When choosing non-woven high-efficiency filters (HEPA) in the air purification system of nuclear power plants, it is necessary to take nuclear safety regulations as the core basis, and combine the special requirements of the air purification scenario such as radiation protection, aerosol control, and system stability. A comprehensive assessment should be conducted from multiple dimensions including filtration performance, structural safety, environmental adaptability, and compliance to ensure that the filters can not only meet the purification efficiency requirements but also It can also cope with the complex working conditions of nuclear power plants (such as radioactive aerosols, temperature and humidity fluctuations, long-term operating loads, etc.). The following are the specific selection dimensions and key indicators:
1. Give priority to meeting the core performance indicators of nuclear-grade filtration
The core objective of air purification in nuclear power plants is to retain radioactive aerosols (such as fission products and activation products), preventing the spread of radioactive substances into the environment or affecting the safety of equipment/personnel. Therefore, filtration performance is the primary consideration, and the following indicators should be given particular attention:
1. Give priority to meeting the core performance indicators of nuclear-grade filtration
The core objective of air purification in nuclear power plants is to retain radioactive aerosols (such as fission products and activation products), preventing the spread of radioactive substances into the environment or affecting the safety of equipment/personnel. Therefore, filtration performance is the primary consideration, and the following indicators should be given particular attention:
| Key indicators |
Nuclear-grade application requirements |
|
| Filtration efficiency | It must reach grade H13 or above (in accordance with EN 1822 standard), and some critical scenarios (such as containment exhaust, nuclear island process area) require grade H14 |
The filtration efficiency of H13 grade for aerosols with a particle size of 0.3μm is ≥99.95%, and that of H14 grade is ≥99.995%. Radioactive aerosols are mostly at the sub-micron level (0.1-1μm), and the H13/H14 level can be effectively retained to prevent “penetration leakage”. |
| Dust holding capacity | It should be significantly higher than that of ordinary industrial-grade filters (it is recommended to be ≥1000g/m², calculated specifically according to the working conditions). | The replacement cycle of nuclear power plant filters is long (in some scenarios, they need to operate continuously for several years). High dust holding capacity can reduce the replacement frequency, lower the risk of shutdown and the generation of radioactive waste (the replaced filters are radioactive waste and require special treatment). |
| Resistance characteristic | The initial resistance is ≤250Pa (at rated air volume), and the final resistance is ≤450Pa | Low initial resistance can reduce the energy consumption of the fan and prevent the system air pressure from being too high. The final resistance must match the air pressure of the fan in the purification system to ensure the stability of the system air volume throughout the service life of the filter (fluctuations in air volume will affect the purification effect). |
Second, enhance the nuclear safety compatibility of structures and materials
The air purification system of a nuclear power plant may be exposed to conditions such as temperature and humidity fluctuations, chemical corrosion, vibration and shock (such as earthquakes, equipment start-up and shutdown), and once the filter is damaged, it may lead to radioactive leakage. Therefore, structural integrity and material stability are of vital importance.
1. Filter material selection: Special materials with radiation resistance and low precipitation are preferred
Core filter material: Glass fiber filter material (rather than ordinary synthetic fiber) must be selected. The reason is:
Glass fiber has excellent radiation resistance (capable of withstanding a γ radiation dose of ≥10⁵Gy, far exceeding the 5×10³Gy of synthetic fibers), preventing the degradation of filter materials and the decline in efficiency under long-term radiation.
The pore size of glass fiber is uniform, and its retention rate for sub-micron radioactive aerosols is stable. Moreover, it is less likely to experience “pore size expansion” due to humidity changes (the humidity in nuclear power plants often reaches 60%-80%).
Auxiliary materials: Sealant and frame materials must meet the requirements of “low radioactivity adsorption, temperature resistance and corrosion resistance”.
– Sealant: Choose silicone or fluororubber sealants (temperature resistance -40 ℃ to 200℃, resistant to weakly acidic gases in nuclear island environments), and avoid using ordinary nitrile rubber (prone to aging, release of organic matter and adsorption of radioactive substances).
