Design method for critical safety function recovery strategy of nuclear power plant based on symptom

Abstract

The present invention relates to a design method for a symptom-based nuclear power plant critical safety function recovery strategy, comprising: (1) determining the accident condition class corresponding to the critical safety function; (2) determining the sub-function set for mitigating and controlling the critical safety function; (3) determining the systems and equipment in the sub-function set, and performing characteristic analysis of the systems and equipment in the sub-function set; (4) performing a critical path analysis, and determining the priority sequence of the critical path for mitigating the critical safety function; (5) obtaining the corresponding critical safety function mitigation strategy based on the priority sequence of the critical path for mitigating the critical safety function, and verifying the feasibility of the strategy. The critical safety function mitigation strategy designed according to the present invention provides the operator with the best operation sequence during accident handling, avoids the operator's accident handling delay caused by executing a mitigation sequence with low reliability during the accident handling process, and better reflects the advancement and safety of the strategy design.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant design, and in particular relates to a design method for a key safety function recovery strategy of an accident nuclear power plant based on symptom. Background Art

[0002] The design of nuclear power plants is complex, involving a wide variety of systems and equipment. The number of initial causes that may lead to accidents is huge. If response strategies are formulated for each of them, the number will be huge. The symptom-based accident procedures can achieve the purpose of controlling and mitigating the consequences of accidents by controlling the key safety functions of nuclear power plants affected after the accident. It can effectively handle complex working conditions and superimposed accidents and is the most widely used advanced accident handling method in the world. Compared with the simple event-based accident procedure system, the symptom-based accident procedure system increases the depth of defense of the procedures and can better ensure the nuclear safety of power plants. The key safety function recovery strategy is the core of the symptom-based accident procedure. Whether its design is reasonable directly affects the accuracy and speed of the symptom-based accident procedure in handling accidents.

[0003] There are often large differences in system design between different reactor types in nuclear power plants, especially pressurized water reactor nuclear power plants. Therefore, for nuclear power plants of different reactor types, different key safety function mitigation strategies need to be determined based on different design features. The so-called key safety function refers to the function that directly affects the nuclear safety of the unit under accident conditions, such as core cooling. On the other hand, even for different units of the same reactor type, the continuous implementation of unit improvement items may cause changes in system design, which in turn may lead to changes in the control and mitigation measures of the key safety functions of the unit, thereby affecting the design of the key safety function strategy framework and design values. For this, it is also necessary to analyze and determine its operation strategy in combination with the design characteristics of the improved unit to improve the accuracy and speed of handling accidents. The key safety function recovery strategy of the symptom-oriented accident guideline involves a large number of systems and equipment in nuclear power plants. The various steps of the strategy are mutually influential and related, and need to be analyzed and determined based on scientific and reasonable design methods. Summary of the invention

[0004] The purpose of the present invention is to provide a design method for a symptom-based accident nuclear power plant key safety function recovery strategy, so as to obtain the optimal symptom-oriented key safety function recovery strategy based on different nuclear power unit designs, so as to better reflect its advancement and safety.

[0005] The technical solution of the present invention is as follows: A design method for a key safety function recovery strategy for an accident nuclear power plant based on symptoms, comprising the following steps:

[0006] (1) Determine the accident conditions corresponding to the key safety functions;

[0007] (2) Determine the signs of accidents in each accident condition through accident analysis, and determine the sub-function sets for mitigation and control of key safety functions;

[0008] (3) Determine the systems and equipment in the sub-function set and analyze the characteristics of the systems and equipment in the sub-function set;

[0009] (4) Conduct critical path analysis to determine the priority sequence of critical paths for mitigating critical safety functions;

[0010] (5) According to the priority sequence of the key safety function mitigation critical path, the corresponding key safety function mitigation strategy is obtained and the feasibility of the strategy is verified.

[0011] Furthermore, in the design method of the critical safety function recovery strategy for a nuclear power plant based on symptom-based accidents as described above, in step (1), based on the design characteristics of the unit and the range of accident conditions covered by the unit accident procedures, the range of accident conditions corresponding to specific critical safety functions is determined by analyzing the core physics and thermal-hydraulic characteristics under accident conditions.

