{"id":4551,"date":"2025-09-12T08:52:19","date_gmt":"2025-09-12T00:52:19","guid":{"rendered":"https:\/\/www.bacintl.com\/?p=4551"},"modified":"2025-09-12T08:52:19","modified_gmt":"2025-09-12T00:52:19","slug":"safety-assurance-of-non-partitioned-high-efficiency-filters-in-nuclear-power-plant-air-purification","status":"publish","type":"post","link":"https:\/\/www.bacintl.com\/es\/safety-assurance-of-non-partitioned-high-efficiency-filters-in-nuclear-power-plant-air-purification\/","title":{"rendered":"Garant\u00eda de seguridad de los filtros de alta eficacia no compartimentados en la purificaci\u00f3n del aire de las centrales nucleares"},"content":{"rendered":"
In the air purification system of nuclear power plants, the non-woven high-efficiency filter (HEPA filter) is essential for ensuring air quality and preventing the spread of radioactive aerosols. Safety assurance must encompass all stages, including design, materials, performance, installation, operation, maintenance, and emergency response. The core goal is to ensure the filter effectively retains radioactive particles under both normal and accident conditions (such as LOCA or water loss), thus protecting the environment and personnel. The following is an analysis of its security system across six core dimensions:
\nI. Design Safety: Special structural design adapted to the nuclear environment
\nThe design of high-efficiency filters without separators for nuclear power plants needs to break through the conventional industrial filter standards and be specially optimized for extreme conditions such as high radiation, high humidity, and potential high temperatures (accident conditions) in nuclear facilities. The core design guarantees include:
\nBalanced design of airflow resistance and dust holding capacity
\nAdopting a low-resistance “V-shaped” or “W-shaped” pleated structure (with a filtration area increased by 3 to 5 times compared to the flat type), it ensures air volume (usually adapted to the air volume requirements of the nuclear island ventilation system, with a single unit air volume reaching 1000 to 3000 m\u00b3\/h) while reducing system energy consumption.
\nThe pleat spacing is precisely controlled (usually 2-3mm) to prevent unfiltered air from directly penetrating due to air flow short circuits. At the same time, sufficient dust-holding space is reserved to ensure the stable performance of the filter throughout its entire service life (usually 1-3 years under normal operating conditions), without sudden increase in resistance or structural damage caused by rapid dust accumulation.
\nStructural strength design for resisting extreme working conditions
\nFrames are made of aluminum alloy or stainless steel to prevent rust and deformation in humid nuclear environments. The bond between frame and filter material uses high-temperature and radiation-resistant sealants to maintain integrity in accident conditions (up to 150-200\u2103, nearly 100% humidity).
\nThe filter material support layer adopts high-strength glass fiber mesh or metal mesh to prevent the filter material from tearing or wrinkling under high air flow impact (such as the start and stop of the ventilation system or air flow disturbance in an accident), ensuring the integrity of the filtration structure.
\nSealing design: Zero leakage core guarantee
\nThe sealing surface between the filter and the installation frame adopts polyurethane foam rubber strips (with good elasticity, radiation resistance and not easy to age), and the compression amount of the rubber strips is controlled at 30%-50% to ensure that there is no gap on the sealing surface.
\nThe filters in some key areas (such as the nuclear reactor building and the radioactive waste treatment room) adopt a “double-seal structure” (main seal + backup seal). Even if the main seal fails due to aging or installation deviation, the backup seal can still prevent the leakage of radioactive aerosols.
\nHaving discussed design and sealing, the next dimension is material safety, emphasizing the selection of nuclear-grade materials with radiation and aging resistance.
\nThe material properties of the filter directly determine its long-term stability in the nuclear environment. All materials must pass nuclear-grade material certification (such as NRC certification in the United States and HAF certification in China). The core material requirements are as follows:<\/div>\n
\n\n\n\n\n\n\n\n
\n

Material components<\/p>\n<\/td>\n

Material requirements<\/td>\nSafety function<\/td>\n<\/tr>\n
Filter material<\/td>\nSuperfine glass fiber (diameter 0.5-2\u03bcm) or PTFE-coated glass fiber<\/td>\nIt can retain radioactive particles of \u22650.3\u03bcm (such as aerosols of fission products Cs-137 and Sr-90), with a filtration efficiency of \u226599.97%<\/td>\n<\/tr>\n
Framework<\/td>\n5052 aluminum alloy (corrosion-resistant) or 304 stainless steel (high-temperature resistant, radiation-resistant)<\/td>\nSupport the filter material structure to prevent the frame from becoming brittle or deformed in a high-radiation environment<\/td>\n<\/tr>\n
Sealant\/strip<\/td>\n\n

Radiation-resistant silicone sealant (performance remains unchanged when radiation dose \u226410\u2076 Gy), closed-cell polyurethane rubber strip (temperature resistance -30 to 200\u2103)<\/p>\n<\/td>\n

