load.



Corrosion damage to steel structures is one of the main factors reducing the reliability and assigned service life of buildings and structures. At facilities using nuclear energy, corrosion becomes especially significant because nuclear and radiation safety depend on the integrity of load-bearing and enclosing structures.



Anti-corrosion protection of NPP steel structures must ensure preservation of the material throughout the entire design operating life, typically 50-60 years, taking into account exposure to ionizing radiation, elevated temperatures, aggressive chemical media (boric acid and decontamination solutions), and dynamic loads.



Regulatory Framework for Anti-Corrosion Protection at FUNE

The fundamental document for building structures of nuclear power plants is NP-041-22, Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Facilities. In accordance with it, all steel structures are categorized by safety class:



• Class 1 - structures whose failure leads to an accident with release of radioactive substances.

• Class 2 - structures whose failure complicates accident mitigation.

• Class 3 - structures that do not affect safety but require protection to perform their assigned functions.



Requirements for corrosion protection of steel structures are established for each class. The strictest requirements apply to coatings for classes 1 and 2: they must retain integrity during a design-basis earthquake, thermal shocks, and exposure to decontamination solutions.



Additional regulatory documents include:



• GOST 9.401-2018, Unified System of Corrosion and Ageing Protection. Paint Coatings. General Requirements and Methods for Accelerated Climatic-Resistance Testing.

• GOST R 51102-97, Decontaminable Protective Polymer Coatings. General Technical Requirements.

• GOST 26825-86, Paint Coatings for Strict-Regime Zones of NPPs.



Classification of Anti-Corrosion Protection Systems

Depending on operating conditions and the required service life, the following types of coatings are used:

High-build compounds deserve special attention: they make it possible to form a coating up to 600 microns thick in one cycle of airless spraying, reducing work duration and eliminating intercoat drying. Such materials are especially in demand during repair work performed in scheduled-maintenance windows.

Surface-Preparation Requirements

The effectiveness of anti-corrosion treatment of NPP steel structures is determined 70-80% by the quality of surface preparation. According to ISO 8501-1, for critical structures (safety class 2), a cleaning grade not lower than Sa 2.5 is required - abrasive blasting to completely remove mill scale, rust, and contamination, leaving a visually clean metal surface.

The following are additionally controlled:

• Roughness profile, usually 40-85 microns for epoxy systems.
• Presence of soluble salts (chlorides, sulfates), with a limit of no more than 20-30 mg/m² depending on project requirements.
• Degree of degreasing - absence of oils and greases is checked with a UV lamp or water-break test.

For rooms in the strict-regime zone, radiometric surface control is additionally performed before coating application.

Application Quality Control

During anti-corrosion protection works, operational control of the following parameters is mandatory:

• Wet- and dry-film thickness - step-by-step measurement on every square meter using calibrated thickness gauges (magnetometric method).
• Adhesion - by cross-cut or pull-off method in accordance with GOST 28574-2019.
• Continuity, meaning absence of pores and missed areas - using a spark holiday detector for high-build compounds.
• Color and gloss - visually against reference samples to identify repair zones.

All results are recorded in non-destructive testing reports, which form part of the as-built documentation submitted to Rostechnadzor construction control.

Features of Anti-Corrosion Protection in Zones Exposed to Radiation

For coatings operated in controlled access zones (CAZ) and strict-regime zones (SRZ), the following are additionally verified:

• Radiation resistance - the ability to retain adhesion and protective properties after accumulated radiation dose, from 10^5 to 10^6 Gy depending on location.
• Decontaminability - the ability to be washed free of radioactive contamination with standard solutions without coating destruction (under GOST R 51102-97, decontamination coefficient not lower than 0.8).
• Resistance to decontamination formulations, both alkaline and acidic, without swelling, cracking, or color change.

Organic coatings such as epoxy and polyurethane have limited radiation resistance; their use in zones with intense irradiation requires experimental confirmation of service life. In such cases, preference is given to inorganic zinc-rich compounds or hybrid liquid-glass systems.

Economic Efficiency of Selecting a Durable Anti-Corrosion System

Investment in high-quality anti-corrosion protection for steel structures of buildings and facilities pays back by reducing repair frequency and downtime. A comparison for a typical aggressive workshop with 2000 m² of structures is shown below:

In addition, durable coatings reduce radiation risks by minimizing maintenance interventions and make it possible to increase the capital class of the building in accordance with NP-041-22.

Conclusions and Recommendations

To ensure reliable and long-term anti-corrosion protection of steel structures at facilities using nuclear energy, it is recommended to:

1. At the design stage, determine the safety class of structures under NP-041-22 and the corresponding coating service life.
2. Select the coating type with regard to environmental aggressiveness, radiation load, and decontaminability requirements under GOST R 51102-97 and GOST 26825-86.
3. Ensure surface preparation to at least Sa 2.5 with control of salt cleanliness and roughness.
4. Use high-build compounds to accelerate work while maintaining the design thickness in one pass.
5. Perform a complete cycle of non-destructive testing with reports prepared for construction control.
6. For radiation-exposed zones, confirm coating resistance by decontaminability and radiation-resistance tests.

To obtain a commercial proposal for anti-corrosion protection of steel structures at your facility, including surface preparation, application of high-build epoxy, polyurea, or zinc-rich systems, quality control, and preparation of as-built documentation, send a technical specification indicating the safety class, structure area, and operating conditions to the commercial department of TechAtomStroy LLC through the feedback form on the website. A cost estimate, work schedule, and feasibility study for selecting the coating type will be prepared.

*This material was prepared on the basis of NP-041-22, GOST 9.401-2018, GOST R 51102-97, GOST 26825-86, and ISO 8501-1.*

This article examines the use of diamond cutting and diamond drilling technologies in construction, demolition, and reconstruction works at facilities using nuclear energy (FUNE). It analyzes the advantages of these methods compared with traditional methods such as jackhammers, rotary hammers, and gas cutting in terms of vibration, noise, dust generation, and preservation of surrounding structures. Typical tasks are presented: cutting openings in reinforced-concrete walls and slabs, dismantling building fragments, and drilling holes for utilities. The equipment used (wire, wall-saw, chain-saw units, and diamond core bits) and requirements for organizing work at restricted-access facilities are described.



At nuclear power plants and nuclear-industry enterprises, there is often a need to change layouts, replace equipment, modernize engineering systems, or partially dismantle structures. Traditional methods, including jackhammers, hydraulic breakers, oxy-fuel cutting, and rotary hammers, are unacceptable for several reasons: high vibration can damage neighboring critical structures, up to loss of tightness; impact loads are unacceptable near operating equipment; open flame and sparks are prohibited in zones with explosive media or hydrogen hazard; and heavy dust generation complicates decontamination and radiation control.



Diamond cutting and diamond drilling are technologies based on the use of diamond-coated tools such as segments, core bits, and wires. They make it possible to perform precise, controlled cuts and holes without impact effects, with minimal vibration, low noise, and simultaneous water cooling that suppresses dust. At facilities using nuclear energy (FUNE), these methods are widely used for building reconstruction, opening creation, demolition of large equipment, and removal of concrete-structure fragments.



Regulatory and Restricted-Access Constraints at NPPs

The use of diamond cutting technologies at facilities is governed by:



• NP-041-22 - requirements for maintaining the load-bearing capacity of structures when making openings and cutouts.

• Safety rules for working with tools (internal NPP regulations) - prohibition of impact tools in controlled-access zones and requirements for spark safety.

• Sanitary standards for vibration and noise (SanPiN) - at operating units, noise from work must not exceed 80 dBA to ensure personnel communication.

• Radiation-safety rules - organization of the work zone and control of aerosol release of radioactive dust; diamond cutting with water cooling reduces dust generation by 95-98%.



Before work begins, a work permit is issued, a work execution plan (WEP) with a diamond-cutting section is prepared, and the method of dust suppression and slurry collection is determined, including slurry containing radioactive particles when work is performed in the controlled access zone (CAZ).



Types of Work Performed by Diamond Cutting at FUNE

1. Diamond Core Drilling of Holes

• Diameter: from 8 mm to 1000 mm (standard core bits up to 200 mm, large drilling rigs up to 1000 mm).

• Depth: up to 2-3 m (with rod extension).

• Tasks: drilling holes for engineering utilities (pipes, cables, air ducts) in walls and slabs; taking concrete samples (cores) for quality control and residual-life assessment; making anchor holes for equipment fastening; ventilation, drainage, and process channels.

• Advantages: perfectly round hole without chipping (reinforcement is cut through), ability to drill at an angle, and work in confined spaces.



2. Diamond Cutting with Wall Saws

• Cut thickness: up to 500-1000 mm in one pass (blades 800-1600 mm).

• Purpose: straight-line cutting of openings in walls and slabs, cutting reinforced-concrete structures into blocks (block demolition), and removal of slab, beam, and column sections.

• Features: high cutting speed (up to 0.5-1 m²/hour of B25-B40 concrete), smooth edge, and ability to cut reinforced concrete (diamond segments cut reinforcement).



3. Diamond Wire Cutting

• Wire diameter: 8-11 mm (with diamond beads).

• Purpose: cutting massive structures of great thickness, such as walls up to 2-3 m, foundations, and shells; dismantling large equipment by cutting frames, housings, and thick-walled pipes.

• Advantages: unlimited cutting depth, ability to cut along a curved contour (for example, removing a wall fragment of complex shape), and low vibration.



4. Chasing and Chain Cutting

• Narrow slots: width 30-50 mm, depth up to 400 mm.

• Tasks: chases for wiring, pipes, safety systems, and installation of flexible cable ducts.



Organization of Diamond-Cutting Works at Restricted-Access Facilities

Because works are often performed at operating power units or in zones under partial radiation control, the process is strictly regulated:



1. Preparatory stage: radiation survey of the cutting zone (for CAZ), marking, installation of barriers, supply of water and electricity (3x380 V, 16-32 A). For wire and wall-saw equipment, a cooling system with water supply up to 20 L/min is required.

2. Equipment fastening: drilling rigs and cutters are fixed to concrete with anchors (with pull-out verification) or vacuum plates to prevent displacement due to vibration.

3. Cutting process: continuous monitoring of current, feed rate, and water flow. In the CAZ, spent water (slurry) is collected and sent for analysis as potential radioactive waste.

4. Removal of the cut fragment: winches, jacks, and cranes are used for dismantling large blocks, with preliminary calculation of block weight. The opening edges are cleaned and the reinforcement is checked for preservation of load-bearing capacity.

5. Completion: water pumping, packaging of slurry in containers, and cleanliness control of the surface before sealing the opening, if necessary.



Advantages of Diamond Cutting over Traditional Methods at NPPs

Examples of Diamond-Cutting Applications at FUNE

• Creating a technological opening in a reactor-hall wall: thickness 1 m, B40 concrete, three-row reinforcement. Diamond wire cutting with water cooling is used. The opening is completed in two shifts without vibration, and reinforcement of adjacent areas is not required.



