A fast reactor nuclear power plant accident handling system and its design method

Abstract

The present invention relates to a fast reactor nuclear power plant accident handling system and a design method thereof, comprising: (1) determining an accident handling framework combining an event-oriented handling method with a symptom-oriented handling method according to fast reactor design feature analysis and accident characteristic analysis results; (2) designing an event-oriented accident handling system, including determining an accident condition list, an accident diagnosis strategy and an accident handling strategy; (3) designing a symptom-oriented accident monitoring system, including determining monitoring functions, monitoring symptoms and monitoring strategies; (4) executing an event-oriented accident handling system and a symptom-oriented accident monitoring system in parallel, performing accident diagnosis and response through the accident handling system, and performing correction and supplementary operations through the accident monitoring system, thereby ensuring that the accident is effectively mitigated. The design process of the present invention is complete and clear, and the feasibility is high, and the optimization of the accident handling of fast reactor nuclear power plants is achieved.

Description

Technical Field

[0001] The invention belongs to nuclear power plant design technology, and in particular relates to a fast reactor nuclear power plant accident processing system and a design method thereof. Background Art

[0002] Safety is the lifeline of nuclear power plants. The most basic safety principle of nuclear power plants is defense in depth. The integrity of several barriers that are interdependent in depth is protected by multiple safety facilities and handling procedures. According to the requirements of defense in depth, when an expected operating event or a hypothetical initiating event occurs, the operator should immediately adopt appropriate accident handling measures to mitigate the extent and impact of the accident, restore the power plant to a controlled and cooled state, and limit the release of radioactivity to ensure the safety of the power plant. It can be seen that accident handling is an important part of the defense in depth of nuclear power plants. At the same time, nuclear power plant accident handling is the most important and most complex operating task in nuclear power plants. It involves a large number of systems and equipment, requires rapid response from operators, and has complex and precise requirements for the operating strategies of each part. Therefore, accident handling technology is one of the important technologies to ensure the safety of nuclear power plants and constitute the advanced nature of nuclear power plants.

[0003] As the preferred reactor type for the fourth generation nuclear energy system, fast reactor nuclear power plants have higher requirements for safety goals. The significant design features of fast reactors include: 1) Fast reactors have inherent safety, that is, for a series of possible accidents, the reactor design can achieve a safe state by its own physical characteristics; 2) Fast reactors have passive safety facilities, which do not rely on external conditions under accident conditions, and only rely on passive equipment to prevent further development of accidents or mitigate the consequences of accidents; 3) For sodium-cooled fast reactors, liquid sodium as a coolant has active chemical properties. Once sodium leaks, it is easy to react chemically with air and water, causing sodium fire accidents and sodium water accidents. Sodium fire and sodium water are accident conditions unique to sodium-cooled fast reactor nuclear power plants, especially primary circuit sodium fires, which can also cause radioactive releases. Targeted measures need to be taken to deal with accidents; 4) Fast reactors use once-through steam generators, whose heat capacity and thermal inertia are much smaller than those of U-tube steam generators used in large pressurized water reactors, so the dynamic response is relatively rapid. Therefore, in order to ensure the safety of fast reactor nuclear power plants, it is necessary to establish and maintain a reliable and effective accident handling system based on the design characteristics and unique accident phenomena of fast reactors.

[0004] At present, my country's fast reactor nuclear power plant operation experience is insufficient. The China Experimental Fast Reactor has only a few years of operation experience. Its operation documents for accident handling are not perfect, and a complete accident handling system has not been formed. The international fast reactor operation experience is also relatively lacking. Due to political, economic and other factors, many reactors are experimental-prototype reactors and have been shut down for a long time. Even the remaining fast reactor power plants are difficult to collect or reference due to differences in technical routes. On the other hand, the design principles and design concepts of pressurized water reactor nuclear power plants and fast reactor power plants are quite different, and the accident handling related development results of pressurized water reactor nuclear power plants cannot be applied to fast reactor power plants. Therefore, both domestically and internationally, fast reactor nuclear power plants have a relatively scarce experience in accident handling, and their technical accumulation is relatively weak. A complete set of accident handling methods and systems suitable for fast reactors has not yet been formed. Summary of the invention

[0005] The purpose of the present invention is to meet the safety target requirements of fast reactor nuclear power plants, determine the applicable accident handling technical direction, provide a nuclear power plant accident handling system and its design method that combines event orientation and symptom orientation, provide technical guidance for operating personnel to handle accident conditions, so as to respond to and alleviate the consequences of accidents, ensure that personnel, society and the environment are protected from radioactive hazards, and achieve the overall goal of nuclear power plant safety.

[0006] The technical solution of the present invention is as follows: a fast reactor nuclear power plant accident handling system, including an event-oriented accident handling system and a symptom-oriented accident supervision system. Accident handling of the fast reactor nuclear power plant is carried out through the event-oriented accident handling system, and accident handling is supervised through the symptom-oriented accident handling system.

[0007] Furthermore, in the fast reactor nuclear power plant accident handling system as described above, the event-oriented accident handling system includes an accident condition list, an accident diagnosis strategy system and an accident handling strategy system; the accident condition list is determined in combination with the initiating event list and the accident coverage; the accident diagnosis strategy system includes specific accident diagnosis criteria and an overall accident diagnosis system; the accident handling strategy system includes: an immediate operation strategy that the operator needs to execute immediately when an accident occurs in the nuclear power plant, a stable operation strategy that brings the nuclear power plant into a normal, stable condition or a safe steady-state condition under accident conditions to keep the nuclear power plant in a safe state, and a regular monitoring strategy for regularly checking important parameters and equipment operating status.

[0008] Furthermore, in the fast reactor nuclear power plant accident handling system as described above, the symptom-oriented accident handling system includes a supervision function system, a supervision symptom system and a supervision strategy system; the supervision function system includes supervision of key safety functions of the fast reactor nuclear power plant, supervision of power plant support functions, and supervision of power plant dedicated safety functions; the supervision symptom system determines the supervision symptoms of all functions through symptom parameter selection and symptom anomaly analysis; and the supervision strategy system includes determining the supervision order and supervision method.