– Frame: Aluminum alloy or stainless steel frames are preferred (aluminum alloy is lightweight and stainless steel is corrosion-resistant, neither adsorbing radioactive substances). Galvanized steel frames are strictly prohibited (zinc is easily activated by radiation, generating secondary radioactivity).
2. Structural design: Ensure “zero leakage” and impact resistance
Optimization of the non-partition structure: “hot melt adhesive spacer bars” are adopted to replace the traditional aluminum partitions (the non-partition design can reduce the dead corners of air flow and prevent radioactive aerosols from accumulating in the gaps of the partitions), and the spacer bars need to be continuously formed without any breaks to ensure the uniform unfolding of the filter material and avoid damage to the filter material due to excessively high local wind speed.
Sealing design The sealing between the filter and the installation frame should adopt a “double-seal” (such as a “groove + gasket” structure), with the gasket material being closed-cell sponge or silicone rubber (compression ratio ≥30% to ensure that the seal does not fail during long-term operation), to avoid “bypass leakage” caused by poor sealing (bypass leakage will allow unfiltered air to directly enter the downstream, causing radiation risks).
Impact resistance performance: The filter must pass seismic simulation tests (in accordance with GB 50267 “Code for Seismic Design of Nuclear Power Plants”, withstanding an acceleration of 0.3g to 0.5g) and “wind pressure fluctuation tests” (enduring an instantaneous wind pressure of 120% of the rated air volume) to ensure that the filter material does not fall off and the frame does not deform under extreme working conditions.
Iii. Match the specific application scenarios and requirements of nuclear power plants
The air purification targets for different areas of a nuclear power plant (nuclear island, conventional island, and auxiliary building) vary, and customized filters should be selected based on the characteristics of the scenarios.
The air purification system of a nuclear power plant may be exposed to conditions such as temperature and humidity fluctuations, chemical corrosion, vibration and shock (such as earthquakes, equipment start-up and shutdown), and once the filter is damaged, it may lead to radioactive leakage. Therefore, structural integrity and material stability are of vital importance.
1. Filter material selection: Special materials with radiation resistance and low precipitation are preferred
Core filter material: Glass fiber filter material (rather than ordinary synthetic fiber) must be selected. The reason is:
Glass fiber has excellent radiation resistance (capable of withstanding a γ radiation dose of ≥10⁵Gy, far exceeding the 5×10³Gy of synthetic fibers), preventing the degradation of filter materials and the decline in efficiency under long-term radiation.
The pore size of glass fiber is uniform, and its retention rate for sub-micron radioactive aerosols is stable. Moreover, it is less likely to experience “pore size expansion” due to humidity changes (the humidity in nuclear power plants often reaches 60%-80%).
Auxiliary materials: Sealant and frame materials must meet the requirements of “low radioactivity adsorption, temperature resistance and corrosion resistance”.
– Sealant: Choose silicone or fluororubber sealants (temperature resistance -40 ℃ to 200℃, resistant to weakly acidic gases in nuclear island environments), and avoid using ordinary nitrile rubber (prone to aging, release of organic matter and adsorption of radioactive substances).
– Frame: Aluminum alloy or stainless steel frames are preferred (aluminum alloy is lightweight and stainless steel is corrosion-resistant, neither adsorbing radioactive substances). Galvanized steel frames are strictly prohibited (zinc is easily activated by radiation, generating secondary radioactivity).
2. Structural design: Ensure “zero leakage” and impact resistance
Optimization of the non-partition structure: “hot melt adhesive spacer bars” are adopted to replace the traditional aluminum partitions (the non-partition design can reduce the dead corners of air flow and prevent radioactive aerosols from accumulating in the gaps of the partitions), and the spacer bars need to be continuously formed without any breaks to ensure the uniform unfolding of the filter material and avoid damage to the filter material due to excessively high local wind speed.
Sealing design The sealing between the filter and the installation frame should adopt a “double-seal” (such as a “groove + gasket” structure), with the gasket material being closed-cell sponge or silicone rubber (compression ratio ≥30% to ensure that the seal does not fail during long-term operation), to avoid “bypass leakage” caused by poor sealing (bypass leakage will allow unfiltered air to directly enter the downstream, causing radiation risks).