• Drilling 200 holes for pipes of an emergency cooldown system: diameter 150 mm, depth 500 mm, reinforced concrete. With diamond core bits, one hole takes 15-20 minutes versus 1.5 hours using a rotary hammer with a conventional concrete core bit (without diamonds).



• Dismantling the lining of a spent-fuel pool: cutting acid-resistant brick and concrete base with diamond blades with a high service life (polishing diamond segments). Dust and slurry are collected in a closed-loop system with purification, preventing spread of radioactive particles.



Quality Control and Safety

• Control of cutting parameters: deviation from the cutting line must not exceed 5 mm over 10 m of length, and there must be no uncut sections.

• Inspection of cutting tools: diamond segments are checked for wear; wire is replaced after 30-50 m² of cutting depending on concrete class.

• Radiation control: in strict-regime zones, every core and all slurry are checked, and equipment is decontaminated after work.

• Electrical safety: equipment is connected through an RCD (30 mA); water cooling prevents water from entering electronics (built-in IP54 systems).



Conclusions and Recommendations

The use of diamond cutting and drilling at facilities using nuclear energy is technically justified and economically efficient for demolition, reconstruction, and modernization tasks. It is recommended to:



1. Use only diamond cutting for all openings in load-bearing structures (walls, slabs) at NPPs, without transferring impact loads to the structures.

2. When dismantling large fragments (blocks), use wire cutting with selection of wire diameter depending on reinforcement and concrete strength.

3. For drilling holes for utilities and anchoring, use diamond drilling rigs fixed to the surface by vacuum or anchors to ensure accuracy.

4. Mandatory design of water cooling and slurry collection in the CAZ, followed by disposal as potentially radioactive material.

5. Include in the as-built documentation reports on opening-geometry control and certificates of inspection for hidden works (reinforcement, strength of opening edges).



To obtain a commercial proposal for diamond cutting and drilling at your facility, including drilling holes for utilities, creating openings, block demolition by wire cutting, and collection and disposal of slurry, send a technical specification indicating material type, thickness and reinforcement, required accuracy, and room safety class to the commercial department of TechAtomStroy LLC through the feedback form on the website. A cost and schedule calculation will be prepared with the restricted-access requirements of the site taken into account.



*This material was prepared on the basis of NP-041-22, Rostechnadzor requirements for reconstruction at operating NPPs, and safety standards for diamond cutting (EN 13236, GOST R IEC standards).*

This article examines the purpose and design of filter-fan modules (FFMs) as key elements of air cleanliness systems in critical areas. It analyzes regulatory requirements for equipment used in the nuclear industry, including NP-041-22, ASME AG-1 standards, and the NP-509-21 fire safety rules. It also reviews TROX solutions intended for cleanrooms and nuclear energy facilities: FFT-TC Fan Filter Unit modules, MFPCR replacement filters, and the X-CUBE CROFCU modular central air-handling unit. Technical features, selection criteria, and installation requirements for controlled-access facilities are provided.



Introduction. The Role of Filter-Fan Modules at Nuclear Power Plant Facilities

A filter-fan module (FFM) is a compact device designed to create local zones with specified air cleanliness levels. As a rule, it consists of a plenum chamber, a high-efficiency fan, a HEPA filter (High Efficiency Particulate Air) or ULPA filter (Ultra Low Penetration Air), a diffuser, and a control unit. Such modules are widely used to organize laminar airflows in cleanrooms, operating rooms, pharmaceutical manufacturing, and the nuclear industry.



At nuclear energy facilities, FFMs are used in the following critical systems:



• ventilation of glove boxes and chambers for handling radioactive materials;

• emergency filtered venting systems (Filtered Containment Venting System, FCVS);

• supply-air units for clean zones, for example areas where fuel assemblies are repaired;

• systems for maintaining the required cleanliness class in rooms with precision equipment.



The key distinguishing feature of FFM requirements at nuclear power plants is increased reliability, radiation resistance of materials, minimal outgassing, and the possibility of decontamination.



Regulatory Framework

Filtration and ventilation system equipment for the nuclear industry must comply with a set of federal rules and regulations as well as international standards.



• NP-041-22, “Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Facilities,” establishes room safety classes, which directly determine requirements for ventilation equipment.

• The rules for the design and operation of safety-related ventilation systems at nuclear power plants (new federal rules and regulations updated in 2023) apply to both designed and operating NPP ventilation systems.

• NP-509-21 and NP-511-21 establish requirements for fire safety systems, limiting the use of certain materials and methods of laying air ducts.

• ASME AG-1, “Code on Nuclear Air and Gas Treatment,” is the key international standard for components of nuclear power plant air treatment systems. It establishes requirements for the design, efficiency, qualification, and testing of high-efficiency filters for nuclear facilities.



Key Technical Requirements for FFMs in the Nuclear Industry

Equipment selection must take into account the following indicators, confirmed by testing.



Filtration Class

Safety-related systems use high-efficiency filters (HEPA) and ultra-high-efficiency filters (ULPA). Classes H14, U15, and U16 under EN 1822 retain up to 99.995–99.9999% of particles sized 0.1–0.3 μm. Nuclear installations also use filters qualified under ASME AG-1, Section FC, for axial-flow HEPA filters, which require additional reliability testing such as earthquake simulation and exposure to steam and humidity.



Tightness and Design

Filters must be equipped with a continuous flange seal or a fluid seal to prevent air bypass between the cassette and the housing. The design of the filter elements must be non-combustible and must maintain integrity under dynamic loads, including seismic impact.



Radiation Resistance

Materials used in housings and seals must not degrade under ionizing radiation. Resistance to doses of up to 10⁶ Gy is usually required. Components operated in strict-regime areas require additional confirmation of decontaminability and minimal outgassing in order to prevent contamination of technological processes.



Energy Efficiency

NPP ventilation systems are major electricity consumers. Modern fans using EC technology (electronically commutated motors) provide capacity control and low power consumption.



TROX Solutions for Filtration and Ventilation Systems

The German TROX Group supplies comprehensive solutions for ventilation, air conditioning, and air filtration. TROX products are represented in almost every country in the world, and in China the company is an accredited supplier of heating, ventilation, and air-conditioning system components for the nuclear industry of the People’s Republic of China.



Fan Filter Unit Modules (FFT-TC)

The FFT-TC series consists of ready-to-install filter-fan modules for cleanrooms. They create a top-down laminar airflow, are installed in suspended ceilings, and form a self-supporting structure.



Main technical features:



• oil-free fan with adjustable rotation speed;

• absolute filter with a fluid seal (gel seal), class H14;

• low noise and vibration levels;

• galvanized steel housing with an anti-corrosion coating.



MFPCR Filter Elements for the Nuclear Industry

The Mini Pleat Filter Panels MFPCR line consists of replacement cartridges for final filtration of supply and exhaust air. The manufacturer explicitly states their suitability for use in nuclear power applications.



Key characteristics:



• filter medium: moisture-resistant glass fiber media with thermoplastic pleat separators;

• anodized aluminum frame;

• guaranteed efficiency: H14-class HEPA filters supplied with ALC and ALG frames undergo 100% leak-detector inspection with automatic surface scanning (scan test);

• flexible adjustment of pleat geometry to minimize pressure drop.



X-CUBE CROFCU Modular Air-Handling Units

For comprehensive air preparation in cleanrooms in the nuclear industry, X-CUBE CROFCU modular central air-handling units are used. The system combines ventilation, filtration, cooling/heating, and supports cleanliness classes up to ISO 4, corresponding to Russian Class 10 under GOST R ISO 14644. The equipment is fitted with energy-efficient EC fans and is suitable for Category A/B areas (clean zones).



Installation and Quality Control Features

Work to introduce filter-fan modules at nuclear power plants must be carried out in strict compliance with work execution plans (WEPs) and the requirements of Rosatom’s unified access permit system.



Installation in Laminar Ceilings

FFT-TC modules are installed in special grid panels (tiles) of a suspended ceiling. The permissible height difference during installation must not exceed 1.0 mm per meter. Adjacent modules are joined into a frame to form a monolithic surface, preventing the bypass of unfiltered air.



Quality Control

Acceptance testing at the site must confirm the following parameters:



• filtration efficiency and continuity of the filter medium, using the scanning method for filters of class H14 and above;

• pressure drop across a clean filter and after dust loading, compared with passport data;

• airflow rate and flow velocity in the working area;

• noise level and aerosol particle concentration (0.5 μm) in accordance with ISO 14644;

• maximum pressure drop across the filter under a load of 250 Pa and higher.



For nuclear installations, qualification under ASME AG-1 is also required for air treatment system components, including leak-tightness testing after deformation (upset conditions simulation).



Special Requirements for Filter Replacement and Disposal

Spent filter-fan modules that have operated in areas with radioactive or toxic environments must be handled as solid radioactive waste (SRW). The system design must provide technical means for replacing filters without compromising circuit tightness, for example transfer containers using the “bag-in-bag” technology.



Conclusions and Recommendations

The use of certified filter-fan modules ensures the quality and reliability of cleanroom ventilation at nuclear industry facilities. TROX equipment that complies with EN 1822 and is applicable to nuclear infrastructure makes it possible to provide:



• cleanliness classes from H13 to U16, depending on the task;

• fluid sealing (gel) to ensure guaranteed tightness;

• the possibility of integration into laminar ceilings (FFT-TC modules);

• low power consumption and reduced operating costs.



Recommendations for Selecting FFMs:



1. The filter class must correspond to the design cleanliness category of the room: H14 for clean zones and U15–U16 for the most critical zones.



2. The housing and seals must be made of materials with reduced gas release and must allow decontamination, for example an anodized aluminum housing and high-hardness rubber seals.



3. For Category A rooms (clean zones), compliance with microbiological cleanliness standards must be confirmed, including verification that there is no stagnant water or hidden cavities.



4. The FFM installation design for an NPP must include a section on handling spent filters as potential radioactive waste.



To receive a commercial proposal for the design, supply, and installation of TROX filter-fan modules, including preparation of a justification for Rostechnadzor construction supervision, send the technical assignment to TechAtomStroy LLC’s commercial department via the feedback form on the website, specifying the cleanliness class, air capacity, and decontamination requirements.



*This material has been prepared using TROX data as well as the requirements of NP-041-22, ASME AG-1, and the rules for operating NPP ventilation systems.*

This article examines the objectives and methods of fireproofing works for buildings and structures of nuclear power plants. It analyzes the requirements of NP-509, NP-511, and other regulatory documents for the fire resistance of building structures, limitation of fire spread, and use of non-combustible materials. It describes methods for improving the fire resistance of steel and concrete structures, replacing fire-hazardous materials, installing fire barriers, and applying fireproof coatings. Recommendations are provided for an integrated approach to fire protection at facilities using nuclear energy (FUNE).