[0012] Furthermore, in the design method of the critical safety function recovery strategy for a nuclear power plant based on a symptom-based accident as described above, in step (3), the characteristic analysis of the system and equipment includes functional analysis, equipment safety analysis, equipment reliability analysis, mitigation measure redundancy analysis, and support system analysis, and based on the analysis, the effects of mitigation and control of critical safety functions are normalized, their corresponding weights are calibrated, and the priority sequence of different system equipment in the same sub-function is determined based on the calibrated weights.

[0013] Furthermore, in the above-mentioned design method of the critical safety function recovery strategy of the nuclear power plant based on the symptom-based accident, in step (4), the sub-function sets for mitigation and control of the critical safety functions determined in step (2) are arranged to form a critical path; and based on the weights and priority sequences of different system equipment determined in step (3), the weight assignments of each critical path are analyzed and determined, and then the priority sequence of the critical paths for mitigation of the critical safety functions is determined.

[0014] Furthermore, in the design method of the symptom-based accident nuclear power plant key safety function recovery strategy as described above, if the verification and confirmation result in step (5) does not meet the acceptance criteria requirements, the strategy formulation process should be returned to the beginning and the accident analysis and design analysis should be repeated.

[0015] The beneficial effects of the present invention are as follows:

[0016] 1. The present invention is applicable to different reactor types including pressurized water reactor nuclear power plants, and provides a design method for the development of key safety function mitigation strategies in symptom-guided accident procedures for different reactor types.

[0017] 2. The critical safety function mitigation strategy designed according to the method of the present invention can effectively cover the coverage of the power plant accident regulations, ensuring that there will be no situation where a certain accident condition has no corresponding critical safety function mitigation strategy.

[0018] 3. The present invention proposes for the first time a design method for determining sub-function set weight factors by analyzing system equipment, and innovatively proposes a method for quantitatively analyzing sub-function set priorities.

[0019] 4. The present invention proposes for the first time a method for determining the critical path for mitigation of key safety functions and performing quantitative analysis through the critical path weights. Based on this quantitative analysis method, the priority analysis problem of mitigation of key safety functions can be effectively solved.

[0020] 5. The critical safety function mitigation strategy designed according to the method of the present invention provides the operator with the best operation sequence when handling an accident, thereby avoiding delays in accident handling caused by the operator executing a mitigation sequence with low execution reliability during the accident handling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flowchart of a method for designing a mitigation strategy for critical safety functions of the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0023] The design of nuclear power plants is complex, involving a large number of systems and equipment, and the number of initial causes of possible accidents is very large. The symptom-based method controls the unit status by controlling and mitigating key safety functions. Therefore, the control and mitigation of key safety functions is one of the characteristics of the symptom-based method accident handling procedures, and its corresponding mitigation and control strategies are crucial to the effect of nuclear power plant accident handling.

[0024] On the premise of clarifying the key safety functions of the target nuclear power unit, the following issues need to be addressed in formulating reasonable mitigation and control strategies for key safety functions:

[0025] Identify accident conditions that may cause degradation of specific critical safety functions

[0026] The range of accident conditions that a nuclear power plant can cope with is relatively large. For a specific critical safety function, not all accident conditions will cause the critical safety function to deteriorate. Therefore, in order to formulate the mitigation and control strategy for the critical safety function, it is necessary to first screen and determine the accident conditions that need to be mitigated and controlled.

[0027] Identify controls for critical safety functions

[0028] The key safety function of a nuclear power plant is a relatively macro concept. To specify mitigation and control strategies for it, it is necessary to further analyze it, clarify it to specific systems and equipment, and determine its priority for commissioning.

[0029] Mitigating critical paths for key safety functions

[0030] The critical path for mitigating and controlling key safety functions usually involves the control and mitigation of multiple sub-functions. The time left for operators to operate under accident conditions is often more urgent, and the probability of human error in operation is higher than that in daily operations. The strategies with high priority and high reliability should be implemented first in the accident procedures. Therefore, how to determine the sub-functions required for the critical path and the priorities of different critical paths directly affect the design of the mitigation strategy for key safety functions.