[0009] The supervision method includes: entry criteria, when any accident diagnosis criterion is met, the supervision system needs to be applied to perform accident supervision; execution criteria, each function is supervised one by one in a single thread according to the supervision order, the degree of function degradation is evaluated through the abnormal situation of the function symptom parameters, and the execution is cyclical; exit criteria, when the accident condition further deteriorates to the core melting and the power plant reaches a serious accident state, or when the event-oriented accident processing has been completed and the power plant is in a safe state, the supervision is exited.

[0010] The present invention further provides a design method for the above-mentioned fast reactor nuclear power plant accident handling system, comprising:

[0011] (1) Based on the results of the fast reactor design feature analysis and accident characteristic analysis, determine to handle fast reactor nuclear power plant accidents through an event-oriented approach, and supervise the accident handling through a symptom-oriented approach;

[0012] (2) Design an event-oriented accident handling system, including determining the accident condition list, accident diagnosis strategy, and accident handling strategy;

[0013] (3) Designing a symptom-based accident monitoring system, including determining monitoring functions, monitoring symptoms, and monitoring strategies;

[0014] (4) The event-oriented accident handling system and the symptom-oriented accident monitoring system are executed in parallel. Accident diagnosis and response are carried out through the accident handling system, and correction and supplementary operations are carried out through the accident monitoring system, thereby ensuring that accidents are effectively mitigated.

[0015] Furthermore, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (2), the design of the accident condition list includes:

[0016] (2-1-1) Determine the list of initiating events of fast reactor nuclear power plants based on the accident analysis results, probabilistic safety analysis (PSA) results and the design characteristics of fast reactor nuclear power plants, including: events included in the accident analysis, key personnel actions and risk-critical tasks determined in the probabilistic safety analysis, and specific events that reflect typical design characteristics of fast reactors;

[0017] (2-1-2) Based on the classification of operating conditions and accident handling requirements of fast reactor nuclear power plants, determine the scope of accident handling for fast reactor nuclear power plants, including: accident conditions from automatic emergency shutdown to core melt, accident conditions of manual emergency shutdown, accident conditions leading to radioactive release, and accident conditions of abnormal fuel operation;

[0018] (2-1-3) A consequence analysis is conducted for each initiating event. If the accident consequence meets one or more of the covered conditions, the initiating event is determined to be an accident condition that needs to be handled, thus forming a complete list of accident conditions.

[0019] Furthermore, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (2), the design of the accident diagnosis strategy includes:

[0020] (2-2-1) Analyze the evolution process and consequences of the accident for specific accident sequences, and compile the degree of degradation of the safety functions of nuclear power plants and the changing trends of the main characteristic parameters at the early stage of the accident;

[0021] (2-2-2) Based on the analysis results of the accident evolution process and in combination with the design of the fast reactor nuclear power plant (such as operating conditions, alarms, etc.), the accident diagnosis criteria under specific accident conditions are sorted out and evaluated and analyzed to ensure that the diagnosis criteria are reliable, complete and easy to identify;

[0022] (2-2-3) By combining the design of fast reactor nuclear power plants with the characteristics and criteria of various specific accidents, and analyzing the independence and degradation degree of accident conditions, an appropriate diagnostic priority order is determined to form an overall accident diagnosis system, and a single-threaded sequential execution method is used to diagnose all conditions in the accident condition list; the diagnostic order is as follows:

[0023] a) Power loss accidents take precedence over other types of accidents;

[0024] b) Accidents with high severity take precedence over accidents with low severity;

[0025] c) High independence of diagnostic criteria takes precedence over low independence of diagnostic criteria.

[0026] Further, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (2), the design of the accident handling strategy includes:

[0027] (2-3-1) Conduct extended accident analysis and system analysis and calculations,

[0028] The extended accident analysis adopts an extended accident analysis based on the best estimation method based on realistic assumptions, and on this basis analyzes the weaknesses of the accident condition response;

[0029] The system analysis and calculations include design capacity and limit analysis of safety-related systems and equipment, consequence analysis of safety-related systems, and performance analysis of required support systems, in order to evaluate the availability and reliability of measures adopted after an accident;

[0030] (2-3-2) Develop a strategic framework, including two stages: stabilizing the unit status and retreating to a safe shutdown state:

[0031] Stabilize the unit status Based on the analysis results of step (2-3-1), combined with the safety functions and system design of the fast reactor nuclear power plant, determine the control and mitigation methods of each safety function of the fast reactor nuclear power plant to achieve stable unit status;

[0032] Retreat to safe shutdown state The safe retreat state of the unit is determined according to the system configuration state and the requirements for safety functions under specific accident conditions;

[0033] (2-3-3) Further clarify the policy details through compliance calculation;

[0034] (2-3-4) Ensure the correctness, availability and integrity of the accident handling strategy through strategy confirmation.

[0035] Furthermore, in the design method of the accident handling system of the fast reactor nuclear power plant as described above, in step (2), the accident handling strategies determined include: an immediate operation strategy that the operator needs to execute immediately when an accident occurs in the nuclear power plant; a stable operation strategy that brings the nuclear power plant to a normal, stable operating condition or a safe steady-state condition under accident conditions so that the nuclear power plant is in a safe state; and a regular monitoring strategy that regularly checks important parameters and equipment operating status.

[0036] Furthermore, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (3), the design of the supervisory function includes:

[0037] (3-1-1) Oversee key safety functions of fast reactor nuclear power plants, including reactivity control, residual heat removal, radioactive shielding, and sodium safety;

[0038] (3-1-2) Supervise the power plant support functions, including: power supply system, gas supply system, cooling system, sodium fire / sodium water treatment system;

[0039] (3-1-3) Supervise the power plant’s dedicated safety functions, including emergency waste heat removal system and containment isolation system.