Ensuring fire safety at nuclear power facilities is one of the priority areas, because fire can lead to failure of safety systems, loss of reactor control, and radiological consequences. Unlike general industrial buildings, NPPs are subject to special requirements: not only fire-resistance ratings of structures (R, REI), but also limitations on flame spread, smoke generation, toxicity of combustion products, and resistance of fireproofing to decontamination and ionizing radiation.



Fireproofing works at facilities using nuclear energy include treatment of steel and reinforced-concrete structures with fireproofing compounds, replacement of combustible materials with non-combustible materials, installation of fire partitions and doors, sealing of cable penetrations, and modernization of existing buildings to improve their fire safety.



Regulatory Framework for Fireproofing at NPPs

The main documents governing fireproofing requirements at facilities using nuclear energy are:

• NP-509-21, Fire Safety Rules for Nuclear Power Plants, establishes the mandatory use of non-combustible and flame-retardant materials and the required fire-resistance limits for structures depending on the safety class of the room.

• NP-511-21, Requirements for Fire Protection Systems of Nuclear Power Plants, regulates passive and active fire protection systems, including fireproofing of building structures.

• Federal Law No. 123-FZ, Technical Regulations on Fire Safety Requirements, applies to the classification of construction materials by combustibility (G1-G4, NG) and structural fire hazard.

• STO 95 12009-2017 (rules for concurrent works) also contains sections on fire safety during construction and installation works.



Classification of Construction Materials by Combustibility

For NPP facilities, NG-class (non-combustible) or G1-class (low-combustibility) materials with low smoke generation and no halogen release are preferred. Replacement of fire-hazardous materials (wood, foam plastic, unmodified bitumen compounds) with non-combustible or fire-protected materials is mandatory during reconstruction and overhaul.

Methods of Fireproofing Works at NPPs

1. Fireproofing of Steel Structures

Steel columns, beams, trusses, and bracing in NPP buildings rapidly lose load-bearing capacity during a fire (at 500-600°C the yield strength of steel is reduced by half). The following are used to increase the fire-resistance limit to the required R90, R120, or R180:



• Thin-layer intumescent coatings (which expand when heated to 150-250°C) with a dry-film thickness of 0.5-3 mm, providing R60-R150. These compounds are based on polyurethane, epoxy resin, or acrylic. Radiation-resistance verification is required for zones with doses above 10^5 Gy.

• Thick-layer cement and perlite plasters (15-40 mm thick) provide R90-R240, are non-combustible and radiation-resistant, but are heavy and increase the section thickness.

• Fireproof boards and linings (vermiculite, gypsum-fiber boards, basalt mats) are used for hard-to-reach areas and where the appearance must be preserved.

• Hybrid liquid-glass coatings combine the properties of inorganic and organic systems and have pendulum moisture release, which helps prevent hydrogen explosion.



Before applying the coating, steel structures are cleaned to Sa 2.5 (abrasive blasting) and primed with a compatible primer. Thickness is controlled with a magnetic thickness gauge, and adhesion is checked by cross-cut or pull-off testing.



2. Fireproofing of Reinforced-Concrete Structures

The fire resistance of reinforced concrete depends on the thickness of the protective concrete cover over the reinforcement. If the cover is insufficient (less than 20 mm), concrete cracks and spalls when heated, and the reinforcement is exposed and loses strength. Fireproofing works include:



• Increasing the protective cover (shotcreting, plastering with vermiculite-cement mortar).

• Fireproof paints for concrete (intumescent compounds, 0.5-2 mm thick).

• Replacement of damaged concrete with heat-resistant concrete (aluminate cement) during repair.



3. Replacement of Fire-Hazardous Materials and Structures

When reconstructing existing buildings built before modern standards were introduced, the following must be replaced:



• Wooden rafters and floors with steel or reinforced-concrete structures with fireproofing.

• Expanded-polystyrene insulation (G3-G4) with NG-class basalt wool.

• Unprotected cable routes with NG-LS (low-smoke) coated cables and firestop penetrations.

• Fire-hazardous wall and ceiling finishes (PVC panels, wood-fiber boards) with non-combustible or G1 materials.



Dismantling of old materials and installation of new ones are carried out under a Work Execution Plan agreed with the fire-safety department.



4. Installation of Fire Barriers

In addition to fireproofing of load-bearing structures, fire barriers are installed:



• Type 1-2 fire walls and partitions (REI 150, REI 120) made of brick or blocks and filled with non-combustible insulation.

• Fire doors and hatches (EI 60, EI 90) with automatic closers and seals.

• Fire-protected penetrations for pipes, cables, and air ducts through walls and floors (fire-resistant collars, embeds with mineral wool, sealants).



Quality Control of Fireproofing Works

Acceptance of fireproof coatings and structures at NPPs is carried out according to the following parameters:



• Coating thickness (not less than the design value; measurements at 5 points per 1 m²).

• Continuity (absence of gaps, cracks, and delamination, checked visually and by tapping).

• Adhesion to the substrate (cross-cut or pull-off method, not less than 1.0 MPa for epoxy compounds).

• Fire tests (for new materials, a report from an accredited laboratory; for serially used materials, a fire-safety certificate and product passport).

• Radiation resistance (when used in a controlled access zone, an irradiation-dose test report).



All results are documented in concealed-work inspection certificates (for coatings later covered by finishing layers) or acceptance-control certificates.



Conclusions and Recommendations

Integrated fire protection of NPP facilities must include not only treatment of steel structures but also replacement of combustible materials, installation of barriers, and sealing of penetrations. It is recommended to:



1. At the design stage of new construction, specify non-combustible materials (NG or G1 class) and structural solutions with the required fire-resistance limit under NP-509.



2. For existing buildings, conduct an audit of fire-hazardous materials and develop a replacement program with phased fireproofing of the most important load-bearing structures.



3. For safety class 1-2 steel structures, use fireproofing with a service life of at least 50 years (inorganic linings or hybrid liquid-glass coatings).



4. Ensure quality control at all stages: incoming inspection of materials, operational control of thickness and adhesion, and acceptance testing.



5. For strict-regime zones, additionally verify the decontaminability and radiation resistance of fireproofing compounds.



To obtain a commercial proposal for fireproofing works (application of intumescent coatings, installation of fire barriers, replacement of fire-hazardous materials with non-combustible ones, and sealing of cable penetrations) at your facility, send a technical specification indicating the type of structures, required fire-resistance limits (R, REI), room safety class, and operating conditions to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, work schedule, and optimal fireproofing systems selected with NP-509 requirements in mind will be prepared.



*This material was prepared on the basis of NP-509-21, NP-511-21, Federal Law No. 123-FZ, and GOST R 53293-2009.*

This article examines the specific features of installing floors, screeds, and lining coatings in buildings and structures of nuclear power plants and other facilities using nuclear energy. It analyzes the requirements of NP-041-22 and industry standards for substrate flatness, strength, chemical resistance, decontaminability, and fire resistance. It presents types of screeds (cement-sand, polymer, anhydrite), types of linings (acid-resistant brick, polymer self-leveling floors, tile), technological stages of work, and quality-control methods.



The floors of industrial and special-purpose rooms at nuclear power plants operate under high mechanical loads, exposure to aggressive liquids (boric acid, oils, decontamination solutions), elevated temperatures, and, in controlled access zones, radiation background and the need for regular decontamination. Incorrect selection of the floor structure, screed, or finishing coating leads to premature deterioration, accumulation of contamination, increased dose loads on personnel, and unscheduled repairs.



Flooring, screed, and lining works at facilities using nuclear energy must ensure the design flatness, load-bearing capacity, chemical resistance, and maintainability for the entire service life of the building, typically 50-60 years. This article discusses the main types of screeds and linings used at NPPs and the requirements for their installation.



Regulatory Framework

• NP-041-22, Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Structures, classifies floors by safety class depending on the room and establishes requirements for coating resistance.

• SP 29.13330.2011, Floors (updated version of SNiP 2.03.13-88), is the main document for the design and installation of floors in industrial and civil buildings.

• GOST R 51102-97 sets requirements for the decontaminability of polymer floor coatings in strict-regime zones.

• GOST 26825-86 covers the resistance of paint-and-varnish and polymer coatings, including floors, to decontamination solutions.

• Departmental Construction Standards for NPPs regulate the installation of linings made of acid-resistant materials in rooms with aggressive media.



Types of Screeds Used at Facilities Using Nuclear Energy

A screed is the base for the final floor covering. In the nuclear industry, the following types of screeds are used depending on the room and the subsequent coating.



1. Cement-Sand Screed (Traditional)

• Composition: M400-500 cement, sand with a fraction up to 2.5 mm, water, and plasticizers.

• Thickness: 40-80 mm over a concrete slab / 80-100 mm over thermal or acoustic insulation.

• Application: under subsequent tile laying, acid-resistant brick lining, and polymer self-leveling floors as a leveling layer.

• Limitations: long curing period (28 days to full strength) and high shrinkage if the water-cement ratio is violated.



2. Polymer Screed (Self-Leveling Floor as a Base)

• Composition: epoxy or polyurethane compounds with quartz sand.

• Thickness: 3-10 mm as a finishing coating or up to 25 mm as a base screed.

• Application: in clean rooms, strict-regime zones, and rooms with decontaminability requirements.

• Advantages: fast curing (1-3 days), high chemical resistance, seamless surface, and easy cleaning.



3. Anhydrite (Gypsum) Screed

• Composition: gypsum binder with additives.

• Application: for dry rooms in auxiliary buildings (administrative and amenity buildings); it is rarely used at NPPs due to low water resistance and is used only where spills are guaranteed to be absent.

Conclusion on screeds: for critical NPP rooms such as reactor halls, decontamination rooms, pump rooms, and spent-fuel pools, a reinforced cement-sand screed (with fiber or mesh) followed by acid-resistant brick lining or a self-leveling polymer coating is preferable. For auxiliary zones and corridors, a polymer screed may be used as an independent coating.



Lining Works

Lining is the installation of a protective layer made of piece materials (acid-resistant brick or ceramic tile) or monolithic compounds (polymer concrete) to protect the base from chemically aggressive media and mechanical impacts.



Acid-Resistant Lining (Brick and Tile)

• Material: acid-resistant brick grades KU and KS; acid-resistant tile under GOST 961-2017.

• Mortar: acid-resistant grout based on water glass (potassium or sodium) with acid-resistant filler (andesite, quartz).

• Application area: rooms with frequent spills of boric acid, alkalis, and oils - battery rooms, decontamination rooms, chemical laboratories, and radioactive-waste handling rooms.

