This article examines the purpose and design of filter-fan modules (FFMs) as key elements of air cleanliness systems in critical areas. It analyzes regulatory requirements for equipment used in the nuclear industry, including NP-041-22, ASME AG-1 standards, and the NP-509-21 fire safety rules. It also reviews TROX solutions intended for cleanrooms and nuclear energy facilities: FFT-TC Fan Filter Unit modules, MFPCR replacement filters, and the X-CUBE CROFCU modular central air-handling unit. Technical features, selection criteria, and installation requirements for controlled-access facilities are provided.
Introduction. The Role of Filter-Fan Modules at Nuclear Power Plant Facilities
A filter-fan module (FFM) is a compact device designed to create local zones with specified air cleanliness levels. As a rule, it consists of a plenum chamber, a high-efficiency fan, a HEPA filter (High Efficiency Particulate Air) or ULPA filter (Ultra Low Penetration Air), a diffuser, and a control unit. Such modules are widely used to organize laminar airflows in cleanrooms, operating rooms, pharmaceutical manufacturing, and the nuclear industry.
At nuclear energy facilities, FFMs are used in the following critical systems:
• ventilation of glove boxes and chambers for handling radioactive materials;
• emergency filtered venting systems (Filtered Containment Venting System, FCVS);
• supply-air units for clean zones, for example areas where fuel assemblies are repaired;
• systems for maintaining the required cleanliness class in rooms with precision equipment.
The key distinguishing feature of FFM requirements at nuclear power plants is increased reliability, radiation resistance of materials, minimal outgassing, and the possibility of decontamination.
Regulatory Framework
Filtration and ventilation system equipment for the nuclear industry must comply with a set of federal rules and regulations as well as international standards.
• NP-041-22, “Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Facilities,” establishes room safety classes, which directly determine requirements for ventilation equipment.
• The rules for the design and operation of safety-related ventilation systems at nuclear power plants (new federal rules and regulations updated in 2023) apply to both designed and operating NPP ventilation systems.
• NP-509-21 and NP-511-21 establish requirements for fire safety systems, limiting the use of certain materials and methods of laying air ducts.
• ASME AG-1, “Code on Nuclear Air and Gas Treatment,” is the key international standard for components of nuclear power plant air treatment systems. It establishes requirements for the design, efficiency, qualification, and testing of high-efficiency filters for nuclear facilities.
Key Technical Requirements for FFMs in the Nuclear Industry
Equipment selection must take into account the following indicators, confirmed by testing.
Filtration Class
Safety-related systems use high-efficiency filters (HEPA) and ultra-high-efficiency filters (ULPA). Classes H14, U15, and U16 under EN 1822 retain up to 99.995–99.9999% of particles sized 0.1–0.3 μm. Nuclear installations also use filters qualified under ASME AG-1, Section FC, for axial-flow HEPA filters, which require additional reliability testing such as earthquake simulation and exposure to steam and humidity.
Tightness and Design
Filters must be equipped with a continuous flange seal or a fluid seal to prevent air bypass between the cassette and the housing. The design of the filter elements must be non-combustible and must maintain integrity under dynamic loads, including seismic impact.
Radiation Resistance
Materials used in housings and seals must not degrade under ionizing radiation. Resistance to doses of up to 10⁶ Gy is usually required. Components operated in strict-regime areas require additional confirmation of decontaminability and minimal outgassing in order to prevent contamination of technological processes.
Energy Efficiency
NPP ventilation systems are major electricity consumers. Modern fans using EC technology (electronically commutated motors) provide capacity control and low power consumption.
TROX Solutions for Filtration and Ventilation Systems
The German TROX Group supplies comprehensive solutions for ventilation, air conditioning, and air filtration. TROX products are represented in almost every country in the world, and in China the company is an accredited supplier of heating, ventilation, and air-conditioning system components for the nuclear industry of the People’s Republic of China.
