An evaluation method for the safe shutdown path of a nuclear power plant fire accident

Abstract

The present invention discloses a method for evaluating the safety shutdown path in a nuclear power plant fire accident, comprising the following steps: identifying the systems that affect the functions for safety shutdown and establishing the safety shutdown path; identifying the equipment that executes or is affected according to the functions for safety shutdown; identifying and determining the cables of the equipment that affect safety shutdown; and performing circuit analysis and evaluation on the cables involved in safety shutdown within the fire compartment. The method for evaluating the safety shutdown path in a nuclear power plant fire accident of the present invention, by identifying the systems, equipment and cables required for the operation of each safety shutdown path in the nuclear power plant and considering the malfunction of the cables in case of fire, provides measures for the nuclear power plant to mitigate the impact of fire on the components of each safety shutdown path required for each fire compartment or the components that may affect the required safety shutdown path, so as to enable the nuclear power plant to reach an acceptable safety level and achieve the safety design of the nuclear power plant.

Description

[0001] This application is a divisional application of the invention patent application with the application date of October 26, 2020, application number 2020111536465, and invention title "Evaluation Method for Safe Shutdown Path of Nuclear Power Plant Fire Accident". Technical Field

[0002] The present invention belongs to the field of nuclear safety technology, and particularly relates to an evaluation method for safe shutdown path of nuclear power plant fire accident. Background Art

[0003] The operating experience of nuclear power plants over the past few decades has shown that fire poses a significant potential threat to the safety of nuclear power plants. Fires in nuclear power plants can directly penetrate the layers of barriers set in the deterministic accident analysis of nuclear power plants, trigger reactivity accidents, and also cause serious economic losses and social impacts.

[0004] In order to prevent the occurrence of fire accidents and extinguish fires in a timely manner when a fire occurs, nuclear power plants have carried out systematic analysis and research on the impact of fire accidents on the safe shutdown of reactors during the design and operation processes.

[0005] As is well known, a nuclear power plant is an extremely complex system, and the operation process of the reactor relies on hundreds of systems and related equipment in the nuclear power plant. When a fire accident occurs, the unit needs to shut down to ensure the safety of the unit. The main safety functions required for the safe shutdown of the unit in case of fire include: reactivity control, primary loop pressure control, primary loop water inventory control, core heat removal, process parameter monitoring, and other related support systems. These functions have a direct impact on achieving and maintaining the hot shutdown of the unit, thereby ensuring the integrity of the fuel, pressure vessel, and containment. Therefore, once the systems and equipment required for the hot shutdown of the unit are damaged due to fire, it will seriously affect the shutdown of the unit and thus seriously affect nuclear safety.

[0006] A nuclear power plant needs to ensure a necessary safe shutdown path to achieve and maintain the hot shutdown of the unit, which will not be damaged due to fire, thereby ensuring the safety of the nuclear power plant under fire accident conditions. Summary of the Invention

[0007] In view of this, in order to overcome the defects of the prior art, the purpose of the present invention is to provide an evaluation method for safe shutdown path of nuclear power plant fire accident (SSA), which can be used to identify and evaluate the capabilities of structures, systems, and components (SSCs) necessary to achieve and maintain safe shutdown conditions in case of fire.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] An evaluation method for the safety shutdown path of a nuclear power plant fire accident includes the following steps: identifying the systems that affect the functions of safety shutdown, and establishing a safety shutdown path; identifying the equipment that executes or affects according to the functions of safety shutdown; identifying and determining the cables of the equipment that affect safety shutdown; and performing circuit analysis and evaluation on the cables related to safety shutdown within the fire compartment.

[0010] According to some preferred implementation aspects of the present invention, the functions of safety shutdown include reactivity control, primary loop pressure control, water inventory control, core residual heat removal, process monitoring, and power, cooling, and ventilation support systems.

[0011] According to some preferred implementation aspects of the present invention, establishing a safety shutdown path includes the following steps: identifying each system that meets the functions of safety shutdown; determining the important systems that implement each safety shutdown function, and setting this group of important systems as a safety shutdown path.

[0012] According to some preferred implementation aspects of the present invention, the step of identifying the equipment that executes or affects safety shutdown according to the safety shutdown path includes the following steps: identifying the system flow path for each safety shutdown path; identifying the equipment that meets the functions of safety shutdown according to the system flow path; determining whether there is equipment belonging to other systems;

[0013] If not, then count the safety shutdown equipment list and correspond it to the system and the safety shutdown path one by one; identify the equipment information related to safety shutdown; identify the correlation between the equipment, associated equipment, system, and path, and establish a logical block diagram of the equipment, system, and path;

[0014] If so, then allocate the determined support system to the system combination of the corresponding shutdown path.