• Technology:



1. Waterproofing of the base (coating-type bitumen or polymer waterproofing).

2. Laying acid-resistant brick on mortar (joint thickness 3-5 mm).

3. Pointing the joints with the same acid-resistant mortar.

4. Drying at a temperature not lower than +15°C for 7-14 days.

5. Checking coating continuity by tapping and acid resistance by a drop test.



Polymer Self-Leveling Floors (Epoxy, Polyurethane)

• Thickness: 2-6 mm for thin-layer systems and up to 12 mm for quartz-filled systems.

• Application: clean rooms, corridors, operator rooms, and medical stations where frequent acid spills are absent.

• Advantages: seamless surface, easy decontamination, possibility of thin-layer application, and high adhesion to concrete.

• Limitations: they are damaged by spills of concentrated acids and point impacts from heavy equipment.



Rubber and Polymer-Cement Linings

• Rubber sheets (adhesive installation) are used for floors in electrical switchboard rooms and in battery rooms with electrolyte (acid-resistant rubber).

• Polymer-cement coatings are 10-20 mm thick and are used in zones of moderate aggressiveness, such as wet workshops.



Requirements for Base Preparation

The quality of the lining and the durability of the floor depend on base preparation. The following are mandatory for all types of coatings:



• Base strength: compressive strength of at least 20 MPa for cement screeds, with no delamination or peeling.

• Flatness: the gap under a 2-meter straightedge must not exceed 2-4 mm, depending on the type of final coating.

• Moisture content: not more than 4% for cement screeds and not more than 3% for epoxy self-leveling floors.

• Cleanliness: no oil stains, dust, formwork residues, or cement laitance; milling or grinding is mandatory.

• Priming: with a primer compatible with the floor material, either epoxy or polyurethane.



For rooms in strict-regime zones, radiometric monitoring of the base is additionally performed before the final coating is applied.



Technological Cycle for Installing a Floor with Lining (Example: Acid-Resistant Brick in a Chemical Laboratory)

1. Placement of concrete blinding layer (B15-B25), 150-200 mm thick.

2. Cement-sand screed (M200), 40-50 mm thick, with steel mesh (Ø4 mm, 100 x 100 mm grid).

3. Waterproofing (bitumen-polymer mastic in two layers), mandatory for rooms with aggressive liquids.

4. Priming the surface before applying acid-resistant mortar (water glass + sand).

5. Laying acid-resistant brick on mortar with vibration rubbing-in.

6. Joint pointing (filling with acid-resistant grout).

7. Curing under dry conditions at t = 20±5°C for 14 days.

8. Quality control: tapping, drop test with 5% sulfuric acid, and, if necessary, pull-off adhesion measurement.



Quality Control during Screed and Lining Installation

• Incoming inspection of materials: passports, certificates (brick, mortar, primers), and production dates.

• Operational control: base moisture and flatness, compliance with temperature and drying periods, joint thickness, and absence of voids (tapping).

• Acceptance control: certificates for inspection of concealed works (waterproofing, reinforcement), adhesion-strength test reports (for self-leveling floors, pull-off samples), and a chemical-resistance certificate (for acid-resistant brick lining, a test certificate for exposure to decontamination formulations).



Conclusions and Recommendations

When selecting the type of floor, screed, and lining for nuclear power plant rooms, the following factors should be considered:



1. The safety class of the room under NP-041-22. For zones where aggressive media may be spilled, lining with acid-resistant brick or a polymer-cement compound is mandatory.



2. Decontaminability requirements under GOST R 51102-97. For controlled access zones, smooth seamless floors (self-leveling polymer floors) with a decontamination factor of at least 0.8 are preferable.



3. Mechanical loads. In areas where heavy equipment is moved, such as transport corridors and pump rooms, brick lining or steel sheets are recommended; in operator rooms and clean rooms, an epoxy self-leveling floor is recommended.



4. Temperature conditions. For hot workshops (up to 80°C), heat-resistant concretes and polymers with thermal expansion compatible with the base are used.



High-quality flooring, screed, and lining works ensure the required building service life, safe operation, and savings on repairs throughout the entire operating period.



To receive a commercial proposal for flooring, screed, and lining works at your facility, including base-structure design, selection of acid-resistant lining or polymer coating, a full scope of works, and quality control, send a technical specification indicating the room type, safety class, environmental aggressiveness, and planned loads to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost and schedule estimate will be prepared, and the optimal floor structure for your facility will be selected.



*This material was prepared on the basis of NP-041-22, SP 29.13330.2011, GOST R 51102-97, and industry standards for lining works at NPPs.*

This article examines amendments to NP-001-15, General Provisions for Ensuring the Safety of Nuclear Power Plants, which entered into force in 2025, and their impact on requirements for maintainability of building structures. A comparative analysis is provided of the durability of different types of anti-corrosion and fire-protective coatings, including polyurea, epoxy systems, polyurethane compounds, and standard enamels. The economic feasibility of using coatings with a 30-50 year service life to increase the capital class and reduce operating costs is demonstrated. A payback calculation is provided using a deaerator trestle as an example.



Regulatory Changes and Updated Maintainability Requirements

In 2025, Rostechnadzor approved amendments to NP-001-15, General Provisions for Ensuring the Safety of Nuclear Power Plants. The document entered into force on September 29 and introduced changes to the regulatory framework for design, construction, and operation of facilities using nuclear energy (FUNE). The key innovation was stricter requirements for maintainability of NPP buildings and structures as one of the factors affecting safety and assigned service life.



Maintainability in the nuclear industry is defined as the ability of a structure to retain operability during maintenance and repair, taking into account restrictions related to radiation conditions and personnel access. For steel structures with protective coatings, this requirement includes:



• minimum frequency of protective-layer restoration;

• compatibility of repair compounds with the original coating;

• ability to perform repairs within compressed timeframes, during scheduled preventive maintenance outages.



Relationship Between Maintainability and Capital Class

The capital class of an NPP building or structure is determined at the design stage and depends on the calculated service life, operating conditions, and the durability and maintainability of the structures. According to NP-010-16, the operating organization is required to develop a service-life management program for equipment, pipelines, and building structures. When service life is extended, justification of continued operation is required, for example in accordance with RB-167-20, Recommendations for Justifying the Residual Life of Building Structures at Facilities Using Nuclear Energy.



Selecting a coating with a confirmed long service life makes it possible to:



• assign the structure to a higher capital class;



• reduce the number of unscheduled repairs;



• lower maintenance costs over the life cycle.



Economic Consequences of Power-Unit Shutdown

A power-unit shutdown for repair is accompanied by:



1. direct losses from underproduction of electricity, amounting to millions of rubles per hour at current tariffs;

2. costs of reactor cooldown, removal of fuel assemblies, and coolant drainage - procedures that take weeks;

3. additional dose loads on personnel.



For this reason, designers and operating organizations are interested in maximizing the repair interval of all building elements, including protective coatings on steel structures.



Comparative Analysis of Coating Durability

Strategy for Selecting a Coating with Maintainability in Mind

When choosing a coating type for a specific NPP zone, the following principles are recommended:



Polyurea coatings (50 years) - for zones where repair is extremely difficult or associated with radiation risks, such as spent-fuel pools, deaerator trestles, and rooms with safety-system equipment. They eliminate the need for restoration during the entire life cycle of the unit.



Epoxy coatings (30 years) - for most industrial zones where access for repair is possible within 2-3 scheduled preventive maintenance outages.



Standard enamels (3-5 years) - only for auxiliary and temporary structures that do not affect safety.



Economic-Efficiency Calculation (Using a Deaerator Trestle as an Example)

Initial data: deaerator-trestle zone, steel-structure area - 2000 m², operating conditions - high humidity and limited access for repair.

Additional advantages of the polyurea coating:



• no need to stop equipment for inter-repair restoration;

• possibility of local touch-up without taking the structure out of service;

• reduction of dose loads on maintenance personnel.



Conclusions

The introduction of amendments to NP-001-15 increases the importance of maintainability of building structures when justifying the capital class of NPP buildings. The use of coatings with a 30-50 year service life, such as polyurea and modern epoxy systems, makes it possible to:



• increase the capital class without changing load-bearing structures;

• reduce life-cycle operating costs by 60-70%;

• minimize the risks of unscheduled power-unit shutdowns.



Investments in durable protective coatings should be considered not as an expense item, but as a means of ensuring continuous safe operation and reducing total cost of ownership.



To obtain a commercial proposal for applying polyurea, epoxy, and other durable coatings at facilities using nuclear energy, send a technical specification indicating the structure area, required protection class, and operating conditions to the commercial department of TechAtomStroy LLC through the feedback form on the website. Based on the submitted data, a cost estimate, construction-and-installation work schedule, and feasibility study for selecting the coating type will be prepared.

Abstract. The use of a new paint-and-varnish or protective coating that is not included in industry lists at facilities using nuclear energy (FUNE) requires completion of an established procedure for documented confirmation of conformity. This article presents a sequential list of seven documents required for approval of the material by Rostechnadzor construction control. It examines requirements for the product passport, qualification test reports, the conclusion of the Lead Materials Science Organization (LMSO), the certificate of conformity, and inclusion in the Consolidated List.



General Principle

When accepting new materials at an NPP, construction control follows the principle of 'presumption of non-applicability': if a material is not included in approved industry lists of standardization documents, it is considered not approved for use. The legitimization process is built as the sequential formation of an evidence base, from the manufacturer's documentation to a legally significant approval by Rostechnadzor. The seven mandatory elements of this system are listed below.



1. Product Passport (Initial Quality Requirements)

Purpose: to record the basic characteristics of the material and confirm its compliance with technical specifications (TU).



Content: the passport must include information about the intended use, chemical composition, physical and mechanical properties (yield strength, modulus of elasticity, corrosion resistance), as well as reports of initial factory tests. A reference to duly approved technical specifications is mandatory.



Key parameters checked by the inspector:



• Safety class of the building structure under NP-041-22.



• List of aggressive media with which the material will come into contact.



• Operating-temperature range (for NPPs it is wider than for general industrial equivalents).



• For coatings in strict-regime zones, compliance with GOST 26825-86 (requirements for chemical resistance and appearance after exposure).



2. Guideline Document (Assessment of Impact on FUNE)

Purpose: documented justification that the use of the coating does not compromise the external or internal safety of the facility using nuclear energy.



Content: the document is prepared by the lead materials science organization or another accredited organization and contains calculations and justifications in the terminology used in mechanical engineering for nuclear power plants. It relies on industry federal rules and regulations (FNiP), which impose stricter requirements for fire, radiation, and mechanical resistance than general-construction GOST standards.



3. Qualification Test Report (Testing under PNAE G-7-010-89 and Related Standards)

Purpose: to confirm the coating's resistance to impacts simulating actual NPP operating conditions.



Content: for steel structures, the basic document is PNAE G-7-010-89 or its updated versions (NP-105-18). For paint-and-varnish coatings, analogous test reports are used to verify compliance with:



• GOST R 51102-97 (decontaminability of coatings);



• GOST 26825-86 (resistance to decontamination solutions);



• GOST 27708-88 (resistance to decontamination formulations).



