GB/T 22158-2021 Code for fire protection design of nuclear power plant
1 Scope
This document specifies the basic requirements for internal fire protection and explosion protection design of nuclear power plant, mainly including general requirements for fire protection design, fire protection design of general layout, fire prevention and fire spread restriction, fire evacuation, automatic fire alarm system, fire water supply and fire extinguishing system, ventilation, fire protection, smoke prevention and exhaust, fire safety analysis, internal explosion protection design, and fire protection design requirements for key areas and equipment.
This document is applicable to the design of newly built onshore stationary thermal neutron reactor nuclear power plants in China, and may serve as a reference for the design of other types of nuclear power plants and nuclear facilities.
This document is mainly aimed at the internal fire protection and explosion protection design of important buildings and structures for nuclear safety (such as nuclear island plant buildings, as well as pump rooms and tunnels of important plant water systems). In addition to the requirements in Clauses 4, 5 and 13 (except for the requirements specifically referring to nuclear safety important building and structure), the fire protection design of conventional island and supporting plant buildings shall also meet the requirements of other relevant Chinese design standards.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 18380 (all parts) Tests on electric and optical fibre cables under fire conditions
GB/T 19216 (all parts) Circuit integrity test for electric cables or optical fiber cables under fire conditions
GB/T 40620 Guidelines for fire hazard analyses in nuclear power plants
GB 50016 Code for fire protection design of buildings
GB 50058 Code for design of electrical installations in explosive atmospheres
GB 50084 Code for design of sprinkler systems
GB 50140 Code for design of extinguisher distribution in buildings
GB 50151 Code for design of foam extinguishing systems
GB 50219 Technical code for water spray fire protection systems
GB/T 50294 Design code for general plan and transportation of nuclear power plants
GB 50745 Code for design of fire protection for conventional island in nuclear power plants
GB 50974 Code of design on fire protection water supply and hydrant systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
fire retardant
property of an object to extinguish, reduce or significantly retard the combustion of certain materials
3.2
fire area
plant building or part of a plant building constructed to prevent the spread of a fire within a specified time. The fire area may consist of one or more rooms, of which, all boundaries shall be all surrounded by fire barriers
3.3
fire zone
zone equipped with fire protection facilities (such as limiting the amount of combustible materials, space separation, fixed fire extinguishing system, fire coating, or other facilities) to separate the fire, which will protect the separated system from significant damage
3.4
fire load
total amount of heat that could be released by the combustion of all combustible materials in a space
Note: It is expressed in megajoule (MJ).
3.5
fire load density
fire load of a defined space, calculated per unit floor area
Note: It is expressed in megajoule per square meter (MJ/m2).
3.6
fire duration time
combustion time for a defined space, given that all combustibles are completely consumed and assuming no fire suppression intervention during the process
Note: It is expressed in minute (min) or hour (h).
3.7
fire damper
damper installed in the supply or return duct of ventilation and air conditioning system, or on the fire boundary, which is normally open and closes automatically when the smoke temperature in the duct or at the boundary reaches a set value, or is closed by a fire control system, and can meet the requirements of air leakage and fire resistance integrity within a certain period of time, and plays a role of smoke insulation and fire retardance
3.8
fire barrier
barrier designed to prevent the spread of fire to adjacent areas and possessing a specified fire resistance rating, including walls, floors, ceilings, fire-proof air duct, or closure devices (such as fire doors, fire dampers, fire-proof seals and fire penetrations) in door openings, penetrations and ventilation systems
3.9
fire-related common mode failure
consequences of simultaneous loss of multiple series of systems, components and cables performing the same nuclear safety function due to fire
3.10
evacuation passageway
evacuation passageways such as corridors, passages, staircases and exits mainly used for evacuation of people in case of fire
3.11
smoke-proof staircase
staircase with a pressurized air supply system inside or with a smoke-proof anteroom, open balcony, or recessed gallery at its entrance, with all doors leading to the anteroom and staircase being fire doors, so as to prevent the ingress of smoke and hot gas during a fire
3.12
protected evacuation passageway
enclosed staircase or smoke-proof staircase which is divided into separate fire areas/fire zones to prevent the intrusion of fire and smoke and ensure the safety evacuation of people in case of fire, as well as main evacuation passageway
Note: The outdoor area of the plant building is also considered as a protected evacuation passageway.
