Floors, Screeds, and Linings for Nuclear Power Plants: Acid Resistance, Decontamination, and a 50+ Year Service Life
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.
• 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.*