Mandatory types of testing:



Resistance to aggressive liquid media: 5% nitric acid solution and 5% sodium hydroxide solution.



For power units with VVER reactors, an additional solution containing 1.600% boric acid, 0.300% KOH, and 0.025% hydrazine hydrate.



Decontamination factor (ability to be washed free of radioactive contamination) must be confirmed by a numerical value.



Surface condition after exposure: smooth, monolithic, with no blistering, peeling, or loss of adhesion.



4. Conclusion of the Lead Materials Science Organization (LMSO)

Purpose: scientific and technical expert review confirming that the properties of the new material are equivalent to or better than those of previously approved analogues.



Regulatory basis: the obligation to involve the LMSO is established in nuclear-industry regulatory documents, including PNAE G-7 and industry standards. Without the LMSO conclusion, the technical documentation is not accepted for review by Rostechnadzor.



Report requirements (according to Appendix No. 4 to NP-010-16, Rules for Localizing Safety Systems of Nuclear Power Plants):

The report must include:



• chemical composition of the material;



• heat-treatment modes (if applicable);



• strength, elasticity, and thermal-conductivity values;



• characteristics in the temperature range from 20°C to Tmax, as well as at values exceeding Tmax by 25°C, 50°C, and 100°C.



5. Certificate of Conformity (Legal Approval by Rostechnadzor)

Purpose: the final legal document certifying that the product complies with federal rules and regulations in the field of nuclear energy use.



Issuance procedure: the certificate is issued based on analysis of the entire collected package (product passport, qualification test reports, LMSO conclusion). The list of products subject to mandatory certification in this system was approved by Rostechnadzor Order No. 277 dated July 21, 2017.



Legal significance: the existence of the certificate gives construction control grounds to admit the material for installation at the facility.



6. Decontamination Report (Confirmation under GOST R 51102-97)

Purpose: documentary evidence that the coating can be cleaned of radioactive contamination using standard means without destroying its own structure.



Mandatory nature: the report is required for all coatings introduced into the strict-regime zone (SRZ) of an NPP.



Test method: the coating is applied to a sample, contaminated with radioactive indicators, and then washed using the decontamination-solution formulations specified in GOST 26825-86 and GOST R 51102-97. The decontamination factor is measured and compared with the standard. The supervisory authority verifies that the formulation complies with these standards specifically, not with arbitrary manufacturer specifications.



7. Inclusion in the Consolidated List (Industry List of Principal Materials)

Purpose: final recognition of the material in the industry regulatory framework, allowing general contractors to order it under the standard procedure without repeated approval.



Procedure: after successful completion of all previous stages, the material is included in the Consolidated List of standardization documents in the field of nuclear energy use or in the industry list of principal materials. Inclusion is formalized by a special protocol of the lead industry materials-science body.



Consequences: after inclusion in the list, the material is considered legitimized, and its use at subsequent facilities does not require repeating the full procedure; reference to the list is sufficient.



Conclusions and Recommendations

The use of a new protective coating at facilities using nuclear energy is possible only if a complete documented trail exists, including the seven elements listed above. The recommended strategy is to prepare the document package at the pre-supply stage, before installation work begins. A properly prepared factory passport, PNAE G-7 qualification test reports, LMSO conclusion, and certificate of conformity make it possible to pass Rostechnadzor construction control without delays.



TechAtomStroy assists in preparing documentation packages for the legitimization of paint-and-varnish and protective coatings for the requirements of a specific facility. To obtain consultation and support for qualification testing, send the material specification through the feedback form on the website.



*This material was prepared on the basis of an analysis of the following regulatory documents: NP-041-22, NP-010-16, PNAE G-7-010-89, GOST R 51102-97, GOST 26825-86, and Rostechnadzor Order No. 277.*

Abstract. This article presents experience in using high-build polymer compounds for anti-corrosion protection of NPP steel structures. It examines technological solutions that reduced the duration of work by 20% while maintaining compliance with NP-041-22 requirements. The material is intended for specialists involved in construction and reconstruction at facilities using nuclear energy.



Relevance of the Problem

Corrosion damage to steel structures at facilities using nuclear energy (FUNE) is a significant factor that reduces reliability and safety. Maintaining the integrity of load-bearing and enclosing structures requires the timely and high-quality application of protective coatings. The traditional technology, which involves sequential application of a primer and several finish coats with process pauses for polymerization, creates bottlenecks and risks disrupting adjacent works under tight construction schedules.



During work at one safety class 2 facility, the general contractor faced a time constraint in which the classic 'primer + 2-3 enamel coats' scheme did not provide the required productivity. A technical solution was needed to reduce the duration of anti-corrosion treatment of NPP steel structures without lowering the protection class or coating durability.



Selection of a Technological Alternative

Specialists of TechAtomStroy proposed and implemented the replacement of traditional paint-and-varnish materials with high-build polymer compounds and high-solids epoxy enamels. The key technical differences of the approach used were as follows:

The high viscosity and adhesion of the material make it possible to form a monolithic coating in a single cycle, eliminating the need for a multilayer structure. An additional advantage is improved maintainability and resistance to radiation exposure, which is critical for controlled access zones and rooms containing safety-system equipment.



Organization of the Production Process

The entire technological process was adapted to the requirements applicable to work at nuclear power facilities and included the following stages.



1. Surface Preparation

Abrasive blasting was carried out to Sa 2.5 according to ISO 8501-1 (complete removal of contaminants and a visually clean metal surface). The roughness profile was measured. For safety class 2 steel structures, this level of cleaning is mandatory in accordance with NP-041-22 requirements.



2. Priming

A high-build zinc-rich primer was used, providing both barrier and electrochemical protection. The material was applied by airless spraying.



3. Application of the Finish Coating

The finish layer was formed in one pass to a thickness of 600 microns. Thickness control was performed by visual and magnetometric methods on every square meter of the surface.



4. Quality Control

Adhesion tests (cross-cut method) and porosity checks using a spark holiday detector were performed. The results were recorded in non-destructive testing reports, which are mandatory documents for acceptance of the work by Rostechnadzor.



Achieved Results

The use of high-build polymer compounds at the safety class 2 facility produced the following quantitative results:



• The total duration of anti-corrosion treatment was reduced by 20% by decreasing the number of layers and eliminating intercoat downtime.

• Labor requirements for painting personnel and auxiliary operations were reduced (covering adjacent zones, installation and dismantling of scaffolding).

• The handover of the work front to adjacent divisions was accelerated, which helped maintain the general contractor's schedule.



Conclusions and Recommendations

Based on the implemented project, TechAtomStroy recommends that general contractors and subcontractors performing anti-corrosion treatment of NPP steel structures consider high-build polymer compounds as an effective tool for optimizing construction production. This technology not only reduces calendar time but also provides the required level of coating reliability and durability when NP-041-22 regulatory requirements are observed.



To obtain a detailed assessment of the applicability of this technology at your facility, including analysis of the specification and calculation of projected savings in time and labor, send a request to the technical department of TechAtomStroy through the feedback form on the website.



*This material is advisory in nature and is based on practical experience in performing work at safety class 2 facilities.

This article examines the specific features of roofing works on buildings and structures of nuclear power plants. It provides a comparative analysis of the two main types of roof coverings: membrane (polymer) roofing and torch-applied (bitumen-polymer) roofing. It analyzes the regulatory requirements of NP-041-22, SP 17.13330.2017, fire-safety rules, and criteria for selecting a roofing system for different responsibility classes. The technological stages of roofing installation, quality-control requirements, and service lives are presented.



The roof is one of the most critical building elements, protecting building structures and interior spaces from atmospheric exposure. At facilities using nuclear energy (FUNE), roofing works are subject to increased requirements: reliability, durability (at least 30-50 years), maintainability, and, for strict-regime zones, decontaminability.



Nuclear power plants and related enterprises operate buildings of different safety classes, from the main reactor-building structure (class 1-2) to auxiliary administrative and amenity buildings (class 4). Depending on the safety class, structural features, and operating conditions, the roofing system is selected: membrane (polymer) or torch-applied (rolled bitumen-polymer). Each technology has its own advantages, limitations, and production requirements.



Regulatory Framework for Roofing Works at NPPs

Roofing works at facilities using nuclear energy are governed by the following documents:



• NP-041-22, Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Structures, establishes safety classes for building structures, including roof coverings, and requirements for their durability and resistance to impacts.

• SP 17.13330.2017, Roofs (updated version of SNiP II-26-76), is the main document regulating the design and installation of all types of roofs.

• SP 118.13330.2022, Public Buildings and Structures, applies to roof requirements for administrative buildings.

• Fire Safety Rules in the Russian Federation (Resolution No. 1479) set requirements for the use of open flame when torch-applying rolled materials, which is especially relevant at controlled-access facilities.

• GOST R 51102-97 (for roofs in strict-regime zones) establishes decontaminability requirements for coatings if the roof may be subject to radioactive contamination.



NPP sites also have internal industry regulations that prohibit or restrict the use of open flame on operating power units. In such cases, preference is given to membrane roofing with mechanical or ballast fastening.



Comparative Analysis of Roofing Systems

Membrane (Polymer) Roofing

Membrane roofs are made of polyvinyl chloride (PVC), thermoplastic polyolefins (TPO), or ethylene-propylene-diene monomer rubber (EPDM). Installation is performed without open flame: sheets are welded with hot air (PVC, TPO) or bonded (EPDM).



Advantages of membrane roofing:



• High elasticity and resistance to temperature deformation and vibration.

• Durability: service life of 30-50 years (up to 50 years is claimed for TPO).

• Installation without open flame: possible to perform work on operating power units.

• High maintainability: local repair by welding.

• Low weight (1.2-2.0 kg/m²), with no need to strengthen structures.

• Resistance to aggressive media (boric acid, decontamination solutions).



Limitations:



• Higher cost (materials and labor) compared with two-layer bitumen systems.

• Requirement for a flat and strong substrate.

• PVC membranes are sensitive to bitumen, so compatibility with the substrate must be checked.



Torch-Applied (Bitumen-Polymer) Roofing

Torch-applied roofing is a multilayer system of rolled materials based on bitumen modified with polymers (styrene-butadiene-styrene, atactic polypropylene). Installation is carried out using gas burners (open flame).



Advantages of torch-applied roofing:



• Lower cost compared with membrane roofing.

• A technology proven over decades, with a wide selection of materials.

• High mechanical strength in two- or three-layer systems.

• Resistance to point loads and personnel traffic.



Limitations:



• Use of open flame: at operating NPPs this is often restricted or requires a work permit and fire-prevention measures.

• Shorter service life: 15-25 years for high-quality bitumen-polymer systems, compared with 30-50 years for membranes.

• Higher weight (5-10 kg/m²), requiring verification of the load-bearing capacity of floors.