[0040] Furthermore, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (3), the design of the monitoring symptom includes:

[0041] (3-2-1) Select symptom parameters, analyze from the aspects of function analysis, probabilistic safety analysis, accident analysis, and system design, and extract symptom parameters corresponding to the functions;

[0042] (3-2-2) Perform symptom abnormality analysis on symptom parameters and select reasonable abnormal values ​​to characterize the degree of functional degradation.

[0043] Furthermore, in the above-mentioned method for designing an accident handling system for a fast reactor nuclear power plant, in step (3), the design of the supervision strategy includes:

[0044] (3-3-1) A reasonable supervision sequence is formed by determining the supervision principles, which include:

[0045] First, monitor whether a sodium fire occurs in the power plant and confirm that the sodium fire fighting operation has been performed correctly;

[0046] Confirm the reliability of the instrumentation and control power supply to ensure the authenticity of the monitoring information used;

[0047] The priority of safety functions is generally reactivity control, residual heat extraction and radioactivity shielding;

[0048] Monitoring the availability of dedicated safety facilities;

[0049] Availability monitoring of critical support systems;

[0050] (3-3-2) Determine the supervision method and determine the entry, execution and exit criteria of supervision in accordance with the requirements for the parallel execution of the event-oriented accident handling system and the symptom-oriented accident monitoring system and the accident handling coverage.

[0051] The beneficial effects of the present invention are as follows:

[0052] 1) The present invention proposes an accident handling method for a fast reactor nuclear power plant, which fully reflects the design characteristics of the fast reactor and fills the technical gap in the field of fast reactor accident handling design. The design process of the method is complete and clear, and the feasibility is high. It is suitable for fast reactor power plants. According to the design method, the accident handling design of fast reactor power plants can be effectively carried out to achieve the optimization of accident handling of fast reactor power plants.

[0053] 2) The present invention proposes a method for designing an accident handling framework for a fast reactor nuclear power plant. By conducting fast reactor design feature analysis, accident characteristic analysis and accident handling method analysis, the accident handling framework is determined and the top-level design of the accident handling system is completed.

[0054] 3) The present invention proposes a method for designing an accident condition list for a fast reactor nuclear power plant. By conducting accident analysis and probabilistic safety analysis and combining the fast reactor design characteristics, the initiating event is determined, and then the accident condition list is screened out according to the accident handling scope to ensure the integrity and inclusiveness of the accident handling scope.

[0055] 4) The present invention proposes an event-oriented accident diagnosis strategy design method for fast reactor nuclear power plants. By conducting an initial process analysis of the accident and an accident diagnosis criterion analysis, the diagnostic criteria for a specific accident are determined; and an accident diagnosis priority analysis is conducted to determine the overall accident diagnosis system, thereby ensuring the integrity, correctness and timeliness of the accident diagnosis and enabling operators to respond quickly and accurately to accidents.

[0056] 5) The present invention proposes an event-oriented accident handling strategy design method for fast reactor nuclear power plants. By carrying out support analysis, strategy framework development, compliance calculation and strategy confirmation, the handling strategy for specific accidents is determined to ensure that the accident handling strategy is reasonable, reliable and effective, effectively mitigate the consequences of the accident, and bring the power plant into a safe shutdown state.

[0057] 6) The present invention proposes a symptom-oriented accident supervision strategy design method for fast reactor nuclear power plants. By carrying out supervision function design, supervision symptom design and supervision strategy design, the required supervision functions and their supporting symptoms are determined, and a reasonable supervision sequence and supervision method are formed, thereby forming a complete and reasonable accident supervision strategy to ensure that accident supervision is both sufficiently global and sufficiently targeted, and to ensure effective supervision of power plant accident handling.

[0058] 7) The present invention proposes an event-oriented and symptom-oriented combined accident handling system for fast reactor nuclear power plants, the system includes an event-oriented accident handling system and a symptom-oriented accident monitoring system, and the accident handling system and the accident monitoring system are executed simultaneously and in parallel. The event-oriented accident handling system takes the best recovery measures for a single event to achieve rapid and accurate diagnosis and optimal recovery of the accident; the symptom-oriented accident monitoring system continuously monitors the abnormal conditions of functional symptoms, evaluates the degree of functional degradation and the effectiveness of the adopted accident strategy, and provides supplementary operations for complex working conditions and superimposed events. The event-based accident handling system and the symptom-based accident monitoring system are organically combined to construct an advanced accident handling system. The system fully reflects the design characteristics of fast reactor nuclear power plants, meets the accident handling requirements of fast reactor nuclear power plants, improves the depth defense level of fast reactor nuclear power plants, and fully reflects the safety and advancement requirements of the fourth-generation nuclear energy system. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1This is a flow chart of a design method for an accident handling system for a fast reactor nuclear power plant according to the present invention;

[0060] Figure 2 It is a schematic diagram of the fast reactor nuclear power plant accident handling system of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0062] In developing accident handling methods and systems for fast reactor nuclear power plants, full consideration must be given to the design features of fast reactors. On the one hand, full use must be made of the advantages of fast reactors, such as high inherent safety, passive safety facility design, and low-pressure main circuit, to determine an appropriate list of accident conditions and select the optimal accident handling strategy. On the other hand, for fast reactor power plants that use chemically active liquid metals as coolants (such as sodium), possible consequences of leakage must be considered, and diagnostic and handling strategies for sodium fire accidents and sodium water accidents must be developed in the accident handling design.

[0063] Based on the design characteristics of fast reactors, this invention proposes an accident handling method that combines event-oriented and symptom-oriented methods, and develops an accident handling system suitable for fast reactors on this basis to achieve the best handling of fast reactor accident conditions. The following technical problems need to be solved:

[0064] Determine the accident handling framework: To develop an accident handling system, we should first carry out top-level design and determine the overall accident handling framework. Generally, the accident handling methods of nuclear power plants are divided into event-oriented and symptom-oriented methods. The two methods have different technical characteristics and applicability. Therefore, it is necessary to determine an accident handling framework suitable for fast reactor nuclear power plants based on the design characteristics and accident characteristics of fast reactors and the technical characteristics of the above two methods.