Fan Filter Unit Modules (FFT-TC)
The FFT-TC series consists of ready-to-install filter-fan modules for cleanrooms. They create a top-down laminar airflow, are installed in suspended ceilings, and form a self-supporting structure.
Main technical features:
• oil-free fan with adjustable rotation speed;
• absolute filter with a fluid seal (gel seal), class H14;
• low noise and vibration levels;
• galvanized steel housing with an anti-corrosion coating.
MFPCR Filter Elements for the Nuclear Industry
The Mini Pleat Filter Panels MFPCR line consists of replacement cartridges for final filtration of supply and exhaust air. The manufacturer explicitly states their suitability for use in nuclear power applications.
Key characteristics:
• filter medium: moisture-resistant glass fiber media with thermoplastic pleat separators;
• anodized aluminum frame;
• guaranteed efficiency: H14-class HEPA filters supplied with ALC and ALG frames undergo 100% leak-detector inspection with automatic surface scanning (scan test);
• flexible adjustment of pleat geometry to minimize pressure drop.
X-CUBE CROFCU Modular Air-Handling Units
For comprehensive air preparation in cleanrooms in the nuclear industry, X-CUBE CROFCU modular central air-handling units are used. The system combines ventilation, filtration, cooling/heating, and supports cleanliness classes up to ISO 4, corresponding to Russian Class 10 under GOST R ISO 14644. The equipment is fitted with energy-efficient EC fans and is suitable for Category A/B areas (clean zones).
Installation and Quality Control Features
Work to introduce filter-fan modules at nuclear power plants must be carried out in strict compliance with work execution plans (WEPs) and the requirements of Rosatom’s unified access permit system.
Installation in Laminar Ceilings
FFT-TC modules are installed in special grid panels (tiles) of a suspended ceiling. The permissible height difference during installation must not exceed 1.0 mm per meter. Adjacent modules are joined into a frame to form a monolithic surface, preventing the bypass of unfiltered air.
Quality Control
Acceptance testing at the site must confirm the following parameters:
• filtration efficiency and continuity of the filter medium, using the scanning method for filters of class H14 and above;
• pressure drop across a clean filter and after dust loading, compared with passport data;
• airflow rate and flow velocity in the working area;
• noise level and aerosol particle concentration (0.5 μm) in accordance with ISO 14644;
• maximum pressure drop across the filter under a load of 250 Pa and higher.
For nuclear installations, qualification under ASME AG-1 is also required for air treatment system components, including leak-tightness testing after deformation (upset conditions simulation).
Special Requirements for Filter Replacement and Disposal
Spent filter-fan modules that have operated in areas with radioactive or toxic environments must be handled as solid radioactive waste (SRW). The system design must provide technical means for replacing filters without compromising circuit tightness, for example transfer containers using the “bag-in-bag” technology.
Conclusions and Recommendations
The use of certified filter-fan modules ensures the quality and reliability of cleanroom ventilation at nuclear industry facilities. TROX equipment that complies with EN 1822 and is applicable to nuclear infrastructure makes it possible to provide:
• cleanliness classes from H13 to U16, depending on the task;
• fluid sealing (gel) to ensure guaranteed tightness;
• the possibility of integration into laminar ceilings (FFT-TC modules);
• low power consumption and reduced operating costs.
Recommendations for Selecting FFMs:
1. The filter class must correspond to the design cleanliness category of the room: H14 for clean zones and U15–U16 for the most critical zones.
2. The housing and seals must be made of materials with reduced gas release and must allow decontamination, for example an anodized aluminum housing and high-hardness rubber seals.
3. For Category A rooms (clean zones), compliance with microbiological cleanliness standards must be confirmed, including verification that there is no stagnant water or hidden cavities.
4. The FFM installation design for an NPP must include a section on handling spent filters as potential radioactive waste.
To receive a commercial proposal for the design, supply, and installation of TROX filter-fan modules, including preparation of a justification for Rostechnadzor construction supervision, send the technical assignment to TechAtomStroy LLC’s commercial department via the feedback form on the website, specifying the cleanliness class, air capacity, and decontamination requirements.