[0031] In view of the above technical problems to be solved, the present invention proposes a design method for a key safety function recovery strategy for an accident nuclear power plant based on symptoms. The method flow is as follows: Figure 1 As shown, the following steps are included:

[0032] (1) Determine the accident conditions corresponding to the key safety functions.

[0033] Nuclear power plants are complex in design, with numerous systems and equipment. Therefore, there are many types of accidents that may occur in nuclear power plants. Different accidents may cause different consequences, that is, the key safety functions affected in different accident consequences are not the same. For example, in the main steam pipe rupture accident of a certain type of pressurized water reactor nuclear power plant, the key safety functions affected include the main system integrity, containment integrity, core subcriticality, etc., while the key safety functions affected in the SGTR accident, in addition to the main system integrity, also affect core cooling, etc. Therefore, it is necessary to determine the accident condition range corresponding to a specific key safety function based on the accident condition range covered by the unit accident regulations by analyzing the core physics and thermal-hydraulic characteristics under accident conditions. Determine the mitigation strategy corresponding to the key safety function through targeted analysis.

[0034] (2) Identify sub-function sets that mitigate and control critical security functions.

[0035] After determining the accident condition type EL1 corresponding to a specific critical safety function, determine the signs after the accident in EL1 through accident analysis. Based on the design characteristics of the unit (such as the design of special safety facilities for the unit, etc.), determine the sub-function GA of the unit design used to mitigate and control the critical safety functions in the accident (the sub-functions are clearly defined in the symptom-oriented accident procedures). For example, for a certain type of pressurized water reactor nuclear power plant SGTR accident, the accident analysis determined that after its occurrence, it would cause the evaporator water level to rise, and the radioactivity was abnormal, the pressurizer water level to decrease, and other signs corresponding to the deterioration of the critical safety function core cooling. Based on the above signs and the design characteristics of the nuclear power plant, it was determined that the sub-functions of the critical safety function of mitigating core cooling include the primary water charge control sub-function, the evaporator sub-function, etc.

[0036] (3) Sub-function set system equipment analysis.

[0037] After completing the analysis of the sub-function set of key safety functions, it is necessary to further determine the systems and equipment in the sub-function set. Analyze and determine the characteristics of the systems and equipment in the same sub-function. The analysis should include functional analysis, equipment safety classification, equipment reliability analysis, mitigation measures redundancy analysis, support system analysis, etc. Based on the above analysis, the role of system equipment in mitigating and controlling key safety functions is normalized and its corresponding weight is calibrated. The calibration weight value is fx = fx1*fx2*fx3…fxy (where x corresponds to the system or equipment code and y corresponds to the analysis type). Based on the system characteristic calibration weight size, the priority sequence of different system equipment in the same sub-function (f1, f2, f3…fx) is determined. For example, for the key safety function of core cooling of a certain type of pressurized water reactor nuclear power plant, the priority sequence of the systems and equipment involved in the primary water installation sub-function set includes the emergency core injection system, the upper charging and lowering system, the boron and water supply system, etc.

[0038] (4) Critical path analysis to determine the priority sequence of critical paths for mitigating key safety functions.

[0039] Based on the sub-function GA of controlling and mitigating the critical safety function G determined in step (2), since each critical safety function includes multiple sub-functions, and each sub-function includes different system equipment, in order to mitigate the critical safety function, the different system equipment in the sub-function can be arranged to form a critical path KPx (x = 1, 2, 3...). Based on the weights and priority sequence of different system equipment determined by the sub-function set system equipment analysis in step (3), the weight assignment KPfx of each critical path can be analyzed and determined, and then the priority sequence of the critical path mitigation of the critical safety function can be determined. For example, for the core cooling of a certain type of pressurized water reactor nuclear power plant, the sub-function analysis determines that its sub-function includes the primary circuit water loading and heat sink. Combined with the analysis of its sub-function system and equipment, its critical path at least includes emergency core cooling + evaporator, emergency core cooling + residual heat removal system, upper charging and lowering / boron and water supply system + evaporator, upper charging and lowering / boron and water supply system + residual heat removal system, etc. The weight assignment obtained through system and equipment analysis can be used to rank the critical paths for mitigation of key safety functions.