[0065] Determine the list of accident conditions: If the coverage of accident handling is too small, the accident conditions cannot be fully covered, thus missing the response measures for some accidents; if the coverage is too large, the accident handling is not targeted, which is not conducive to the rapid diagnosis and rapid handling of accident conditions, and is not conducive to the safety of power plants. Therefore, the boundaries of accident conditions should be clarified to determine a reasonable coverage of accident handling, and on this basis, the list of accident conditions should be determined to achieve targeted, effective and rapid accident handling.

[0066] Determine the accident diagnosis strategy: In order to enable operators to respond quickly and accurately to power plant accidents, it is necessary to establish an appropriate accident diagnosis strategy. By selecting reliable, complete and easily identifiable accident signs to clarify the nature of the accident, it is helpful to guide the operator to "prescribe the right medicine" and choose the correct accident handling strategy.

[0067] Determine the accident handling strategy: Based on the accident characteristics analysis and power plant design, determine a reasonable and effective accident handling strategy, guide the operator to take appropriate accident handling measures to mitigate the consequences of the accident, ensure the safety of the core, and limit the release of radioactivity. The strategy generally includes the confirmation of the automatic response of the power plant's safety actions, the use of safe, reliable and reasonably available systems / equipment to correct / mitigate specific accident consequences, stabilize the unit status and withdraw the unit to a safe shutdown state.

[0068] Determine the accident supervision strategy: Based on the severity of the accident status and the degradation of the power plant's functional status, evaluate the applicability of the specific accident handling strategy and the safety level of the power plant, ensure that the accident handling strategy is correctly implemented, and provide appropriate supplementary operating requirements for complex operating conditions, superimposed accidents and human errors.

[0069] Nuclear power plant accident handling is the most important and also the most complex operation task in a nuclear power plant. It involves a large number of systems and equipment and requires rapid response from operators. In order to meet the safety target requirements of fast reactor nuclear power plants and the task requirements of nuclear power plant accident handling, the present invention proposes a fast reactor nuclear power plant accident handling system and its design method based on the design characteristics and accident characteristics analysis of fast reactor nuclear power plants, combined with the characteristics of event-oriented and symptom-oriented methods, such as Figure 1 As shown, the specific technical solution is as follows:

[0070] (1) Accident handling framework design

[0071] 1.1) Analysis of accident handling methods

[0072] Generally, the handling of nuclear power plant accidents is divided into event-oriented and symptom-oriented methods. The two methods have different technical characteristics and applicability: the event-oriented method takes the best recovery measures for a single specific event to mitigate the consequences of the accident, but it has problems such as insufficient ability to deal with complex and superimposed accidents and poor prevention of human errors; the symptom-oriented method evaluates the degradation level of the power plant by monitoring abnormal changes in safety-related signs of the nuclear power plant, focusing on key safety functions and providing multiple mitigation measures, but it has a lengthy document system, which is not conducive to implementation, and is not the best countermeasure under specific accidents. Therefore, it is necessary to combine the design characteristics of fast reactors and the analysis of accident characteristics to determine the appropriate accident handling method.

[0073] 1.2) Analysis of fast reactor design characteristics

[0074] Fast reactor nuclear power plants have high inherent safety and are equipped with complete safety facilities, including shutdown systems, residual heat removal systems and containment isolation systems, to ensure the safety of the three major nuclear safety functions of nuclear power plants (reactivity control, residual heat removal and radioactive shielding): the shutdown system, which combines active and passive functions, can ensure safe shutdown under accident conditions, terminate chain reactions, and maintain the power plant in a subcritical state; the residual heat removal system, which combines active and passive functions, can ensure the successful removal of residual heat under accident conditions to ensure the safety of the core. The containment isolation system ensures the integrity of radioactive shielding under extreme conditions and ensures the safety of the public and the environment. In addition, in order to cope with the potential threats posed by chemically active coolants, special facilities are configured in the design of fast reactor power plants, such as sodium fire detection and firefighting, sodium water detection and mitigation, etc.

[0075] 1.3) Analysis of fast reactor accident characteristics

[0076] Due to the unique design features of fast reactors, the process of accidents can be delayed through inherent safety and automatic response of power plants in the early stage of accidents, providing operators with a sufficient time window for accident diagnosis, making it easy to determine the type and nature of the accident and take the best recovery measures. In addition, when complex or superimposed accidents occur in fast reactors, the consequences of the accidents are generally manifested as insufficient residual heat removal capacity. The main goal of accident handling is to restore the core cooling system and ensure the residual heat removal capacity.

[0077] In summary, based on the analysis of fast reactor design characteristics and accident characteristics, the event-oriented accident handling method is conducive to the rapid diagnosis and optimal recovery of fast reactor power plant accidents. On the other hand, in order to avoid human errors such as misdiagnosis and misoperation, the symptom-oriented method can be used to continuously supervise the accident handling, comprehensively evaluate the current power plant degradation level and the effectiveness of the accident handling measures taken, and provide corrective or supplementary operational suggestions based on the symptom status of the power plant, so as to ensure that the accident is effectively mitigated.

[0078] (2) Design of event-oriented accident handling system

[0079] The accident handling system includes three parts: determining the accident condition list, determining the diagnosis strategy and determining the accident handling strategy.

[0080] 2.1) Design of accident condition list based on event orientation

[0081] 2.1.1) List of initiating events

[0082] First, the list of initiating events of fast reactor nuclear power plants is determined based on the accident analysis results, probabilistic safety analysis (PSA) results and the design characteristics of fast reactor nuclear power plants, including:

[0083] Events included in the accident analysis;

[0084] Key personnel actions and risk-significant tasks identified in the probabilistic safety analysis;

[0085] Specific events that characterize the typical design features of fast reactors.

