Equipment grading method based on risk guidance
By adopting a risk-based guidance method in the equipment grading of nuclear power plants, combined with determination theory and probability theory, the problem of equipment grading in the existing technology affects economy and lacks effective risk identification, and the effect of improving economicality and grading credibility while ensuring safety is achieved.
Patent Information
- Application Number
- CN202411814193.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-05-06
AI Technical Summary
The existing nuclear power plant equipment grading method is based on determinism. Although it ensures safety, it affects economics, and lacks effective risk identification and reliability allocation.
The equipment grading method based on risk guidance is adopted, combined with the advantages of traditional determinism and probability theory methods, by building a constraint system for reliability requirements and nuclear safety function requirements, quantifying relevant indicators of nuclear power plants, developing PSA models, identifying design benchmark accidents and other events, conducting risk guidance analysis and in-depth defense assessment, and finally grading equipment based on the originating event response strategy.
On the basis of ensuring the safety of nuclear power plants, improve economics, reduce subsequent design and manufacturing costs through early identification of risks, adapt to diversified grading needs, and improve the credibility of equipment grading.
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Figure CN119940694A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of nuclear power plant item equipment classification, and in particular relates to an equipment classification method based on risk guidance. Background Art
[0002] In the field of nuclear reactor design and safety analysis, two major design concepts have emerged, namely determinism and probabilism. Although these two concepts have a common goal of achieving a certain level of safety, they are different in many aspects, such as how they solve "uncertainty compensation" and the indicators they use to measure the safety level.
[0003] The current classification of nuclear power plant equipment is based on design basis accidents. A deterministic approach is adopted, implemented through traditional defense in depth and a large safety margin. For the classification of nuclear power plant equipment, it may result in matching higher-level equipment to meet the requirements of the initiating event criteria. Although safety is met, it significantly affects economic efficiency. The probabilistic method quantifies the frequency of events / accidents through realistic assumptions and introduces protective measures to make these frequencies acceptably low. Matching equipment items according to frequency can ensure safety while improving economic efficiency through reliability. Combining deterministic and probabilistic methods - risk-guided methods, is of practical significance for the equipment classification of future advanced reactors. Summary of the invention
[0004] The technical problem to be solved by the present invention is to provide a risk-guided equipment classification method that integrates the advantages of traditional deterministic methods and probabilistic methods, and combines reliability allocation technology to guide the classification of future advanced nuclear power equipment, thereby improving economic efficiency while ensuring the safety of nuclear power plants.
[0005] According to one aspect of the present invention, a risk-based device classification method is provided, comprising the following steps:
[0006] Step 1: Establish a reliability requirement and nuclear safety function requirement constraint system;
[0007] Step 2: quantify the relevant indicators of nuclear power plants according to the reliability requirements and nuclear safety function requirements constraint system;
[0008] Step 3: Propose a list of initiating events at nuclear power plants;
[0009] Step 4, developing a PSA model;
[0010] Step 5, identify design basis accidents and conduct deterministic analysis;
[0011] Step 6: Conduct risk guidance analysis on other events;
[0012] Step 7: Conduct defense-in-depth analysis and identify the initiating event;
[0013] Step 8: Classify equipment based on the initiating event response strategy;
[0014] Step 9: Establish a reliability model based on operation requirements, and perform reliability allocation and reliability prediction;
[0015] Step 10: Conduct safety performance demonstration;
[0016] Step 11: Confirm the equipment classification based on the safety demonstration results.
[0017] In step 1, the reliability requirements and nuclear safety function requirements constraint system include reliability requirements and nuclear safety requirements, and the safety function indicators of the nuclear power plant are quantified according to the reliability requirements and the constraint system.
[0018] The reliability includes indicators corresponding to unplanned shutdowns, unplanned power losses, and mean time between failures of equipment; the nuclear safety functions include core damage frequency and radioactive release limits as indicators.
[0019] In step 3, the initiating event list includes three types: expected operational events, design basis events and beyond design basis events, and the three types of events are defined according to their occurrence frequencies.
[0020] In step 4, the PSA model includes a safety-based fault tree and event tree, an economic-based unplanned shutdown fault tree, and a personnel reliability analysis.
[0021] The safety-based event tree starts from the initiating event and is established by determining the event tree header according to the success or failure of each safety function / safety system and personnel intervention; the economic-based unplanned shutdown fault tree establishes a shutdown fault tree model for related systems according to the super component method or the detailed fault tree method; the personnel reliability analysis divides the personnel reliability analysis objects into three categories according to the relationship with the initiating event, namely, personnel behavior before the initiating event, personnel behavior after the initiating event, and personnel behavior leading to the initiating event for analysis.
[0022] The safety-based fault tree model needs to determine the system correlation and then be established according to the fault tree building steps. The system correlation includes functional correlation, correlation of common cause failure components, correlation of human error, correlation of certain functional common components of different systems, and correlation of common support systems of different systems.
[0023] In step 6, the frequency-consequence, quantitative health objectives and risk importance are used to carry out the following: comparing the initiating event with the predetermined frequency-consequence curve to evaluate the risk importance of a single initiating event; quantitative health objective analysis uses the cumulative risk objective to analyze the overall risk of all initiating events to determine the prevention and mitigation of radioactive releases and meet the overall risk criteria; and analyzing the absolute and relative risk importance of single initiating events and items based on frequency-consequence and quantitative health objectives.