• More complex repair (local torch application while maintaining overlaps).

Selection of the Roofing System for NPP Buildings

When selecting a roof type for buildings and structures of a nuclear power plant, the following factors are considered:



1. Safety class of the building under NP-041-22: for class 1-2 buildings that affect safety, membrane roofing with a service life of at least 40 years confirmed by testing is recommended.

2. Operating mode: flame-free technologies (membrane roofing) are preferred on operating power units.

3. Floor/slab structure: where load-bearing capacity is limited (wooden or light-metal coverings), membrane roofing is safer.

4. Budget and planned service life: for temporary or auxiliary buildings (class 4, service life 15-20 years), torch-applied roofing may be economically justified.



5. Fire-safety requirements: for category A, B, and C rooms (explosion and fire hazardous) and zones where hydrogen systems are located nearby, the use of open flame is prohibited, making membrane roofing the only acceptable option.



Roofing Installation Technology

Membrane Roofing (Using Mechanical Fastening as an Example)

1. Substrate preparation: cleaning, leveling, and priming if necessary. Permissible deviations are not more than 10 mm over 2 meters.

2. Installation of vapor barrier (polyethylene film or bitumen-polymer vapor barrier) with taped seams.

3. Installation of thermal insulation (high-density mineral-wool boards) in two layers with staggered joints. Fastening with telescopic fasteners (2-4 pieces per board).

4. Installation of a separation layer (glass mat, geotextile) to protect the membrane from contact with bitumen if a bitumen vapor barrier is used.

5. Rolling out and welding the membrane: sheets are welded with hot air with a 50-80 mm overlap. Weld quality is checked visually and with a spatula/probe.

6. Mechanical fastening of the membrane to the insulation and substrate using telescopic fasteners with enlarged washers at junctions and along the perimeter.

7. Arrangement of junctions to parapets, drains, and pipes: special profile elements, PVC collars, and sealing.

8. Drainage funnels: the membrane is led into the funnel bowl and sealed.

9. Roof testing (water flooding or spray testing) with preparation of a certificate.



Torch-Applied Bitumen-Polymer Roofing

1. Substrate preparation: cleaning, dust removal, and priming with bitumen primer. Primer drying time is 1-2 hours.

2. Installation of vapor barrier (torch-applied bitumen vapor barrier).

3. Installation of thermal insulation (high-density mineral-wool boards) by mechanical fastening or bonding with bitumen mastic.

4. Torch application of the lower layer of rolled material: the underside of the roll and the substrate are heated with a burner; the roll is unrolled and pressed with a roller. The overlap must be at least 80 mm.

5. Torch application of the upper layer with seams offset by 300 mm relative to the lower layer.

6. Arrangement of junctions: application of additional layers extending 250-300 mm onto vertical surfaces, with seams bonded using bitumen mastic.

7. Installation of funnels and water-collection gutters.

8. Fire-prevention measures during work at NPPs: fire extinguishers, fire blankets, work permit, and supervision.



Quality Control of Roofing Works

• Incoming inspection of materials (certificates, passports, marking, and compliance with the design).



• Operational control: continuity and tightness of welded seams (probe, visual inspection, and for membranes also peel or air-pressure testing), thickness of torch-applied layers, and flatness of the substrate.



• Acceptance control: hydraulic or rain test certificate (water flooding for 2 hours, no leaks). For membrane roofs, additional measurement of coating thickness and checking of adhesion to the substrate are performed.



• For nuclear-industry facilities, control is carried out with construction-control participation and documented in concealed-work certificates (certificates for vapor barrier, thermal insulation, and each roof layer).



Conclusions and Recommendations

When selecting and installing roofing on buildings and structures of nuclear power plants, it is recommended to:



1. For safety class 1-2 buildings and operating power units, use membrane roofing (PVC, TPO) with a service life of 40-50 years, since it is installed without open flame and is more maintainable.



2. For auxiliary buildings (class 4) and new construction on non-operating industrial sites, torch-applied bitumen-polymer roofing with a service life of 15-25 years may be used when the budget is limited.



3. Ensure substrate preparation with control of screed moisture (not more than 4% for bitumen materials and not more than 8% for membranes).



4. Comply with thermal-insulation requirements: for roofs over dry rooms, one layer is sufficient; over humid/heated rooms, vapor barrier and a ventilated air gap may be required.



5. Perform roof tests and prepare as-built documentation in accordance with Rostechnadzor requirements.



To obtain a commercial proposal for roofing works (installation of membrane or torch-applied roofing) at your facility, including substrate preparation, thermal insulation, vapor barrier, drainage systems, quality control, and documentation handover, send a technical specification indicating the building type, its safety class under NP-041-22, roof area, and service-life requirements to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, work schedule, and recommendations for selecting the optimal roofing system will be prepared.



*This material was prepared on the basis of NP-041-22, SP 17.13330.2017, fire-safety rules, and GOST R 51102-97.*

Abstract. This article examines additional parameters for selecting fire-protective coatings for steel structures at facilities using nuclear energy (FUNE). It shows that focusing exclusively on the fire-resistance rating (R) is insufficient. The article analyzes material behavior during a beyond-design-basis accident, toxicity of thermal-decomposition products, decontaminability, and radiation resistance. Recommendations for selecting compositions are provided on the basis of practical experience.



Introduction: Limitations of an Approach Based Only on the R Factor

When designing fire protection for load-bearing steel structures of NPP buildings and facilities, the standard requirement is to provide a specified fire-resistance rating (R90, R120, and above). However, nuclear energy is governed by a set of industry regulatory documents - NP-509, NP-511, and federal rules and regulations in the field of nuclear energy use - which impose additional and often stricter requirements on fire-protective materials.



The classic R parameter, meaning the ability of a structure to retain its load-bearing capacity under the standard temperature regime, is necessary but not sufficient. Without considering such characteristics as radiation resistance, smoke toxicity, decontaminability, and stability of properties throughout the entire assigned service life, a material cannot be approved for use at NPP facilities.



Comparative Analysis of Types of Fire-Protective Compounds

Two main categories of fire-protective materials for steel structures are available on the market. Their key characteristics are shown in the table.

Thus, the choice between the two main types is a compromise among coating weight, radiation resistance, and the complexity of decontamination.



Critical Parameters for NPP Facilities

Toxicity of Combustion Products and Gas Emissions

In sealed rooms of nuclear power plants, such as reactor halls, cells, and control corridors, even short-term release of toxic substances during a fire can lead to unacceptable consequences for personnel. Many organic intumescent compounds contain halogen-bearing components that form hydrogen chloride, hydrogen fluoride, and other highly toxic gases during thermal degradation. The use of such materials at NPP facilities is prohibited by industry standards.



Coating Decontaminability

For strict-regime zones and rooms where radioactive contamination is possible, the fire-protective coating must be easily cleaned of radioactive particles with standard decontamination solutions. Porous or chemically unstable coatings retain contamination, making further operation impossible. Even with satisfactory fire resistance, a material that has not passed decontaminability testing under GOST R 51102-97 is not admitted for use.



Behavior During a Beyond-Design-Basis Accident

In accidents involving possible hydrogen release, for example during depressurization of the primary circuit, the absence of spark generation and the coating's ability not to contribute to hydrogen explosion become critical. Some coatings may release catalysts or generate sparks when heated; such materials are excluded from consideration.



Hybrid Solutions: Liquid-Glass-Based Coatings

A compromise option that combines the high fire resistance of inorganic systems with acceptable weight is hybrid coatings based on potassium or sodium liquid glass. Their key features are as follows:



• When heated to temperatures above 100-120°C, the material releases chemically bound water, which evaporates, removes heat from the steel structure, and creates a steam barrier.

• The process has a 'pendulum' character: as the material cools, it sorbs moisture from the air again and restores its properties.

• There are no halogens or other toxic components.

• The coating has a smooth, low-porosity surface, which ensures high decontaminability.

• Radiation resistance is sufficient for the entire assigned service life.



This type of material is recommended for use in enclosed volumes with a potential risk of hydrogen explosions, as well as in controlled access zones.



Example of Selecting Fire Protection for a Package Transformer Substation

As an illustration, consider the selection of a fire-protective compound for a package transformer substation - a facility with a high risk of oil fires and rapid temperature rise in the event of an accident.



Initial design requirements:



• Fire-resistance rating of steel structures: R120.



• Prohibition on the use of halogen-containing materials.



• Location of the facility in a zone where decontamination after an accident may be required.



Adopted solution:

A two-layer system was selected:



Epoxy-based adhesion primer to ensure reliable bonding with the metal.



Finish coating: a hybrid liquid-glass compound with pendulum moisture release.



Results:



A full cycle of fire tests was performed on witness specimens.

Effectiveness was confirmed at exposure temperatures up to 1100°C.

The absence of halogens and other toxic elements in the formula was documented.

A test report accepted by Rostechnadzor construction control was obtained.

The facility was commissioned with no comments regarding fire protection.



Conclusions and Recommendations

When selecting fire protection for NPP steel structures, it is unacceptable to focus only on the fire-resistance limit under the standard temperature regime. The mandatory assessment must include:



• radiation resistance of the material throughout its service life;

• toxicity of thermal-decomposition products, including the absence of halogens;

• decontaminability in accordance with GOST R 51102-97;

• behavior during a beyond-design-basis accident, including hydrogen release and spark generation;

• stability of properties after repeated wetting and drying for hybrid compounds.



Based on completed projects, TechAtomStroy recommends considering hybrid liquid-glass coatings as the preferred solution for most NPP zones, except where coating weight is critically limited and intumescent systems with confirmed radiation resistance are acceptable.



To obtain consultation on selecting a fire-protective compound for the specific features of your facility, including required fire-resistance rating, room category, and radiation load, send the technical specification to the TechAtomStroy department through the feedback form on the website.



*This material is based on practical experience in implementing fire-protection projects for NPP facilities and on analysis of regulatory documentation (NP-509, NP-511, NP-041-22).*

This article examines the principles of designing technical gas supply systems at facilities using nuclear energy. It analyzes regulatory requirements for compressed air systems used to supply instrumentation and control equipment, automation systems, and personnel breathing air. It also presents safety-class classification, air quality requirements, redundancy requirements, and recommendations for equipment selection and installation quality control.



Introduction

Technical gas supply systems at nuclear power plants supply compressed air to pneumatic valve actuators, instrumentation, and process automation control systems. In addition, compressed air is used to create overpressure in rooms, protect equipment from radioactive aerosols, and provide breathing air for personnel in protective structures.



Unlike general industrial systems, technical gas supply at facilities using nuclear energy (OIAE) is governed by increased requirements for reliability, redundancy, and compressed air quality. Air supply to control systems and emergency protection systems must be guaranteed even under beyond-design-basis accident conditions.