Ensure the seal between the filter and the installation frame to avoid “bypass leakage” (the leakage rate should be \u22640.1%).<\/td>\n<\/tr>\n
Separator (without partition)<\/td>\nHot melt adhesive lines (radiation-resistant and non-volatile organic compound release) or aluminum foil separator strips<\/td>\nMaintain the spacing between the pleats of the filter material to prevent the pleats from sticking together, which could lead to a reduction in the filtration area<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
Key materials must pass radiation resistance tests: under gamma-ray or neutron radiation (dose simulation of the cumulative radiation during the design life of a nuclear power plant), the attenuation rate of mechanical properties (such as tensile strength, elasticity) and filtration performance (efficiency, resistance) of the materials should be \u226410%, and no toxic substances (such as formaldehyde, heavy metals) should be released.<\/div>\n
\"\"
\nIii. Performance Safety: Strict nuclear-level certification and testing standards
\nThe non-woven high-efficiency filters used in nuclear power plants must meet the specific standards for the nuclear industry (rather than the ordinary industrial HEPA standards). The core performance tests and certifications include:
\nTesting of filtration efficiency and leakage rate
\nDOP\/PAO scanning test (international standard ISO 14644-3) : Use 0.3\u03bcm DOP (dioctylphthalate) or PAO (polyalpha-olefin) aerosol, and conduct a full surface scan of the “filter material surface + sealing surface + frame seam” of the filter through a laser particle counter. Requirements:
\nThe efficiency of the filter material area is \u226599.97% (for 0.3\u03bcm particles).
\nThe leakage rate of the sealed area is \u22640.1% (i.e., the proportion of the leaked aerosol volume to the total intake volume is \u22640.1%), and the leakage concentration at a single leakage point is \u22640.01 mg\/m\u00b3 (radioactive aerosol control threshold).
\nTemperature resistance, moisture resistance and chemical resistance tests
\nTemperature resistance test: Continuously operate at 150\u2103 (simulating the high temperature after a LOCA accident) for 24 hours. After cooling, the efficiency decline is \u22645%, and there is no structural damage.
\nMoisture resistance test: After continuous operation for 7 days in an environment of 95% relative humidity and 40\u2103, the resistance change rate is \u226415%, and there is no mold on the filter material or rust on the frame.
\nChemical resistance test: It can withstand the chemical substances that may exist in nuclear power plants (such as boric acid solution droplets, ammonia vapor), and there is no significant decrease in the strength and efficiency of the filter material after immersion.
\nNuclear-level certification
\nIt must pass the nuclear-grade equipment certification of the National Nuclear Safety Administration (NNSA) (China HAF 604 standard) or the safety certification of the International Atomic Energy Agency (IAEA) to prove that it complies with the “defense in depth” principle of nuclear facilities and can serve as the “second barrier” for the spread of radioactive substances (the first barrier is the equipment casing\/factory building wall).
\nIv. Installation Safety: Precise Construction and Leakage Control
\nEven if the filter itself is qualified in performance, improper installation may still lead to “bypass leakage”. Therefore, the installation process must follow nuclear-grade construction standards (such as the relevant provisions in China’s GB 50235-2010 “Code for Construction of Industrial Metal Pipeline Engineering”). Core safeguard measures:
\nPre-treatment before installation
\nThe installation area (such as ventilation ducts, filter static pressure boxes) needs to undergo cleanliness testing: ensure there is no dust, welding slag, or metal debris (to prevent foreign objects from scratching the filter material after installation), and the concentration of air suspended particles should be \u22641000 particles \/m\u00b3 (above 0.5\u03bcm).
\nBefore opening the filter box, it is necessary to check the integrity of the packaging (to prevent damage to the filter material during transportation). After opening the box, a preliminary check of the filter material for holes or wrinkles should be conducted by the “light transmission method”.
\nPrecise positioning and sealed installation
\nThe installation is carried out by the “horizontal hoisting + guide rod positioning” method (to avoid uneven force on the filter material during manual handling), ensuring that the filter is completely aligned with the sealing surface of the installation frame, with a deviation of no more than 1mm.
\nAfter the sealing gasket is installed, a “pressure test” is required: Compressed air (at a pressure of 0.1MPa) is introduced into the gap between the filter and the frame. If no bubbles are produced by the bubble detector, it indicates that the seal is qualified.
\nOverall test after installation
\nConduct an “aerosol challenge test” on the entire air purification system (including filters, air ducts, and fans) : Inject simulated radioactive aerosols (such as Eu-152 aerosol) into the system, and measure the aerosol concentration at the system outlet. The retention efficiency should be \u226599.99% to ensure no system-level leakage.
\nV. Operation and Maintenance Security: Performance Monitoring and Replacement throughout the entire lifecycle
\nThe operation and maintenance of nuclear power plant filters need to establish a digital management system. Through real-time monitoring and regular inspection, it is ensured that they remain in a safe state throughout their life cycle.
\nReal-time performance monitoring
\nDifferential pressure transmitters (with an accuracy of \u00b10.1Pa) are installed at the front and rear ends of the filter to monitor resistance changes in real time. When the resistance exceeds twice the initial resistance (or reaches the design upper limit, such as 500Pa), the system will automatically alarm and prompt that the filter needs to be replaced (to avoid excessive resistance causing fan overload or filter material damage).