[0086] 2.1.2) Accident handling coverage

[0087] According to the classification of operating conditions and accident handling requirements of fast reactor power plants, the scope of accident handling of fast reactor nuclear power plants is determined as follows:

[0088] - Automatic emergency shutdown to accident conditions before core melt;

[0089] -Accident conditions of manual emergency shutdown;

[0090] - accident conditions leading to radioactive releases;

[0091] -Accident conditions with abnormal fuel operation.

[0092] The above four coverages are not independent but cross-cutting, and the overlapping parts between them ensure the integrity of the coverage. It should be additionally explained that the typical accident conditions of fast reactor nuclear power plants, such as the primary circuit sodium fire accident, belong to the "accident conditions from automatic emergency shutdown to core melting" and "accident conditions leading to radioactive release", the secondary circuit sodium fire accident belongs to the "accident conditions of manual emergency shutdown", and the large sodium water accident belongs to the "accident conditions of manual emergency shutdown".

[0093] 2.1.3) Accident Condition List

[0094] After determining the list of initiating events and the accident coverage, a consequence analysis is conducted for each initiating event. If the accident consequence meets one or more items in the accident coverage, the initiating event is determined to be an accident condition that needs to be handled, thus forming a complete list of accident conditions.

[0095] 2.2) Design of accident diagnosis strategy based on event orientation

[0096] After determining the list of accident conditions, the accident diagnosis strategy design is carried out according to the fast reactor power plant design to achieve rapid identification and response to accidents. The design method is as follows:

[0097] 2.2.1) Analysis of the initial process of the accident

[0098] For a specific accident sequence, the accident evolution process and consequences are analyzed, and the degree of degradation of power plant safety functions and the changing trends of main characterization parameters at the initial stage of the accident are sorted out.

[0099] 2.2.2) Analysis of accident diagnosis criteria

[0100] Based on the results of the initial process analysis of the accident and combined with the design of the fast reactor power plant (such as operating conditions, alarms, etc.), the accident diagnosis criteria under this specific accident condition are sorted out and evaluated and analyzed to ensure that the diagnostic criteria are reliable, complete and easy to identify.

[0101] 2.2.3) Accident diagnosis priority analysis

[0102] In order to improve the accuracy, completeness and timeliness of accident diagnosis, a reasonable accident diagnosis system must be established to determine the priority of various accident diagnoses. By combining the design of fast reactor nuclear power plants with the characteristics and criteria of various specific accidents, and analyzing the independence and degradation degree of accident conditions, the appropriate diagnostic priority sequence can be determined. The following two points need to be considered:

[0103] a) To conduct reliable diagnosis, a reliable power supply is required. Therefore, compared with other types of accidents, the power supply status should be verified first.

[0104] b) Because several accidents of different types can generate the same alarm or criterion, they should be processed in order from high to low based on the severity of the accident and the independence of the criterion.

[0105] For specific accidents, through the analysis of the initial process of the accident and the analysis of the accident diagnosis criteria, reliable, measurable, easily identifiable and representative accident diagnosis criteria are selected to ensure the correctness and completeness of the specific accident diagnosis.

[0106] 2.2.4) Overall accident diagnosis system

[0107] According to the results of the accident diagnosis priority analysis, an overall accident diagnosis system is formed, a reasonable diagnosis sequence is determined, and a single-threaded sequential execution method is adopted to realize the diagnosis of all conditions in the accident condition list, ensure the integrity of the diagnosis, and improve the timeliness of the diagnosis. The diagnosis sequence is as follows:

[0108] a) Power loss accidents take precedence over other types of accidents;

[0109] b) Accidents with high severity take precedence over accidents with low severity;

[0110] c) High independence of diagnostic criteria takes precedence over low independence of diagnostic criteria.

[0111] 2.3) Design of event-oriented accident handling strategy

[0112] For specific accidents, after determining the accident diagnosis criteria, it is necessary to provide a supporting, reasonable and effective accident handling strategy.

[0113] The development of accident handling strategies based on event orientation mainly includes four stages: support analysis, strategy framework development, compliance calculation and strategy confirmation. The strategy framework is formed based on the support analysis results, the strategy framework is refined through compliance calculation, and the effectiveness and rationality of the strategy are evaluated through confirmation, thus completing the design of the accident handling strategy for fast reactor nuclear power plants.

[0114] 2.3.1) Support analysis

[0115] Support analysis is the basis for developing the accident handling system of fast reactor nuclear power plants. It mainly includes two aspects:

[0116] a) Extended accident analysis: Based on the safety analysis of fast reactor nuclear power plants and combined with engineering judgment, the extended accident analysis using the best estimation method based on realistic assumptions is determined, and on this basis, the weaknesses of the accident condition response are analyzed;

[0117] b) System analysis and calculation: including design capacity and limit analysis of safety-related systems and equipment, consequence analysis of safety-related systems, performance analysis of required support systems, etc., to evaluate the availability and reliability of measures adopted after an accident.

[0118] 2.3.2) Strategy framework development

[0119] The development of the strategy framework mainly includes two stages: stabilizing the unit status and retreating to a safe shutdown state:

[0120] a) Stabilize the unit status: Based on the support analysis results, combined with the safety functions and system design of the fast reactor nuclear power plant, determine the control and mitigation methods of each safety function of the fast reactor nuclear power plant to achieve stable unit status.

[0121] b) Withdraw to safe shutdown state: Determine the safe withdrawal state of the unit based on the system configuration status and safety function requirements under specific accident conditions.

[0122] 2.3.3) Compliance calculation

[0123] In the strategy framework development stage, the main measures and approaches adopted by the specific accident strategy have been identified, forming the main strategic points of accident handling, and the strategy details need to be further clarified through compliance calculation. Through the thermal hydraulic response analysis for specific accidents, the best estimated real model is used to determine the minimum system usage requirements, operator intervention time window, operator intervention effect, evaluate and adjust the optimization setting, etc.

[0124] 2.3.4) Strategy Confirmation

[0125] The correctness, availability and completeness of the accident handling strategy are ensured through confirmation work. On the one hand, it can be confirmed that the fast reactor accident handling strategy can completely cover all accidents in the initial event list determined at the beginning of the design, and on the other hand, it can be confirmed that the specific accident strategy can successfully handle and mitigate the corresponding accidents and bring the power plant into a safe state.