*This material has been prepared using TROX data as well as the requirements of NP-041-22, ASME AG-1, and the rules for operating NPP ventilation systems.*
Introduction. The Role of Filter-Fan Modules at Nuclear Power Plant Facilities
A filter-fan module (FFM) is a compact device designed to create local zones with specified air cleanliness levels. As a rule, it consists of a plenum chamber, a high-efficiency fan, a HEPA filter (High Efficiency Particulate Air) or ULPA filter (Ultra Low Penetration Air), a diffuser, and a control unit. Such modules are widely used to organize laminar airflows in cleanrooms, operating rooms, pharmaceutical manufacturing, and the nuclear industry.
At nuclear energy facilities, FFMs are used in the following critical systems:
• ventilation of glove boxes and chambers for handling radioactive materials;
• emergency filtered venting systems (Filtered Containment Venting System, FCVS);
• supply-air units for clean zones, for example areas where fuel assemblies are repaired;
• systems for maintaining the required cleanliness class in rooms with precision equipment.
The key distinguishing feature of FFM requirements at nuclear power plants is increased reliability, radiation resistance of materials, minimal outgassing, and the possibility of decontamination.
Regulatory Framework
Filtration and ventilation system equipment for the nuclear industry must comply with a set of federal rules and regulations as well as international standards.
• NP-041-22, “Safety Requirements for Building Structures of Nuclear Power Plant Buildings and Facilities,” establishes room safety classes, which directly determine requirements for ventilation equipment.
• The rules for the design and operation of safety-related ventilation systems at nuclear power plants (new federal rules and regulations updated in 2023) apply to both designed and operating NPP ventilation systems.
• NP-509-21 and NP-511-21 establish requirements for fire safety systems, limiting the use of certain materials and methods of laying air ducts.
• ASME AG-1, “Code on Nuclear Air and Gas Treatment,” is the key international standard for components of nuclear power plant air treatment systems. It establishes requirements for the design, efficiency, qualification, and testing of high-efficiency filters for nuclear facilities.
Key Technical Requirements for FFMs in the Nuclear Industry
Equipment selection must take into account the following indicators, confirmed by testing.
Filtration Class
Safety-related systems use high-efficiency filters (HEPA) and ultra-high-efficiency filters (ULPA). Classes H14, U15, and U16 under EN 1822 retain up to 99.995–99.9999% of particles sized 0.1–0.3 μm. Nuclear installations also use filters qualified under ASME AG-1, Section FC, for axial-flow HEPA filters, which require additional reliability testing such as earthquake simulation and exposure to steam and humidity.
Tightness and Design
Filters must be equipped with a continuous flange seal or a fluid seal to prevent air bypass between the cassette and the housing. The design of the filter elements must be non-combustible and must maintain integrity under dynamic loads, including seismic impact.
Radiation Resistance
Materials used in housings and seals must not degrade under ionizing radiation. Resistance to doses of up to 10⁶ Gy is usually required. Components operated in strict-regime areas require additional confirmation of decontaminability and minimal outgassing in order to prevent contamination of technological processes.
Energy Efficiency
NPP ventilation systems are major electricity consumers. Modern fans using EC technology (electronically commutated motors) provide capacity control and low power consumption.
TROX Solutions for Filtration and Ventilation Systems
The German TROX Group supplies comprehensive solutions for ventilation, air conditioning, and air filtration. TROX products are represented in almost every country in the world, and in China the company is an accredited supplier of heating, ventilation, and air-conditioning system components for the nuclear industry of the People’s Republic of China.
Fan Filter Unit Modules (FFT-TC)
The FFT-TC series consists of ready-to-install filter-fan modules for cleanrooms. They create a top-down laminar airflow, are installed in suspended ceilings, and form a self-supporting structure.