Regulatory Framework

The design and operation of compressed air systems at nuclear power plants are regulated by the following documents:



• NP-001-15 “General Provisions for Ensuring the Safety of Nuclear Power Plants” establishes the classification of systems by safety class. Technical gas supply systems that supply safety-related equipment are assigned to Safety Class 2 or 3.



• Rules for the Design of Gas Supply Systems (SP 62.13330.2011) apply to the installation of external gas pipelines for gaseous media.



• ASME AG-1 “Code on Nuclear Air and Gas Treatment” establishes requirements for air and gas treatment equipment used in nuclear safety systems.



According to NP-001-15, compressed air supply networks must have buffer vessels (receivers) that provide air supply to control and monitoring systems for a period sufficient for the safe shutdown of the facility, but not less than one hour.



Classification of Technical Gas Supply Systems

By functional purpose, the systems are divided into three categories.



1. Compressed air systems for instrumentation and control (I&C) and automation supply pneumatic valve actuators, regulators, and positioners. They require a high degree of purification from oil, moisture, and mechanical particles (not lower than Contamination Class 1) and guaranteed supply in the event of a power outage.



2. Compressed air systems for overpressure and sealing create excess pressure in rooms with potential radioactive contamination. They require continuous supply and automatic switchover to the standby system.



3. Compressed air systems for personnel breathing provide air for operating personnel in protective structures and supply hose respirators and pneumatic suits. Air quality must comply with hygienic standards for oxygen, carbon dioxide, oil, and moisture content.



Compressed Air Quality Requirements

The quality of compressed air for I&C systems and emergency protection systems must be not lower than Contamination Class 1 under state standards. The main Class 1 parameters are:



• solid particle content of no more than 0.1 mg/m³, with a maximum inclusion size of no more than 1 µm;



• water content by pressure dew point not higher than -40°C;



• oil content in liquid and aerosol form of no more than 0.01 mg/m³.



For personnel breathing systems, oxygen content (19-23% by volume), carbon dioxide content (not more than 0.5% by volume), toxic impurities, and the absence of odor are additionally monitored.



System Composition and Arrangement

A typical technical gas supply system includes the following main elements.



The air intake unit is equipped with coarse filters to protect the compressor from atmospheric dust. The intake point must be located in an area with minimal dust levels and no ingress of exhaust gases.



The compressor unit is the main source of compressed air. Nuclear power plants use oil-injected or oil-free screw compressors. For I&C supply, oil-free compressors or oil-injected compressors with a highly efficient oil separation system are preferred.



The air receiver is a buffer vessel that smooths pulsations and ensures consumer supply when compressors stop. Its volume is calculated based on maximum flow rate and the required autonomous operating time (not less than one hour).



Compressed air dryers may be refrigerated dryers (dew point +2 to +5°C for general industrial networks) or adsorption dryers (dew point down to -40 to -70°C for critical I&C and breathing systems).



The filtration system provides staged purification: oil separators after the compressor, microfilters (0.1-1 µm), and activated carbon adsorbers before supply to I&C and breathing systems.



Pipelines made of seamless steel pipes (for pressures up to 1.6 MPa) are laid with a slope toward drainage points and equipped with condensate drains at low points.



The monitoring and automation system continuously monitors pressure, dew point, and oil content in the compressed air.



Redundancy and Reliability

Technical gas supply systems at nuclear power plants are designed with 100% redundancy. The standard solution is two independent compressor units operating in hot standby mode. When pressure in the receiver drops below the setpoint, the standby compressor starts automatically.



Each compressor must have its own power supply input from different sections of the distribution switchgear. For pneumatic actuators whose failure is critical to safety, local accumulators sized for one full stroke of the valve stem are additionally provided.



According to regulatory requirements, buffer vessels must provide air supply to control and monitoring systems when compressors are stopped for a period sufficient for the safe shutdown of the facility, but not less than one hour.



Installation and Quality Control

Installation of technical gas supply systems at OIAE facilities is carried out according to a work execution plan developed in accordance with industry standards (STO 95 104-2015). Quality control includes:



• incoming inspection of pipes and fittings (certificates, visual inspection);



• radiographic or ultrasonic inspection of welded joints (scope of at least 10% for Safety Class 3 systems and 50-100% for Safety Class 2 systems);



• pneumatic strength and leak-tightness testing (pressure of 1.25 x operating pressure, 24-hour hold, pressure drop of no more than 1%);



• inspection of internal cavity cleanliness (purging with filters at consumer inlets);



• in strict regime zones, inspection of weld smoothness to prevent the accumulation of radioactive contamination.



Operational Maintenance

During operation, the following activities are performed regularly: monitoring the dew point at dryer outlets; replacing filter elements according to schedule or when the pressure drop limit is exceeded; draining condensate from receivers and low points of air ducts; and periodic analysis of compressed air quality at control points (at least once per quarter for Safety Class 2 systems).



Conclusions

Technical gas supply at facilities using nuclear energy is a critical engineering system on whose reliability the safety and operability of the reactor installation depend. Compressed air for I&C, automation, and personnel breathing must meet specified cleanliness parameters (Contamination Class 1), be dried to a dew point below -40°C, and remain guaranteedly available in the event of compressor failure through air receivers designed to operate for at least one hour. Compliance with the requirements of NP-001-15, design rules, and ASME AG-1 standards makes it possible to create a compressed air system capable of operating without failures throughout the entire service life of the power unit.



To receive a commercial proposal for the design, supply, and installation of technical gas supply systems for your facility, please send the technical assignment to the commercial department of TechAtomStroy LLC via the feedback form on the website.



*Prepared based on NP-001-15, SP 62.13330.2011, and ASME AG-1.*

This article examines the requirements for water-treatment systems intended to produce deionized (demineralized) water used in cleanrooms in nuclear energy, pharmaceuticals, and microelectronics. It analyzes technological schemes such as reverse osmosis, ion exchange, and electrodeionization; the classification of water quality under ISO 3696, ASTM D1193, and pharmacopoeias (USP, EP, State Pharmacopoeia); and purity indicators including resistivity, total organic carbon (TOC), bacteriological purity, and endotoxin levels. Recommendations are provided for designing water-treatment systems for cleanrooms, including requirements for pipeline materials, quality control, and validation.



Introduction. Ultrapure Water as a Process Medium

For facilities using nuclear energy, pharmaceutical enterprises, and microelectronics production, ultrapure water is a critical technological resource. At NPPs, deeply demineralized (deionized) water is used for make-up of steam boilers, turbines, and heat-recovery boilers operating at pressures of up to 140 atm. In controlled access zones, the chemical composition of the primary- and secondary-circuit coolant must prevent corrosion of structural materials and accumulation of activated impurities.



In the pharmaceutical industry, water-quality requirements are even stricter. Purified Water and Water for Injection must not contain pyrogens, endotoxins, or microbial contamination. The latest GMP requirements state that pharmaceutical water must be at least of drinking-water quality, while the design, installation, operation, and maintenance of water-purification equipment must ensure compliance with established quality standards.



The microelectronics industry also imposes extremely stringent requirements: Type I water, with resistivity of 18.2 MOhm·cm, is used for final wafer rinsing and chip production, where even nanograms of impurities can cause rejects.



This article summarizes regulatory requirements for deionized-water quality, technological methods for obtaining it, and practical recommendations for designing water-treatment systems for cleanrooms.



Regulatory Framework for Deionized-Water Quality

Deionized (demineralized) water is classified under international and national standards. There are no uniform requirements for physical and chemical parameters; the required purity class is determined by industry regulations and the technological process.



1. Laboratory Standards: ISO 3696, ASTM D1193

ISO 3696:1999 (in Russia, GOST R 52501-2005) establishes three types of pure water for laboratory analysis:



• Type I (ultrapure water): resistivity >=18.2 MOhm·cm at 25°C, TOC < 50 ppb, no particles or bacteria. It is used in sensitive analysis, for preparation of standard solutions, and in microelectronics.

• Type II (deionized water): resistivity >=5 MOhm·cm at 25°C, TOC < 30 ppb. It corresponds to the requirements of general chemical or biological experiments.

• Type III (water produced by reverse osmosis): resistivity >=0.5 MOhm·cm. It is used for laboratory glassware, feeding distillers, and autoclaves.



ASTM D1193-06 (Reagent Water) establishes similar quality classes for laboratory-grade pure water.



2. Pharmacopoeial Standards: USP, EP, State Pharmacopoeia

Water-treatment systems in pharmaceuticals must comply with GMP. The United States Pharmacopeia (USP) distinguishes Purified Water, Water for Injection, and Highly Purified Water. Key indicators for Purified Water include conductivity <1.3 µS/cm at 25°C, TOC <500 ppb, and absence of bacterial growth.



In Russia, the State Pharmacopoeia (OFS.2.2.0020.15 'Purified Water') applies, as does the European Pharmacopoeia (EP), which regulates similar parameters. Reverse osmosis, electrodeionization, and distillation are specified as the main technological methods permitted for producing pharmaceutical-grade water.



3. Application at NPPs: Special Technical Conditions

The technology for producing deeply demineralized water at nuclear power plants is governed by RD 24.031.120-91, GOST 20995-75, SO 153-34.20.501-2003, and technical operation rules. Coolant-quality requirements directly depend on reactor type (VVER, RBMK, BN) and circuit pressure. Traditionally, distillation was used to produce water with specific electrical resistance of 0.2 MOhm·cm (specific conductivity of 5 µS/cm) from water with salinity up to 1000 mg/L, but since the 1990s ion exchange, reverse osmosis, and electrodialysis methods have become increasingly widespread.



Technologies for Producing Deionized Water

A typical water-treatment system includes sequential purification stages: preliminary mechanical filtration, softening, reverse osmosis, deionization (ion exchange), and final polishing (electrodeionization, UV sterilization, ultrafiltration).



1. Mechanical Filtration and Softening - Pretreatment

Removal of suspended particles, sand, rust, and chlorine is carried out on sand-carbon and cartridge filters. Water softening (Na-cation ion exchange) is necessary to reduce hardness before reverse osmosis and to protect membranes from calcium-carbonate deposits.



2. Reverse Osmosis - Barrier Purification

Water under pressure is passed through a semipermeable membrane that retains up to 99% of dissolved salts, bacteria, viruses, and organic molecules. Reverse osmosis substantially reduces the load on ion-exchange resins and increases their service life.



3. Ion Exchange - Deep Deionization

Water deionization (demineralization) is the key process that removes ions of inorganic salts. It is performed by passing water through columns filled with two types of ion-exchange resins:



• Cation exchanger R-H: binds metal cations (sodium, calcium, magnesium, iron), releasing H+ ions in exchange.



• Anion exchanger R-OH: binds anions of acid residues (chlorides, sulfates, nitrates, silicates), releasing OH- ions in exchange.



