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.
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).*
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).*