Main technical features:
• oil-free fan with adjustable rotation speed;
• absolute filter with a fluid seal (gel seal), class H14;
• low noise and vibration levels;
• galvanized steel housing with an anti-corrosion coating.
MFPCR Filter Elements for the Nuclear Industry
The Mini Pleat Filter Panels MFPCR line consists of replacement cartridges for final filtration of supply and exhaust air. The manufacturer explicitly states their suitability for use in nuclear power applications.
Key characteristics:
• filter medium: moisture-resistant glass fiber media with thermoplastic pleat separators;
• anodized aluminum frame;
• guaranteed efficiency: H14-class HEPA filters supplied with ALC and ALG frames undergo 100% leak-detector inspection with automatic surface scanning (scan test);
• flexible adjustment of pleat geometry to minimize pressure drop.
X-CUBE CROFCU Modular Air-Handling Units
For comprehensive air preparation in cleanrooms in the nuclear industry, X-CUBE CROFCU modular central air-handling units are used. The system combines ventilation, filtration, cooling/heating, and supports cleanliness classes up to ISO 4, corresponding to Russian Class 10 under GOST R ISO 14644. The equipment is fitted with energy-efficient EC fans and is suitable for Category A/B areas (clean zones).
Installation and Quality Control Features
Work to introduce filter-fan modules at nuclear power plants must be carried out in strict compliance with work execution plans (WEPs) and the requirements of Rosatom’s unified access permit system.
Installation in Laminar Ceilings
FFT-TC modules are installed in special grid panels (tiles) of a suspended ceiling. The permissible height difference during installation must not exceed 1.0 mm per meter. Adjacent modules are joined into a frame to form a monolithic surface, preventing the bypass of unfiltered air.
Quality Control
Acceptance testing at the site must confirm the following parameters:
• filtration efficiency and continuity of the filter medium, using the scanning method for filters of class H14 and above;
• pressure drop across a clean filter and after dust loading, compared with passport data;
• airflow rate and flow velocity in the working area;
• noise level and aerosol particle concentration (0.5 μm) in accordance with ISO 14644;
• maximum pressure drop across the filter under a load of 250 Pa and higher.
For nuclear installations, qualification under ASME AG-1 is also required for air treatment system components, including leak-tightness testing after deformation (upset conditions simulation).
Special Requirements for Filter Replacement and Disposal
Spent filter-fan modules that have operated in areas with radioactive or toxic environments must be handled as solid radioactive waste (SRW). The system design must provide technical means for replacing filters without compromising circuit tightness, for example transfer containers using the “bag-in-bag” technology.
Conclusions and Recommendations
The use of certified filter-fan modules ensures the quality and reliability of cleanroom ventilation at nuclear industry facilities. TROX equipment that complies with EN 1822 and is applicable to nuclear infrastructure makes it possible to provide:
• cleanliness classes from H13 to U16, depending on the task;
• fluid sealing (gel) to ensure guaranteed tightness;
• the possibility of integration into laminar ceilings (FFT-TC modules);
• low power consumption and reduced operating costs.
Recommendations for Selecting FFMs:
1. The filter class must correspond to the design cleanliness category of the room: H14 for clean zones and U15–U16 for the most critical zones.
2. The housing and seals must be made of materials with reduced gas release and must allow decontamination, for example an anodized aluminum housing and high-hardness rubber seals.
3. For Category A rooms (clean zones), compliance with microbiological cleanliness standards must be confirmed, including verification that there is no stagnant water or hidden cavities.
4. The FFM installation design for an NPP must include a section on handling spent filters as potential radioactive waste.
To receive a commercial proposal for the design, supply, and installation of TROX filter-fan modules, including preparation of a justification for Rostechnadzor construction supervision, send the technical assignment to TechAtomStroy LLC’s commercial department via the feedback form on the website, specifying the cleanliness class, air capacity, and decontamination requirements.
*This material has been prepared using TROX data as well as the requirements of NP-041-22, ASME AG-1, and the rules for operating NPP ventilation systems.*