The resulting H+ and OH- ions combine into neutral H2O molecules. The ion-exchange process is reversible: exhausted resins are regenerated by passing acid solutions through the cation exchanger and alkali solutions through the anion exchanger.



To obtain deeply demineralized water with resistivity up to 18 MOhm·cm, two-stage H-OH ionization schemes are used. Mixed-bed resin filters (MBF - cation and anion exchangers in one column) are also used for final polishing to ultra-high resistivity.



4. Electrodeionization (EDI) - Reagent-Free Deep Demineralization

Electrodeionization is a technology combining ion exchange and electrodialysis. Under the influence of an electric field, ions are drawn out of the water stream through ion-exchange membranes, while the resin inside the chambers is continuously regenerated by water dissociation into H+ and OH- ions. EDI units produce water with resistivity >18 MOhm·cm without the use of chemical reagents.



For EDI systems, it is critically important to ensure high inlet-water quality, usually after reverse osmosis, so that membranes and resins are not contaminated.



5. Final Polishing for Ultrapure Water (Type I)

• UV lamp with wavelengths of 185 nm and 254 nm: reduces TOC by oxidizing organics to CO2 and provides sterilization by destroying bacteria.



• Ultrafiltration (UF): a capillary membrane removes pyrogens, endotoxins (lipopolysaccharides from gram-negative bacterial membranes), and nucleic-acid fragments.



• Membrane or vacuum degassing: removal of dissolved oxygen, nitrogen, and CO2.



For ultrapure water (18.2 MOhm·cm at 25°C, TOC <3 ppb, endotoxins <0.001 EU/mL, bacteria <0.01 CFU/mL), all listed modules are mandatory.



Design of Water-Treatment Systems for Cleanrooms

When implementing water-treatment systems at nuclear and pharmaceutical facilities, the following principles must be considered:



• Pipeline materials: high-purity polymers (PVC-C, PP, PVDF) or electropolished 316L stainless steel. In pharmaceuticals, welded joints are made by automatic orbital welding with surface-cleanliness control (Ra <0.6 µm).



• Minimization of stagnant zones: there must be no dead legs in pipelines (design according to ASME BPE requirements); the recirculation pump must provide turbulent flow (velocity >1.5 m/s) to prevent biofilm formation.



• Quality control (online monitoring): resistivity/conductivity meters, TOC sensors, and bacteriological analyzers (ATP metering).



• Validation (in pharmaceuticals): qualification of water-treatment and distribution systems (IQ/OQ/PQ). Periodic sampling of water in the loop is performed to control chemical and microbiological purity.



Conclusions

A reliable water-treatment system for producing deionized water is an integral part of the engineering infrastructure of NPPs, pharmaceutical plants, and microelectronics production facilities. The choice of technological scheme (ion exchange, reverse osmosis, EDI) and water-purity class (Type I/II/III under ISO 3696, Purified Water/Water for Injection under pharmacopoeias) is determined by the regulatory requirements of the specific technological process.



TechAtomStroy performs turnkey design, supply, installation, and commissioning of water-treatment systems for cleanrooms of any category, including closed-loop deionized-water systems with quality control (conductivity, TOC, bacteria). All work is performed in compliance with GMP requirements where necessary, nuclear-industry standards, and Rostechnadzor requirements.



To obtain a commercial proposal for designing and building a water-treatment system for your facility, send a technical specification indicating the required water-purity class, capacity, and industry-specific conditions to the commercial department of TechAtomStroy LLC through the feedback form on the website. A cost estimate, work schedule, and feasibility study for selecting the optimal technological scheme will be prepared.



This material was prepared on the basis of ISO 3696:1999, ASTM D1193-06, the State Pharmacopoeia of the Russian Federation (OFS.2.2.0020.15), USP, EP, and nuclear-industry regulatory documents (RD 24.031.120-91, PTE).

This article examines the specific features of waterproofing and thermal-insulation works for structures and buildings at facilities using nuclear energy (FUNE). It analyzes the requirements of NP-041-22 and NP-010-16 for insulation systems for different safety classes. The article presents the types of materials used (bitumen, polymer, mineral-wool, and polymer-foam materials), their application technologies, and quality-control methods. It shows the role of waterproofing and thermal insulation in ensuring the service life of NPP buildings and reducing operating costs.



Waterproofing and thermal insulation of building structures are critical elements for ensuring the durability and safe operation of nuclear power plant buildings and structures. Damage to insulation layers leads to wetting of load-bearing structures, corrosion of reinforcement, reduced thermal performance, and, in radiation-controlled zones, accumulation of contamination and deterioration of surface decontaminability.



For facilities using nuclear energy, requirements for waterproofing and thermal insulation are stricter than in general industrial construction. This is due to the need to ensure nuclear and radiation safety, long operating periods (60 years or more), and special conditions: exposure to ionizing radiation, aggressive media (boric acid, decontamination solutions), elevated temperatures, and vibration.



Regulatory Framework for Waterproofing and Thermal Insulation at NPPs

The basic documents in the field of building structures are:



• NP-041-22, Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Structures, establishes safety classes for structures and requirements for their protection from external and internal factors, including moisture and temperature effects.

• NP-010-16, Rules for Localizing Safety Systems of Nuclear Power Plants, regulates requirements for the leak tightness of enclosing structures and systems that prevent the spread of radioactive substances. In this context, waterproofing is one of the safety barriers.

• SP 50.13330.2012, Thermal Protection of Buildings (updated version of SNiP 23-02-2003), applies to requirements for the reduced thermal resistance of enclosing structures.

• SP 71.13330.2017, Insulation and Finishing Coatings, contains general requirements for waterproofing and thermal-insulation works.

• GOST 31309-2009, Thermal Insulation Building Materials and Products. General Technical Specifications, regulates the main parameters of thermal-insulation materials.

• For strict-regime zones, GOST R 51102-97 (decontaminability of coatings) and GOST 26825-86 (resistance to decontamination solutions) are additionally applied, including to insulation systems if they are exposed in an accessible zone.



Classification of Waterproofing Materials for Facilities Using Nuclear Energy

Depending on purpose and operating conditions, the following main types of waterproofing are used:

A key requirement for waterproofing NPP structures is high adhesion to concrete and metal, chemical resistance to boric acid and decontamination solutions, and radiation resistance for strict-regime zones. Polyurea coatings are the preferred solution for critical zones (spent-fuel pools, deaerator racks) due to their elasticity, monolithic structure, and service life of up to 50 years.



Classification of Thermal-Insulation Materials

For thermal protection of NPP buildings and structures, materials are used that provide the specified thermal resistance with minimum thickness and weight while taking radiation resistance and non-combustibility into account.

For thermal insulation at facilities using nuclear energy, non-combustibility (NG or G1 class) and the ability to retain thermal properties when exposed to decontamination solutions and elevated temperatures (up to 150-200°C for pipelines) are mandatory requirements. Basalt-based mineral-wool materials meet these requirements and are the main type of thermal insulation used at NPPs.



Technology for Waterproofing and Thermal-Insulation Works

Substrate Preparation

1. Cleaning the surface from dirt, dust, oils, and remains of cement laitance (milling or sandblasting).

2. Surface leveling: permissible irregularities not more than 5 mm over 2 meters for rolled waterproofing and not more than 3 mm for coating waterproofing.

3. Drying the substrate to a moisture content not exceeding 4% by weight for bitumen materials and 8% for polymer materials.

4. Priming to improve adhesion and remove dust.

5. For concrete structures with penetrating waterproofing: ensuring an open pore structure and saturating with water before application.



Waterproofing Installation

Torch-applied rolled waterproofing:



• Application of bitumen primer, drying for 1-2 hours.

• Torch application of the lower layer with sheet overlaps of 100-150 mm.

• Torch application of the upper layer with seams offset.

• Control of continuity and adhesion.



Coating polymer-cement waterproofing:



• Preparation of the mortar according to the instructions.

• Application by brush or roller in 2-3 layers with intermediate drying.

• Total layer thickness from 2 to 6 mm.



Penetrating waterproofing:



• Wetting the concrete to a saturated condition.

• Application of the compound (brush, sprayer) in 2 layers.

• Maintaining a moist condition for 3-7 days.

• Testing under hydrostatic pressure.



Sprayed polyurea:



• Surface preparation (abrasive blasting to Sa 2.5).

• Application of adhesion primer.

• Two-component high-pressure spraying.

• Layer thickness per pass up to 1000 microns; continuity is checked with a spark holiday detector.



Thermal-Insulation Installation

For flat roofs and walls:



• Bonding or mechanical fastening of thermal-insulation boards to the substrate.

• Staggered laying and joint bonding/offsetting.

• Installation of vapor barrier on the warm-air side.

• Multilayer thermal insulation with seams covered by the next layer.

• Covering with reinforced screed or lining with a slope for water drainage.



For insulation of pipelines and equipment:



• Installation of mineral-wool pipe sections with bands.

• Sealing joints with aluminum tape.

• Installation of a protective covering (galvanized steel, aluminum) for weather resistance.



Quality Control of Completed Works



For waterproofing:



1. Continuity and thickness of coating: visual inspection, thickness measurement with a probe or thickness gauge, and for polyurea, spark holiday detection.

2. Adhesion (bond strength) by pull-off or cross-cut method.

3. Watertightness check (test with water head).



For thermal insulation:



1. Actual thickness and density of the installed material.

2. Absence of misalignment, voids, and gaps.

3. Quality of sealing of joints and interfaces.

4. Moisture content of the material (not above the passport value).



Results are recorded in concealed-work inspection certificates (KS-2, KS-6a forms, as well as internal Quality Assurance Program forms).



Conclusions and Recommendations

High-quality waterproofing and thermal insulation of NPP building structures are mandatory conditions for ensuring service life and safety. It is recommended to:



1. At the design stage, specify insulation systems with a service life of at least 30-50 years, corresponding to the safety class under NP-041-22.

2. For critical zones (spent-fuel pools, pump rooms, deaerator racks), use polyurea waterproofing with thickness and continuity control.

3. For thermal insulation, give preference to non-combustible basalt-based mineral-wool boards.

4. Ensure substrate preparation in accordance with manufacturer and regulatory requirements.

5. Carry out the full quality-control cycle with preparation of concealed-work certificates.

6. For strict-regime zones, additionally verify materials for decontaminability under GOST R 51102-97 and radiation resistance.



To obtain a commercial proposal for waterproofing and thermal-insulation works at your facility (including substrate preparation, material selection, insulation installation, quality control, and handover of as-built documentation), send a technical specification indicating the type of structures, safety class, operating conditions, and required service life to the commercial department of TechAtomStroy LLC through the feedback form on the website. A cost estimate, work schedule, and technical-and-economic justification for selecting the insulation system will be prepared.



*This material was prepared on the basis of NP-041-22, NP-010-16, SP 50.13330.2012, SP 71.13330.2017, GOST 31309-2009, and GOST R 51102-97.*