3.13
nuclear safety important building and structure
building and structure containing nuclear safety important items (systems and components)
3.14
passive fire resistant protection structure
supplementary fire protection structure for certain equipment or cables, which is deemed as necessary through fire safety analysis to ensure the safety functions of the unit in the event of a fire, including fire-resistant wrapping for cable tray section, fire cabinet and fire barrier
3.15
fire local mimic panel
fire local mimic panel cabinet installed at the entrance or all floors of nuclear safety-related plant buildings, with mimic floor plans and indicator lights, which are used to operate and control the fire protection system equipment in the area, and provide fire alarm
3.16
post-fire safe-shutdown components
equipment and cables needed to achieve and maintain a safe shutdown after a fire
3.17
fire hazard analysis; FHA
analysis that evaluates the potential impact of a hypothetical fire within each fire area/fire zone on safety important items to verify that the fire protection design satisfies the three major nuclear safety objectives, including the reliability of fire resistance rating of fire barriers, the design adequacy of fire extinguishing systems and automatic alarm systems
3.18
fire vulnerability analysis; FVA
analysis designed to comprehensively and systematically solve and deal with fire-related common mode failure, which involves the following steps: carry out identification for each fire area/fire zone, and then carry out functional analysis and fire risk analysis on the common mode points, and take supplementary fire protection measures at the common mode points confirmed to be unacceptable after analysis, so as to ensure that no necessary safety functions of the unit will be lost due to common mode failure in case of fire, thus realizing the nuclear safety objectives
3.19
post-fire safe-shutdown analysis; FSSA
analysis designed to evaluate the potential impact of a hypothetical fire in each fire area, and verify the fire protection design in ensuring the realization and maintenance of safe shutdown by process and related system
3.20
fire safety analysis
analysis designed to ensure the post-fire nuclear safety function and verify the adequacy of fire protection design, including FHA, FVA and FSSA
3.21
solid separation
separation of items by fire barriers with a certain fire resistance rating to avoid the spread of fire
3.22
geographical separation
separation of items by distance with no combustible materials arranged in the separated space to avoid the spread of fire
4 General requirements for fire protection design
4.1 General
4.1.1 The fire protection design of nuclear power plants shall fully implement the policy of "prevention first and combination of fire prevention and firefighting". The fire protection design of nuclear safety important building and structure shall abide by the principle of "defense in depth" to achieve the following objectives:
——prevent fire;
——quickly detect and extinguish any fire that has actually occurred, thus limiting the damage caused by the fire;
——prevent the spread of fire which has not been extinguished, so as to minimize its impact on systems necessary to perform important safety functions.
4.1.2 The buildings, structures, systems and components of a nuclear power plant shall be designed and arranged so as to minimize the possibility of a fire initiated by internal or external event and to mitigate its consequences.
4.2 Basic purpose
4.2.1 The following nuclear safety functions shall be ensured during and after a fire:
——control of reactivity;
——discharge of waste heat from reactor core and release of heat from the fuel stored in the spent fuel storage facility;
——planned emission for permitting radioactive materials, shielding radiation and controlling radioactivity, and limit of radioactive release in case of an accident.
4.2.2 The capability to monitor the state of the nuclear power plant shall be ensured during and after a fire to guarantee the realization of required safety functions.
4.2.3 Restrict and extinguish, as promptly as practicable, any fire that could lead to prolonged unavailability of the nuclear power plant.
4.2.4 Ensure the personal safety of the working personnel by taking measures for their safe evacuation in the event of a fire and by establishing conditions to enable firefighting and rescue operations.
4.3 Basic assumptions
4.3.1 Fires shall be considered to occur under normal operating conditions of the unit (from full power to shutdown state).
4.3.2 Fires may occur in any location containing fixed or temporary combustible materials.
4.3.3 The simultaneous occurrence of two or more independent fire events within the same unit plant building or different unit plant buildings shall not be considered.
4.3.4 The simultaneous occurrence of a fire and an independent nuclear safety accident (event), failure of nuclear safety-related equipment or other hazard shall not be considered, unless a causal relationship exists between the fire and the above accident.
4.3.5 In the fire safety analysis, for anticipated operation events and design basis accidents, the possibility of an independent fire occurring after the unit has reached a safe shutdown state shall be considered.
4.3.6 In the fire safety analysis, given the complexity of the nuclear power plant conditions following extended design conditions or an earthquake, only the possibility of an independent fire in the long-term stage under the extended design conditions or after an earthquake shall be considered. The specific duration of the long-term stage shall be determined based on a conservative assumption of the time required to fully mitigate the extended design conditions or earthquake and for the unit to reach a final safe state, which should be 15 days.
4.4 Prevention of common mode failure in nuclear safety important building and structure
Contents
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General requirements for fire protection design
5 Fire protection design for general layout
6 Fire prevention and fire spread restriction
7 Fire evacuation
8 Automatic fire alarm system
9 Fire water supply and fire extinguishing system
10 Ventilation, fire protection, smoke prevention and exhaust
11 Fire safety analysis
12 Internal explosion protection design
13 Fire protection design requirements for key areas and equipment
14 Quality assurance
Annex A (Normative) Seismic requirements
Annex B (Normative) Commissioning and periodic test
Annex C (Informative) Fire-resistant wrapping requirements for cable tray section
Annex D (Informative) Type of fire hazards