[0040] (5) Verification, confirmation and finalization of mitigation strategies for key safety functions.

[0041] Based on the analysis conclusions in step (4), the corresponding key safety function mitigation strategy is combined according to the key safety function mitigation critical path priority sequence. Combined with the key safety function corresponding to the accident condition EL1, verify whether the strategy is feasible. The verification and confirmation process should also include aspects such as human factors verification. If the verification and confirmation results do not meet the acceptance criteria requirements, it should return to the beginning of the strategy formulation process and re-perform accident analysis and design sorting and other analyses.

[0042] Example

[0043] This example illustrates the specific implementation of the key safety function mitigation strategy design method of the present invention:

[0044] 1) Based on the design characteristics of a certain type of nuclear power plant, the scope of accidents covered by accident procedures, accident analysis conclusions and key safety functions, the accident condition category EL1 corresponding to the key safety function core cooling is determined, including accident conditions such as SGTR, LOCA, and SLB.

[0045] 2) According to the conclusions of the accident analysis such as SGTR, as well as the design characteristics of the unit, the sub-function set of core cooling mitigation is determined to include the main system water charge GA1 and the heat sink GA2.

[0046] 3) Through the analysis of different sub-function sets, determine the list of systems and equipment involved, among which the systems and equipment corresponding to the restoration of the main system water charge are GA11, GA12...GA1n, and the systems and equipment corresponding to the restoration of the heat sink are GA21, GA22...GA2m. Determine the weight factor GAF of the systems and equipment involved in the sub-function set for core cooling relief xy (x, y are the corresponding sub-function set numbers);

[0047] 4) Determine the critical path matrix based on the conclusions in step 2):

[0048]

[0049] 5) Based on the conclusions in step 3) and step 4), the core cooling mitigation weights are assigned to the critical paths, and the execution priority ranking (K1, K2…Knm) is completed.

[0050] 6) Based on the conclusions of step 5), a mitigation strategy for the key safety functions of core cooling is formed.

[0051] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A design method for a critical safety function recovery strategy for a nuclear power plant based on symptoms, comprising the following steps: (1) Determine the accident condition category corresponding to the key safety function. According to the unit design characteristics and the accident condition range covered by the unit accident procedures, determine the accident condition range corresponding to a specific key safety function by analyzing the core physical and thermal hydraulic characteristics under accident conditions; (2) Determine the signs of accidents in each accident condition through accident analysis, and determine the sub-function sets for mitigation and control of key safety functions; (3) Determine the systems and equipment in the sub-function set, and conduct characteristic analysis of the systems and equipment in the sub-function set, including functional analysis, equipment safety analysis, equipment reliability analysis, mitigation measure redundancy analysis, and support system analysis. Based on the characteristic analysis of the systems and equipment, normalize the role of mitigation and control of key safety functions, calibrate their corresponding weights, and determine the priority sequence of different system equipment in the same sub-function based on the calibrated weights; (4) Perform critical path analysis to determine the priority sequence of critical paths for mitigating critical safety functions, and arrange the critical paths based on the sub-function sets of mitigation and control of critical safety functions determined in step (2); Based on the weights and priority sequences of different system devices determined in step (3), analyze and determine the weight assignments of each critical path, and then determine the priority sequence of the critical paths for mitigation of key safety functions; (5) According to the priority sequence of the key safety function mitigation critical path, the corresponding key safety function mitigation strategy is obtained and the feasibility of the strategy is verified.

2. The method for designing a symptom-based accident critical safety function recovery strategy for a nuclear power plant according to claim 1, characterized in that: If the verification and confirmation results in step (5) do not meet the acceptance criteria, then the process should return to the beginning of the strategy formulation process and re-analyze the incident and design.

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