[0015] According to some preferred implementation aspects of the present invention, the identification of the equipment is carried out by referring to the process and instrumentation diagrams, electrical diagrams, and flow charts of the system; the identification of the equipment information is carried out by referring to the system equipment manual and fire compartment report materials.

[0016] According to some preferred implementation aspects of the present invention, the equipment information includes equipment type, equipment description, fire compartment, room number, and the normal position and failure position of the equipment.

[0017] According to some preferred implementation aspects of the present invention, the cables of the equipment that affect safe shutdown are identified and determined, including the following steps: identifying the circuits required for the operation of each safe shutdown equipment; identifying the equipment whose malfunction or incorrect operation will affect safe shutdown; identifying the interlock circuits and cables whose failure will cause incorrect startup; determining whether the operation of the equipment requires power; if power is required, identifying the nearest upstream power supply and verifying that the upstream power supply is on the safe shutdown list, and then allocating the cable to the equipment; if power is not required, directly allocating the cable to the equipment; determining the routing of the cable; and confirming the location of the cable according to the fire compartment.

[0018] According to some preferred implementation aspects of the present invention, during the process of identifying the circuit, it is necessary to consult the electrical single-line diagram, electrical schematic diagram, basic wiring diagram, and terminal connection diagram corresponding to the equipment to determine the cables that need to be kept intact or the cables that may cause improper operation of each safe shutdown equipment.

[0019] According to some preferred implementation aspects of the present invention, circuit analysis and evaluation are carried out on the cables related to safe shutdown in the fire compartment, including the following steps: identifying and locating the cables for safe shutdown according to the fire compartment; confirming the affected cables and equipment in the fire compartment; determining the minimum safe shutdown path affected in the fire compartment and designating it as the path required for safe shutdown; confirming the impact of the equipment on the circuits required for safe shutdown; and formulating mitigation strategies or measures to protect the cables and equipment affected by the fire.

[0020] According to some preferred implementation aspects of the present invention, the mitigation strategies or measures include: fireproof wrapping of the relevant cables; adding fire barriers with corresponding fire resistance levels; adding fire-resistant barriers with automatic fire extinguishing and detection devices; and identifying other equipment that performs the same safe shutdown function.

[0021] Due to the adoption of the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows: The method for evaluating the safe shutdown path in the nuclear power plant fire accident of the present invention, by identifying the systems, equipment, and cables required for the operation of each safe shutdown path in the nuclear power plant and considering the malfunction of the cables in the event of a fire, provides measures for the nuclear power plant to mitigate the impact of the fire on the components of each fire compartment required for the safe shutdown path or the components that may affect the required safe shutdown path, so as to enable the nuclear power plant to reach an acceptable safety level and achieve the safe design of the nuclear power plant. Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is an analysis strategy diagram of the evaluation method for the safe shutdown path of the nuclear power plant fire accident in the preferred embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the establishment of the safe shutdown path of the nuclear power plant fire accident in the preferred embodiment of the present invention;

[0025] Figure 3 It is a flow chart for identifying important components and equipment for safe shutdown in the preferred embodiment of the present invention;

[0026] Figure 4 It is a flow chart for identifying and determining relevant cables of equipment affecting safe shutdown in the preferred embodiment of the present invention;

[0027] Figure 5 It is a flow chart for the analysis and evaluation of fire compartments in the preferred embodiment of the present invention. Detailed implementation manners

[0028] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] There are hundreds of systems in a nuclear power plant, and these systems perform different functions. Only a part of them perform the function of safe shutdown (SSD). At the same time, the safety systems of nuclear power plants are mostly redundantly configured. Therefore, under the condition of a nuclear power plant fire accident, only the availability of some systems and equipment needs to be ensured to ensure that the nuclear power plant can reach a safe shutdown state.

[0030] Basic assumptions for the analysis of nuclear power plant fire safety shutdown: A single fire occurs in the area (or with fire hazards) containing the SSCs required for safe shutdown; Except for certain exceptions, all exposed cables and equipment are assumed to be damaged by fire; All equipment is in its normal position before the fire occurs; The unit is operating at full power.