[0126] 2.4) Accident handling strategy system

[0127] The event-oriented specific accident handling strategy system includes three parts: immediate operation, stable operation and regular monitoring:

[0128] 2.4.1) Immediate Operation

[0129] When an accident occurs in a nuclear power plant, the operator must immediately implement operational strategies, including verifying whether important safety systems have been automatically activated, to prevent further deterioration of the nuclear power plant's status and mitigate the consequences of the accident.

[0130] 2.4.2) Stable operation:

[0131] It is used to bring the nuclear power plant into normal, stable or safe steady-state conditions under accident conditions, so as to keep the nuclear power plant in a safe state. It includes the stabilization and retreat stages and is the main body of the accident handling strategy.

[0132] 2.4.3) Regular monitoring:

[0133] A strategy that requires regular checks on important parameters and equipment operating status during immediate and delayed operations to allow operators to evaluate and perform relevant important operations. It includes supplementary operations and procedure conversion entries, and has the highest priority in the entire accident handling strategy.

[0134] (3) Design of accident monitoring system based on symptom guidance

[0135] The accident monitoring system includes three parts: determining monitoring functions, monitoring signs and monitoring strategies.

[0136] 3.1) Design of accident monitoring function based on symptom orientation

[0137] Focusing on the operation objectives of fast reactor power plants and based on fast reactor power plant design, power plant function analysis and task analysis are carried out to determine the power plant status functions suitable for fast reactors.

[0138] Functional analysis: Based on the safety design of fast reactor power plants, determine the functions that must be performed to meet the safety objectives of fast reactor power plants, that is, the functions that must be performed to prevent or mitigate the consequences of accidents. By decomposing the power plant safety systems and functions layer by layer, safety-related functions are refined.

[0139] Task analysis: Based on the specific strategy of the accident working condition, determine the functions required to execute the strategy. Through the gradual decomposition of the specific strategy, form the main operation tasks and sub-operation tasks, and on this basis, combine and summarize to determine the important functions.

[0140] The supervisory functions are determined as follows:

[0141] 3.1.1) Key safety functions

[0142] For fast reactor nuclear power plants, key safety functions must include not only the three major safety functions of nuclear power plants, but also the safety characteristics of liquid metal coolants. For sodium-cooled fast reactors, sodium safety must be emphasized. The details are as follows:

[0143] Reactive control;

[0144] Waste heat extraction;

[0145] Radioactive shielding;

[0146] Sodium safety.

[0147] 3.1.2) Power plant support functions

[0148] The necessary plant support systems to meet the requirements of critical safety functions require continuous monitoring of their availability. These include the following systems:

[0149] Power supply system;

[0150] Air source system;

[0151] Cold source system;

[0152] Sodium Fire / Sodium Water Treatment Systems.

[0153] 3.1.3) Power plant dedicated safety features

[0154] During the accident handling process, the availability of the power plant's dedicated safety facilities must be continuously monitored to ensure that they can be automatically or manually put into operation successfully when the accident handling is required. Including: emergency residual heat removal system, containment isolation system.

[0155] 3.2) Symptom-oriented supervision symptom design

[0156] 3.2.1) Selection of symptom parameters

[0157] In order to ensure the integrity and comprehensiveness of the required supervisory functions, the selection of function-related symptoms should ensure the comprehensiveness and diversity of the selection range, sort out and analyze from the aspects of function analysis, probabilistic safety analysis, accident analysis, and system design, and extract the symptom parameters corresponding to the function.

[0158] 3.2.2) Analysis of abnormal signs

[0159] After determining the symptom parameters corresponding to the function, an abnormal analysis of the symptom parameters should be carried out, that is, reasonable abnormal values ​​should be selected to characterize the degree of functional degradation, which is conducive to the subsequent determination of appropriate supervision strategies.

[0160] For all required supervisory functions, the supervisory symptoms of all functions are determined through symptom parameter selection and symptom anomaly analysis.

[0161] 3.3) Design of symptom-based supervision strategy

[0162] The supervision strategy includes the supervision order and supervision method. By determining the supervision principles, a reasonable supervision order is formed, and by determining the supervision method, applicable entry, execution and exit criteria are formed.

[0163] 3.3.1) Determine the supervision principles and strategies as follows:

[0164] a) First, monitor whether a sodium fire occurs in the power plant and confirm that the sodium fire fighting operation has been carried out correctly;

[0165] b) Confirm the reliability of the instrumentation and control power supply to ensure the authenticity of the monitoring information used;

[0166] c) The priority of safety functions is generally reactivity control, residual heat removal and radiation shielding;

[0167] d) Monitoring the availability of dedicated safety facilities;

[0168] e) Availability monitoring of important support systems.

[0169] Based on the above supervision principles, the supervision strategies for various supervision functions are determined as follows:

[0170]

[0171]

[0172] 3.3.2) Determine the supervision method

[0173] Based on the requirements for parallel execution of the accident handling system and the accident supervision system and the coverage of accident handling, the entry, execution and exit criteria of supervision are determined.

[0174] I) Entry criteria

[0175] When any of the accident diagnosis criteria are met, the supervision system must be used to perform accident supervision.

[0176] II) Implementation Guidelines

[0177] -Supervise each function one by one in a single thread according to the supervision order;

[0178] - Evaluate the degree of function degradation through the abnormality of the function symptom parameters; if the function is normal, continue to supervise the next function; if the function is degraded, provide corrective or supplementary operations according to the degree of degradation;

[0179] -Loop execution.

[0180] III) Exit Criteria

[0181] -When the accident condition further deteriorates to the point of core melting and the power plant reaches a severe accident state;

[0182] -When event-based accident handling has been completed and the power plant is in a safe state.