\nRadioactive aerosol monitors (with a detection limit of \u22641\u00d710\u207b\u00b9\u00b2 Bq\/m\u00b3) are installed at the filter outlets in key areas (such as the reactor containment vessel). If an abnormal increase in radioactive concentration is detected, emergency procedures (such as closing the air duct and activating the backup purification system) will be triggered immediately.
\nRegular inspection and maintenance
\nConduct a “DOP scan retest” every six months: Focus on checking whether the sealing surface has leaked due to aging or vibration. If the leakage rate exceeds 0.1%, the sealing gasket or filter needs to be replaced.
\nConduct a “filter material integrity check” once a year: Observe through an endoscope whether the filter material is damaged or wrinkled. If any defects are found, replace it immediately (to avoid radioactive leakage due to filter material damage).
\nFilter replacement and disposal safety
\nWhen replacing the filter, it should be carried out in a negative pressure glove box or “isolation area” (to prevent the operator from coming into contact with the filter that may be attached with radioactive substances). The replacement personnel need to wear nuclear-grade protective clothing (such as Tyvek protective clothing) and respiratory protective equipment.
\nThe replaced waste filters need to be treated as radioactive solid waste: first, they should undergo “fixation treatment” (such as being placed in stainless steel containers and filled with concrete), then be transported to the radioactive waste storage facility of the nuclear power plant for temporary storage, and finally be disposed of in accordance with national regulations (such as deep burial disposal) to prevent the secondary diffusion of radioactive substances.
\nVi. Emergency Safety: Redundant Assurance in Accident Conditions
\nIn the design of nuclear power plants, the principle of “defense in depth” should be taken into account. The filter system needs to have emergency response capabilities to ensure that it can still play a safe role under accident conditions.
\nRedundant configuration
\nThe key systems (such as the containment ventilation system) adopt a “one in use and one on standby” or “N+1” redundant design: during normal operation, one filter works while the rest are on standby. If the working filter fails, the backup filter can be automatically put into operation within 10 seconds to ensure that the purification system is not interrupted.
\nAdaptability to accident conditions
\nFor LOCA incidents (water loss incidents), the filter must be able to withstand “high-temperature and high-pressure water vapor impact” : By installing a “steam-water separator” at the front end of the filter, most of the liquid water is removed first, and then “high-temperature resistant filter material” is used to retain aerosols, ensuring that the filtration efficiency can still be maintained at \u226599.97% within one hour after the incident.
\nFor “fire accidents”, the filter must have flame-retardant performance: the oxygen index of the filter material and the frame material should be \u226532 (non-combustible material standard), to prevent the filter from burning and generating toxic gases or structural collapse during a fire, which could affect system safety.
\nEmergency response procedure
\nIf severe leakage from the filter is detected (such as when the radioactive concentration exceeds the standard by more than ten times), immediately activate the “system isolation procedure” : close the electric air valves at the front and rear ends of the filter to cut off the airflow in this air duct, and simultaneously activate the “emergency purification system” (such as a mobile high-efficiency filtration device) to prevent the further spread of radioactive substances.
\nAfter an accident, a “comprehensive assessment” of the filter system is required: check the structural integrity, filtration efficiency and the degree of radioactive contamination of the filter, determine whether replacement or repair is needed, and ensure that there are no safety hazards before the system returns to normal operation.
\nResumen
\nThe safety guarantee of the non-woven high-efficiency filter in nuclear power plants is a “multi-dimensional, full-chain” system. Its core logic is to build the filter into the “last line of defense” for air purification in nuclear facilities through design adaptability, material reliability, performance stability, installation accuracy, operation and maintenance controllability and emergency redundancy. This system not only needs to meet the strict standards of the nuclear industry, but also needs to further enhance its safety redundancy under extreme working conditions through continuous technological iterations (such as developing more radiation-resistant PTFE-coated filter materials and more intelligent digital monitoring systems), providing key support for the safe operation of nuclear power plants.<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

In the air purification system of nuclear power plants, the non-woven high-efficiency filter (HEPA filter) is essential for ensuring air quality and preventing the spread of radioactive aerosols. Safety assurance must encompass all stages, including design, materials, performance, installation, operation, maintenance, and emergency response. The core goal is to ensure the filter effectively retains radioactive […]<\/p>","protected":false},"author":3,"featured_media":4552,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[92],"tags":[],"class_list":["post-4551","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry-technology"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/posts\/4551","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/comments?post=4551"}],"version-history":[{"count":2,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/posts\/4551\/revisions"}],"predecessor-version":[{"id":4554,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/posts\/4551\/revisions\/4554"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/media\/4552"}],"wp:attachment":[{"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/media?parent=4551"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/categories?post=4551"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bacintl.com\/es\/wp-json\/wp\/v2\/tags?post=4551"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}