Impact resistance performance: The filter must pass seismic simulation tests (in accordance with GB 50267 “Code for Seismic Design of Nuclear Power Plants”, withstanding an acceleration of 0.3g to 0.5g) and “wind pressure fluctuation tests” (enduring an instantaneous wind pressure of 120% of the rated air volume) to ensure that the filter material does not fall off and the frame does not deform under extreme working conditions.
Iii. Match the specific application scenarios and requirements of nuclear power plants
The air purification targets for different areas of a nuclear power plant (nuclear island, conventional island, and auxiliary building) vary, and customized filters should be selected based on the characteristics of the scenarios.
| Application scenarios | Core requirements | Key points for filter selection |
| Nuclear island process areas (such as reactor buildings, fuel buildings | Intercept radioactive aerosols (such as ¹³⁷Cs, ¹³¹I) to prevent their spread to equipment or personnel areas |
– Efficiency grade: H14 (ensuring a retention rate of radioactive aerosols of ≥99.995%); – Radiation resistance: The radiation tolerance dose of the filter material is ≥10⁵Gy; – Temperature resistance: Can withstand 40℃ to 60℃ (the temperature in the nuclear island process area is relatively high). |
| Containment exhaust system | In accident conditions (such as water loss accidents), high-concentration radioactive aerosols should be intercepted to prevent their discharge into the environment |
– Efficiency grade: H14 + Post-activated carbon layer (activated carbon adsorbs radioactive iodine to prevent iodine vapor from penetrating); – Structure: It adopts a “high-pressure resistant design” (the containment pressure can reach 0.5MPa), and the frame is made of stainless steel. – Dust holding capacity: ≥1500g/m² (A large amount of aerosol may be generated after an accident and needs to be retained for a long time). |
| Conventional island and auxiliary factory buildings | Remove dust and microorganisms to prevent contamination of equipment (such as steam turbines and electrical cabinets), and there is no risk of radioactivity |
– Efficiency grade: H13 (Meeting the general high-efficiency purification requirements and reducing costs); – Temperature resistance: Can withstand 30℃ to 40℃ (the temperature on the conventional island is relatively low); – Moisture-proofing: The filter material needs to undergo “hydrophobic coating treatment” (the humidity in the conventional island is relatively high, to prevent the filter material from absorbing moisture and getting moldy). |
4. Strictly verify compliance and supplier qualifications
Nuclear power plants belong to a special industry. The “compliance” of filters is the bottom line of safety. The following documents and qualifications need to be verified with emphasis:
Nuclear-grade product certification
– Must possess nuclear-grade product qualifications recognized by the National Nuclear Safety Administration (NNSA) (such as the “Design and Manufacture License for Nuclear-Grade Air Filters”), or pass international nuclear-grade certifications (such as ASME QNA-1 of the United States, RCC-M standard certifications of France);
– Provide the “Radioactive Leakage Test Report” of the product (in accordance with the requirements of GB/T 13554 “High Efficiency Air Filters”, the overall leakage rate at the rated air volume is ≤0.01%).
Supplier Capability Verification
Suppliers are required to have “Nuclear-grade Product Production System Certification” (such as ISO 9001 + special requirements of the nuclear industry), and have at least 3 application cases of similar products in nuclear power plants (operating time ≥5 years, no safety accidents);
You can request the supplier to provide a “batch test Report of Filter Materials” (the efficiency, resistance and radiation resistance of each batch of filter materials all need to be sampled and tested) to avoid performance non-compliance due to batch differences of filter materials.
Compatibility of decommissioning and waste treatment:
The filter should be designed as an “easy-to-disassemble and easy-to-cure” structure (such as the frame and filter material can be separated, and the filter material is an integral type, which is convenient for subsequent installation in a concrete container for curing).
The materials must meet the “low-level waste Classification Requirements” (for example, the metal frame can be cleaned and recycled, and the filter material should be non-combustible to avoid secondary pollution caused by incineration).