[0183] (4) The accident handling system and the accident monitoring system are executed in parallel

[0184] The accident handling system and the accident monitoring system are executed in parallel. The accident handling system is used to diagnose and respond to accidents, and the monitoring system is used to correct and supplement operations, thereby ensuring that accidents are effectively alleviated and the safety of the power plant is guaranteed. Figure 2 .

[0185] Example

[0186] (1) Accident handling framework

[0187] By conducting design feature analysis and accident characteristic analysis of sodium-cooled fast reactor nuclear power plants and combining the characteristics of event-oriented and symptom-oriented accident handling methods, the accident handling framework was determined, namely, an event-oriented accident handling system and a symptom-oriented accident supervision system.

[0188] (2) Event-oriented accident handling system

[0189] 2.1) Design of accident condition list

[0190] By combing through the accident analysis conditions and determining the key personnel actions / risk important tasks through probabilistic safety analysis, and combining the design characteristics of the sodium-cooled fast reactor, a list of initiating events is determined, and the initiating events that meet the coverage are selected as accident conditions. The list of accident conditions is shown in the following table:

[0191]

[0192] 2.2) Accident diagnosis strategy design

[0193] Taking "steam generator water loss" as an example, the design of specific accident diagnosis criteria is introduced.

[0194] First, we conducted an analysis of the initial process of the accident. When the steam generator lost all its feedwater, the feedwater flow rate dropped rapidly, resulting in a decrease in the steam generator's heat-carrying capacity and high sodium temperature at the steam generator outlet, triggering an automatic emergency shutdown and the automatic commissioning of the passive emergency heat removal system. Then, we conducted an analysis of the accident diagnosis criteria, selecting low feedwater flow as the direct diagnosis criterion and using the emergency shutdown signal as the diagnosis confirmation criterion.

[0195] In addition, the overall accident diagnosis system is the same as that described in Section 2.2.4) and will not be repeated here.

[0196] 2.3) Accident handling strategy design

[0197] Taking "steam generator feed water loss" as an example, the design of accident handling strategy is introduced.

[0198] a. Carry out support analysis, and understand the evolution of the accident and the operation of important systems through extended accident analysis based on realistic assumptions; and calculate the time for which the remaining water in the water tank can continue to supply water through system analysis.

[0199] b. Develop a strategic framework and identify key points for handling major accidents, including: confirming that the power plant has been shut down, confirming that the passive emergency heat removal system has been successfully put into operation, and isolating the steam generator.

[0200] c. Further clarify the strategy details through compliance calculations, analyze the personnel intervention time window, personnel intervention effects, evaluate and optimize constant values, etc.

[0201] d. Ensure the effectiveness of the strategy through strategy confirmation work: if the requirements are met, refine and determine the accident strategy; if the requirements are not met, return to b and re-develop the strategy framework until all accident strategies are confirmed to meet the requirements.

[0202] After the above design analysis, the strategy for the steam generator loss of feed water accident is finally formed:

[0203] -Immediate action: confirm the shutdown of the reactor and the successful commissioning of the passive emergency heat removal system;

[0204] -Stable operation: Isolate the steam generator and stabilize the unit status through the passive emergency heat removal system;

[0205] -Regular monitoring: The core outlet temperature must be monitored at all times during the accident handling process.

[0206] (3) Symptom-based accident monitoring system

[0207] Determine the functions that need to be supervised based on functional analysis and task analysis, and determine the symptom parameters and abnormal values ​​corresponding to the functions in combination with accident analysis and system design:

[0208]

[0209]

[0210] After determining the supervision functions and corresponding symptoms, the supervision strategy design is carried out, including supervision sequence, entry criteria, exit criteria and execution criteria. The supervision strategy of a pool-type sodium-cooled fast reactor nuclear power plant is the same as that described in Section 3.3.1) and will not be repeated here.

[0211] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0212] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A fast reactor nuclear power plant accident handling system, characterized in that: It includes an event-oriented accident handling system and a symptom-oriented accident monitoring system, wherein the event-oriented accident handling system is used to handle the accident of a fast reactor nuclear power plant, and the symptom-oriented accident monitoring system is used to supervise the accident handling; the event-oriented accident handling system and the symptom-oriented accident monitoring system are executed in parallel, the accident handling system is used to diagnose and respond to the accident, and the accident monitoring system is used to correct and supplement the accident, thereby ensuring that the accident is effectively mitigated; The event-oriented accident handling system includes an accident condition list, an accident diagnosis strategy system and an accident handling strategy system; The symptom-oriented accident supervision system includes a supervision function system, a supervision symptom system and a supervision strategy system; the supervision function system includes supervision of key safety functions of fast reactor nuclear power plants, supervision of power plant support functions, and supervision of power plant dedicated safety functions; the supervision symptom system determines the supervision symptoms of all functions through symptom parameter selection and symptom abnormality analysis; the supervision strategy system includes determining the supervision sequence and supervision method; The supervision method includes: entry criteria, when any accident diagnosis criterion is met, the supervision system needs to be applied to perform accident supervision; execution criteria, each function is supervised one by one in a single thread according to the supervision order, the degree of function degradation is evaluated through the abnormal situation of the function symptom parameters, and the execution is cyclical; exit criteria, when the accident condition further deteriorates to the core melting and the power plant reaches a serious accident state, or when the event-oriented accident processing has been completed and the power plant is in a safe state, the supervision is exited.

2. The fast reactor nuclear power plant accident handling system according to claim 1, characterized in that: The accident condition list is determined in combination with the initiating event list and the accident coverage; the accident diagnosis strategy system includes specific accident diagnosis criteria and an overall accident diagnosis system; The accident handling strategy system includes: an immediate operation strategy that the operator needs to execute immediately when an accident occurs in a nuclear power plant, a stable operation strategy that brings the nuclear power plant to a normal, stable operating condition or a safe steady-state condition under accident conditions to put the nuclear power plant in a safe state, and a regular monitoring strategy for regularly checking important parameters and equipment operating status.

