Waterproofing and Thermal Insulation of NPP Buildings: Solutions for Any Safety Class

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.*