[0031] The purpose of this embodiment is to provide an evaluation method for the above-mentioned nuclear power plant fire safety shutdown analysis (SSA), as Figure 1As shown in the figure, the evaluation method for safe shutdown includes the following steps: starting from the safe shutdown function of the nuclear power plant, identifying the safe shutdown system, and then confirming and identifying the equipment and cables in the safe shutdown path through flowcharts and other drawings. Then, identify the important cables and equipment for safe shutdown in each fire compartment involved in the safe shutdown path through circuit analysis methods. Finally, select appropriate mitigation and protection measures to protect the cables and ensure the integrity of the safe shutdown path in case of a fire, thereby ensuring the safety of the nuclear power unit.

[0032] The fire and safe shutdown evaluation method is a method for identifying and evaluating the ability of structures, systems, and components (SSCs) necessary to achieve and maintain safe shutdown conditions in case of a fire, specifically including the following 4 steps:

[0033] 1. Identify the important systems required for hot shutdown or affecting the safe shutdown (SSD) function

[0034] The goal of safe shutdown after a fire is to ensure that the safe shutdown path composed of shutdown systems, structures, and components required for a hot shutdown in one column is protected from fire damage. Achieving this goal requires determining the functions necessary to achieve and maintain hot shutdown.

[0035] The functions required for safe shutdown after a fire include the following aspects: reactivity control, primary circuit pressure control, water inventory control, core residual heat removal, process monitoring, and support systems such as power, cooling, and ventilation. These functions have a direct impact on achieving and maintaining the goal of safe shutdown for hot shutdown, thereby ensuring the integrity of the fuel, pressure vessel, and containment.

[0036] Under different operating conditions, the systems that perform corresponding safety functions are not fixed. As Figure 2 shown, first identify each system that meets the safe shutdown function; then determine the important systems for each safe shutdown function to achieve this function, and set this group of important systems as a safe shutdown path.

[0037] 2. Identify the components and equipment that execute or affect safe shutdown according to the safe shutdown path

[0038] See Figure 3 shown for the specific process of identifying the important components and equipment for safe shutdown.

[0039] First, it is necessary to identify the system flow paths in the system flowcharts for each safe shutdown path, determine which equipment should be included in the safe shutdown equipment list according to the system flow paths, and at the same time consider any equipment that may malfunction and have an adverse impact on the required system functions. As Figure 3 shown, it specifically includes the following steps:

[0040] 2.1) Identify the system flow paths for each safe shutdown path;

[0041] 2.2) Identify the equipment that meets the safe shutdown function according to the system flow path;

[0042] 2.3) Determine whether there is any equipment belonging to other systems;

[0043] 2.4) If not, count the list of safe shutdown equipment and correspond it one by one with the system and the safe shutdown path;

[0044] If so, assign the determined support system to the system combination of the corresponding shutdown path;

[0045] 2.5) Identify the equipment information related to safe shutdown;

[0046] 2.6) Identify the correlation between equipment, associated equipment, systems and paths, and establish a logical block diagram of equipment, systems and paths.

[0047] Identify the important equipment for safe shutdown by referring to drawings such as the P&ID (Process and Instrumentation) diagram, electrical diagram, flow chart, etc. of the system. Subsequently, refer to materials such as the system equipment manual (SDM), fire compartment report, etc. to confirm the equipment information required for safe shutdown analysis, including equipment type, equipment description, fire compartment, room number, and the normal position, failure position, etc. of the equipment.

[0048] Determine the important equipment and its related information required for implementing the safe shutdown path through this step.

[0049] 3. Identify and determine the relevant cables of the equipment that affect safe shutdown

[0050] See Figure 4 As shown, for each piece of equipment identified in the previous step, refer to the circuits required for the operation of the equipment, including power supply, control or instrumentation circuits, etc. At the same time, it is necessary to delete the cables of the circuits that have no effect on the safe shutdown function of the equipment (such as annunciator circuits, heating circuits, etc.), unless these circuits are relied upon. During the circuit identification process, it is necessary to focus on identifying the interlock circuits and cables whose malfunction or improper operation may affect shutdown. Refer to drawings such as the electrical single-line diagram, electrical schematic diagram, basic wiring diagram, terminal connection diagram, etc. corresponding to the equipment to determine the cables that need to be kept intact or the cables that may cause improper operation of each safe shutdown equipment. As Figure 4 shown, the specific steps are as follows:

[0051] 3.1) Identify the circuits required for the operation of each safe shutdown equipment;

[0052] 3.2) Identify the equipment whose malfunction or improper operation will affect safe shutdown;

[0053] 3.3) Identify the interlock circuits and cables whose failure will cause mis-starting;

[0054] 3.4) Determine whether the operation of the equipment requires power supply;

[0055] If power supply is required, identify the nearest upstream power supply and verify that the upstream power supply is on the safe shutdown list, then proceed to step 3.5); if power supply is not required, directly proceed to step 3.5);

[0056] 3.5) Allocate cables to the equipment

[0057] 3.6) Determine the cable routing;

[0058] 3.7) Confirm the cable location according to the fire compartment.