3. A design method for an accident handling system of a fast reactor nuclear power plant, characterized in that: The steps include: (1) Based on the results of the fast reactor design feature analysis and accident characteristic analysis, determine to handle fast reactor nuclear power plant accidents through an event-oriented approach, and supervise the accident handling through a symptom-oriented approach; (2) Design an event-oriented accident handling system, including determining the accident condition list, accident diagnosis strategy, and accident handling strategy; (3) Designing a symptom-based accident monitoring system, including determining monitoring functions, monitoring symptoms, and monitoring strategies; The design of the supervision function includes: (3-1-1) Oversee key safety functions of fast reactor nuclear power plants, including reactivity control, residual heat removal, radioactive shielding, and sodium safety; (3-1-2) Supervise the power plant support functions, including: power supply system, gas supply system, cooling system, sodium fire / sodium water treatment system; (3-1-3) Supervise the power plant's dedicated safety functions, including: emergency residual heat removal system and containment isolation system; The design of the supervision signs includes: (3-2-1) Select symptom parameters, analyze from the aspects of function analysis, probabilistic safety analysis, accident analysis, and system design, and extract symptom parameters corresponding to the functions; (3-2-2) Perform symptom abnormality analysis on symptom parameters and select reasonable abnormal values ​​to characterize the degree of functional degradation; The design of the supervision strategy includes: (3-3-1) A reasonable supervision sequence is formed by determining the supervision principles, which include: First, monitor whether a sodium fire occurs in the power plant and confirm that the sodium fire fighting operation has been performed correctly; Confirm the reliability of the instrumentation and control power supply to ensure the authenticity of the monitoring information used; The priority of safety functions is generally reactivity control, residual heat extraction and radioactivity shielding; Monitoring the availability of dedicated safety facilities; Availability monitoring of critical support systems; (3-3-2) Determine the supervision method and determine the entry, execution and exit criteria of supervision in accordance with the requirements for the parallel implementation of the event-oriented accident handling system and the symptom-oriented accident supervision system and the accident handling coverage; (4) The event-oriented accident handling system and the symptom-oriented accident monitoring system are executed in parallel. Accident diagnosis and response are carried out through the accident handling system, and correction and supplementary operations are carried out through the accident monitoring system, thereby ensuring that accidents are effectively mitigated.

4. The method for designing an accident handling system for a fast reactor nuclear power plant according to claim 3, characterized in that: In step (2), the design of the accident condition list includes: (2-1-1) Determine the list of initiating events of fast reactor nuclear power plants based on the accident analysis results, probabilistic safety analysis (PSA) results and the design characteristics of fast reactor nuclear power plants, including: events included in the accident analysis, key personnel actions and risk-critical tasks determined in the probabilistic safety analysis, and specific events that reflect the typical design characteristics of fast reactors; (2-1-2) Based on the classification of operating conditions and accident handling requirements of fast reactor nuclear power plants, determine the coverage of accident handling of fast reactor nuclear power plants, including: accident conditions from automatic emergency shutdown to core melt, accident conditions of manual emergency shutdown, accident conditions leading to radioactive release, and accident conditions of abnormal fuel operation; (2-1-3) A consequence analysis is conducted for each initiating event. If the accident consequence meets one or more of the covered items, the initiating event is determined to be an accident condition that needs to be handled, thus forming a complete list of accident conditions.

5. The method for designing an accident handling system for a fast reactor nuclear power plant according to claim 3, characterized in that: In step (2), the design of the accident diagnosis strategy includes: (2-2-1) Analyze the evolution process and consequences of the accident for specific accident sequences, and compile the degree of degradation of the safety functions of nuclear power plants and the changing trends of the main characteristic parameters at the early stage of the accident; (2-2-2) Based on the analysis results of the accident evolution process and in combination with the design of fast reactor nuclear power plants, the accident diagnosis criteria under specific accident conditions are formulated and evaluated and analyzed to ensure that the diagnosis criteria are reliable, complete and easy to identify; (2-2-3) By combining the design of fast reactor nuclear power plants with the characteristics and criteria of various specific accidents, and analyzing the independence and degradation degree of accident conditions, an appropriate diagnostic priority order is determined to form an overall accident diagnosis system, and a single-threaded sequential execution method is used to diagnose all conditions in the accident condition list; the diagnostic order is as follows: a) Power loss accidents take precedence over other types of accidents; b) Accidents with high severity take precedence over accidents with low severity; c) High independence of diagnostic criteria takes precedence over low independence of diagnostic criteria.

6. The method for designing an accident handling system for a fast reactor nuclear power plant according to claim 3, characterized in that: In step (2), the design of the accident handling strategy includes: (2-3-1) Conduct extended accident analysis and system analysis and calculations, The extended accident analysis adopts an extended accident analysis based on the best estimation method based on realistic assumptions, and on this basis analyzes the weaknesses of the accident condition response; The system analysis and calculations include design capacity and limit analysis of safety-related systems and equipment, consequence analysis of safety-related systems, and performance analysis of required support systems, in order to evaluate the availability and reliability of measures adopted after an accident; (2-3-2) Develop a strategic framework, including two stages: stabilizing the unit status and retreating to a safe shutdown state: Stabilize the unit status Based on the analysis results of step (2-3-1), combined with the safety functions and system design of the fast reactor nuclear power plant, determine the control and mitigation methods of each safety function of the fast reactor nuclear power plant to achieve stable unit status; Retreat to safe shutdown state The safe retreat state of the unit is determined according to the system configuration state and the requirements for safety functions under specific accident conditions; (2-3-3) Further clarify the policy details through compliance calculation; (2-3-4) Ensure the correctness, availability and integrity of the incident handling strategy through strategy confirmation.

7. The method for designing an accident handling system for a fast reactor nuclear power plant according to claim 6, characterized in that: In step (2), the accident handling strategies determined include: an immediate operation strategy that the operator needs to execute immediately when an accident occurs in the nuclear power plant; a stable operation strategy that brings the nuclear power plant to a normal, stable operating condition or a safe steady-state condition under accident conditions so that the nuclear power plant is in a safe state; and a regular monitoring strategy that regularly checks important parameters and equipment operating status.

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