V. Summary: Select processes and Key Control Points
Clarify the scene requirements: First, determine the application area of the filter (nuclear island/conventional island), the air volume to be processed, and the radioactive level, and clarify the core indicators such as efficiency (H13/H14), temperature resistance, and radiation resistance;
2. Screen compliant suppliers: Give priority to suppliers with nuclear-grade qualifications and mature cases, and exclude manufacturers that only have the production capacity of ordinary industrial filters;
3. Sample performance testing: Conduct sampling tests on candidate products (with a focus on filtration efficiency, leakage rate, and dust holding capacity), and if necessary, entrust a third-party nuclear-grade testing institution (such as China Institute of Atomic Energy) for verification.
4. The contract clearly stipulates: In the procurement contract, terms such as “nuclear grade qualification, batch testing, and support for decommissioning treatment” should be clearly defined to ensure that the supplier assumes full quality responsibility throughout the process.
Through strict screening in the above dimensions, it can be ensured that the non-woven high-efficiency filter not only meets the safety requirement of “efficiently retaining radioactive substances” in the air purification of nuclear power plants, but also can adapt to long-term and complex operating conditions, providing reliable guarantees for nuclear safety.
Nuclear power plants belong to a special industry. The “compliance” of filters is the bottom line of safety. The following documents and qualifications need to be verified with emphasis:
Nuclear-grade product certification
– Must possess nuclear-grade product qualifications recognized by the National Nuclear Safety Administration (NNSA) (such as the “Design and Manufacture License for Nuclear-Grade Air Filters”), or pass international nuclear-grade certifications (such as ASME QNA-1 of the United States, RCC-M standard certifications of France);
– Provide the “Radioactive Leakage Test Report” of the product (in accordance with the requirements of GB/T 13554 “High Efficiency Air Filters”, the overall leakage rate at the rated air volume is ≤0.01%).
Supplier Capability Verification
Suppliers are required to have “Nuclear-grade Product Production System Certification” (such as ISO 9001 + special requirements of the nuclear industry), and have at least 3 application cases of similar products in nuclear power plants (operating time ≥5 years, no safety accidents);
You can request the supplier to provide a “batch test Report of Filter Materials” (the efficiency, resistance and radiation resistance of each batch of filter materials all need to be sampled and tested) to avoid performance non-compliance due to batch differences of filter materials.
Compatibility of decommissioning and waste treatment:
The filter should be designed as an “easy-to-disassemble and easy-to-cure” structure (such as the frame and filter material can be separated, and the filter material is an integral type, which is convenient for subsequent installation in a concrete container for curing).
The materials must meet the “low-level waste Classification Requirements” (for example, the metal frame can be cleaned and recycled, and the filter material should be non-combustible to avoid secondary pollution caused by incineration).
V. Summary: Select processes and Key Control Points
Clarify the scene requirements: First, determine the application area of the filter (nuclear island/conventional island), the air volume to be processed, and the radioactive level, and clarify the core indicators such as efficiency (H13/H14), temperature resistance, and radiation resistance;
2. Screen compliant suppliers: Give priority to suppliers with nuclear-grade qualifications and mature cases, and exclude manufacturers that only have the production capacity of ordinary industrial filters;
3. Sample performance testing: Conduct sampling tests on candidate products (with a focus on filtration efficiency, leakage rate, and dust holding capacity), and if necessary, entrust a third-party nuclear-grade testing institution (such as China Institute of Atomic Energy) for verification.
4. The contract clearly stipulates: In the procurement contract, terms such as “nuclear grade qualification, batch testing, and support for decommissioning treatment” should be clearly defined to ensure that the supplier assumes full quality responsibility throughout the process.
Through strict screening in the above dimensions, it can be ensured that the non-woven high-efficiency filter not only meets the safety requirement of “efficiently retaining radioactive substances” in the air purification of nuclear power plants, but also can adapt to long-term and complex operating conditions, providing reliable guarantees for nuclear safety.