[0059] Search for the cable information corresponding to the number through the cable inventory, including the starting position of the cable, the rooms and fire compartments passed through, and locate the cable.

[0060] 4. Conduct circuit analysis and evaluation on the cables related to safe shutdown in the fire compartment

[0061] Including the following steps: identify and locate the cables for safe shutdown according to the fire compartment; confirm the affected cables and equipment in the fire compartment; determine the minimum safe shutdown path affected in the fire compartment and designate it as the path required for safe shutdown; confirm the impact of the equipment on the circuit required for safe shutdown; formulate mitigation strategies or measures to protect the cables and equipment affected by the fire.

[0062] Specifically, as Figure 5 shown, according to the review of the systems, equipment and cables in each fire compartment, determine the shutdown path in this compartment that is not affected by or least affected by the hypothetical fire. Select the safe shutdown path with the fewest cables and equipment in this compartment as the path required for safe shutdown.

[0063] Conduct circuit failure analysis on the equipment along the determined safe shutdown path, consider the impact of circuit faults such as thermal short circuit, short circuit, grounding, etc. on the cables and equipment, and determine the cables and equipment that will be damaged by the fire in each fire compartment according to the results of the circuit failure analysis.

[0064] For the cables and equipment that will be damaged by the fire in each fire compartment, select appropriate measures to mitigate or eliminate the fire damage. These strategies and measures may include: fireproof wrapping of the relevant cables; adding fire barriers with corresponding fire resistance levels; adding fire-resistant barriers with automatic fire extinguishing and detection devices; identifying other equipment that performs the same safe shutdown function, etc.

[0065] Through the above steps and methods in this embodiment, the evaluation method of the safe shutdown path for nuclear power plant fire accidents in this embodiment identifies the systems, equipment, and cables required for the operation of each safe shutdown path in the nuclear power plant, and considers the malfunction situation of the cables in case of fire, providing measures for the nuclear power plant to mitigate the impact of fire on the components of each safe shutdown path required for each fire compartment or the components that may affect the required safe shutdown path, so as to enable the nuclear power plant to reach an acceptable safety level and achieve the safety design of the nuclear power plant.

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. An evaluation method for the safe shutdown path of a nuclear power plant fire accident, characterized in that The goal of the safe reactor shutdown in case of a fire accident is to ensure that the safe reactor shutdown path composed of the shutdown systems, structures, and components required for one train to reach hot shutdown is not damaged by the fire; the basic assumptions of the evaluation method for the fire safety shutdown path of a nuclear power plant are as follows: a single fire occurs in the area containing the structures, systems, and components required for safe reactor shutdown; all equipment is in its normal position before the fire occurs; the unit is operating at full power; The evaluation method includes the following steps: 1) Starting from the safe reactor shutdown function of the nuclear power plant, identify the systems that affect the safe reactor shutdown function and establish a safe reactor shutdown path; 2) Identify the equipment that executes or affects safe reactor shutdown according to the safe reactor shutdown path; 3) Identify and determine the cables of the equipment that affect safe reactor shutdown; 4) Conduct a circuit analysis and evaluation of the cables related to safe reactor shutdown in the fire compartment, formulate mitigation strategies or measures to ensure the integrity of the safe reactor shutdown path in case of a fire, and thus ensure the safety of the nuclear power unit; Establishing the safe reactor shutdown path in step 1) includes: first, identifying each system that meets the safe reactor shutdown function; then, determining the important systems that implement this function for each safe reactor shutdown function, and setting this group of important systems as a safe reactor shutdown path; Identifying the equipment that executes or affects safe reactor shutdown in step 2) includes: identifying the system flow paths in the system flow diagram for each safe reactor shutdown path, determining which equipment should be included in the safe reactor shutdown equipment list according to the system flow paths, and also considering all equipment whose malfunction has an adverse impact on the required system function; Identifying and determining the cables of the equipment that affect safe reactor shutdown in step 3) includes: for each piece of equipment identified in step 2), consult the required circuits for the operation of the equipment, including power supply, control, or instrumentation circuits, and at the same time, it is necessary to delete the cables of the circuits that have no effect on the safe reactor shutdown function of the equipment, unless these circuits are relied upon; during the circuit identification process, it is necessary to identify the interlock circuits and cables whose malfunction or misoperation affects reactor shutdown; Conducting a circuit analysis and evaluation of the cables related to safe reactor shutdown in the fire compartment in step 4) includes the following steps: identify and locate the cables for safe reactor shutdown according to the fire compartment; confirm the cables and equipment affected in the fire compartment; determine the minimum safe reactor shutdown path affected in the fire compartment and designate it as the path required for safe reactor shutdown; confirm the impact of the equipment on the circuits required for safe reactor shutdown; formulate mitigation strategies or measures to protect the cables and equipment affected by the fire.

2. The evaluation method according to claim 1, wherein The safe reactor shutdown function includes reactivity control, primary circuit pressure control, water inventory control, core residual heat removal, process monitoring, and power, cooling, and ventilation support systems.

3. The evaluation method according to claim 1, wherein Step 2) specifically includes the following steps: 2.1) Identify the system flow paths for each safe reactor shutdown path; 2.2) Identify the equipment that meets the safe reactor shutdown function according to the system flow paths; 2.3) Determine whether there is any equipment belonging to other systems; 2.4) If not, count the safe reactor shutdown equipment list and correspond it one by one with the systems and the safe reactor shutdown paths; If so, assign the determined support system to the system combination of the corresponding shutdown path; 2.5) Identify the equipment information related to safe reactor shutdown; 2.6) Identify the correlations among the identification devices, associated devices, systems, and paths, and establish a logical block diagram of the devices, systems, and paths.

4. The evaluation method according to claim 3, characterized in that The identification of the devices is carried out by referring to the process and instrumentation diagrams, electrical diagrams, and flowcharts of the system; the identification of the device information is carried out by referring to the system device manuals and fire compartment report materials.

5. The evaluation method according to claim 4, characterized in that The device information includes device type, device description, fire compartment, room number, and the normal and failure positions of the device.

6. The evaluation method according to claim 1, characterized in that Step 3) includes the following steps: 3.1) Identify the circuits required for the operation of each safe shutdown device. 3.2) Identify the devices whose malfunction or incorrect operation will affect safe shutdown. 3.3) Identify the interlock circuits and cables whose failure will cause mis-startup. 3.4) Determine whether the operation of the device requires power. If power is required, identify the nearest upstream power source and verify that the upstream power source is on the safe shutdown list, and proceed to step 3.5); if power is not required, directly proceed to step 3.5). 3.5) Assign cables to the devices 3.6) Determine the cable routing. 3.7) Confirm the cable positions.

7. The evaluation method according to claim 6, wherein In step 3.7), the confirmation of the cable positions is as follows: Search for the cable information corresponding to the number through the cable inventory, including the starting position of the cable, the rooms and fire compartments passed through, and position the cable.

8. The evaluation method according to claim 6, wherein During the process of identifying the circuits, it is necessary to refer to the corresponding electrical single-line diagrams, electrical schematic diagrams, basic wiring diagrams, and terminal connection diagrams of the devices to determine the cables that need to be kept intact or the cables that will cause improper operation of each safe shutdown device.

9. The evaluation method according to claim 1, characterized in that Confirming the cables and devices affected in the fire compartment includes: Conducting a circuit failure analysis for the devices on the determined safe shutdown path, considering the effects of thermal short circuits, short circuits, and ground circuit faults on the cables and devices, and determining the cables and devices that will be damaged by the fire in each fire compartment based on the results of the circuit failure analysis.

10. The evaluation method according to claim 1, characterized in that, The paths required for safe shutdown are as follows: Based on the review of the systems, devices, and cables in each fire compartment, determine the shutdown paths in the compartment that are immune to or least affected by the hypothetical fire; Select the safe shutdown path with the fewest number of cables and devices in the compartment as the path required for safe shutdown.

11. The evaluation method according to claim 1, wherein The mitigation strategies or measures include: Fireproof wrapping of the relevant cables; Adding fire barriers with corresponding fire resistance ratings; Adding fire-resistant barriers with automatic fire extinguishing and detection devices; Identifying other devices that perform the same safe shutdown function.

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