[0024] In step 7, a risk-informed defence-in-depth assessment is performed through the definition of initiating events and the identification of important sources of risk uncertainty involved in the frequency-consequence analysis.
[0025] In step 8, the determined initiating events are classified into equipment categories according to the safety response strategies taken in the process of preventing or mitigating the consequences of the events to execute safety functions and support defense-in-depth functions; wherein, the execution of safety functions is classified as a safety-related level, the failure to execute safety functions but having important risks or requiring support for defense-in-depth is classified as a non-safety-related and safety-important level, otherwise it is classified as a non-safety-related and non-safety-important level.
[0026] In step 9, based on the reliability requirements of the normal operation system of the nuclear power plant, reliability modeling is performed on the nuclear power plant equipment, the reliability model is preliminarily allocated and allocation calculations are performed, and reliability prediction is performed based on the allocation calculation results to determine whether the overall reliability requirements are met.
[0027] In step 10, it is confirmed that the equipment classification performed in step 8 meets the reliability requirements after the reliability allocation in step 9, and then the nuclear safety indicators in step 2 are demonstrated to determine whether the safety requirements in step 1 are met.
[0028] After completing step 10, confirm the final risk-informed device classification.
[0029] A technical effect of the present invention is:
[0030] In the embodiment of the present application, first, a reliability requirement and constraint system is constructed; then, the safety function indicators of the nuclear power plant are quantified according to the reliability requirements and constraint system; then, a list of initiating events of the nuclear power plant is proposed; then, a PSA model is developed; then, the design basis accidents are identified and deterministic analysis is carried out; then, risk guidance analysis is carried out for other events; then, a defense-in-depth analysis is carried out and a list of initiating events is determined. Equipment classification is carried out based on the initiating event response strategy; then, a reliability model is established based on the operation requirements, and reliability allocation and reliability prediction are carried out; then, safety performance demonstration is carried out to confirm whether the safety indicators are met; and the equipment classification is confirmed after confirming that the safety requirements are met according to the reliability allocation results.
[0031] Compared with the existing technology that the current nuclear power plant equipment classification is based on determinism and divides the safety level according to the safety functions performed by the items and the importance of their safety functions to ensure nuclear safety, the present invention provides a risk-guided equipment classification method that combines the complementary advantages of determinism and probability theory, and combines reliability allocation technology. On the one hand, it can identify equipment items that cause unplanned shutdowns and classify them according to the shutdown risk contribution, in order to focus on the non-safety-related task requirements of the nuclear power plant itself (such as power generation) to improve the economic efficiency of the nuclear power plant; on the other hand, it can identify risks early in the design stage, which is conducive to more efficient or lower-cost manufacturing in the subsequent stage, thereby reducing costs and increasing efficiency, better adapting to multi-level classification, and meeting the needs of equipment classification from the perspectives of safety and economy. In addition, for some new reactors, when deterministic analysis is adopted, the equipment classification lacks sufficient data support, resulting in the lack of classification credibility required for subsequent design and safety analysis. The use of a risk-guided equipment classification method can complement the advantages of determinism through a probability theory method, making the equipment classification under this method more promising for engineering application. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0033] Figure 1 A schematic flow chart of a risk-based equipment classification method provided by the present invention. DETAILED DESCRIPTION
[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0035] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.
[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0037] According to one aspect of the present invention, a risk-based device classification method is provided, comprising the following steps:
[0038] Step 1: Establish a reliability requirement and nuclear safety function requirement constraint system;
[0039] Step 2: quantify the relevant indicators of nuclear power plants according to the reliability requirements and nuclear safety function requirements constraint system;
[0040] Step 3: Propose a list of initiating events at nuclear power plants;
[0041] Step 4, developing a PSA model;
[0042] Step 5, identify design basis accidents and conduct deterministic analysis;
[0043] Step 6: Conduct risk guidance analysis on other events;
[0044] Step 7: Conduct defense-in-depth analysis and identify the initiating event;
[0045] Step 8: Classify equipment based on the initiating event response strategy;
[0046] Step 9: Establish a reliability model based on operation requirements, and perform reliability allocation and reliability prediction;
[0047] Step 10: Conduct safety performance demonstration;
[0048] Step 11: Confirm the equipment classification based on the safety demonstration results.
[0049] In the embodiments of the present application, reliability and safety indicators are constructed, a PSA model is developed, deterministic and risk guidance methods are used, and reliability allocation technology is combined to perform equipment classification after the initiating event is determined.
[0050] Therefore, this equipment classification method can guide designers to carry out classification design of nuclear power plant equipment.
[0051] Specifically, by determining the reliability and nuclear safety constraint indicators of nuclear power plants, developing PSA models around the indicators and conducting risk guidance analysis, the corresponding equipment classification is carried out after the initiating event is determined. According to the classification results, reliability allocation and prediction are carried out by establishing a reliability model to prove that the classification results combined with reliability allocation meet the indicator requirements and meet the needs of equipment classification from two perspectives: reliability improvement of nuclear power plant economy and nuclear safety.
[0052] In step 1, the reliability requirements and nuclear safety function requirements constraint system includes reliability requirements and nuclear safety requirements.
[0053] For nuclear power plants, the equipment classification should be based on the following reliability and nuclear safety function requirements and constraints, including the execution of reactivity control, residual heat removal, radioactive containment safety functions, and meeting the reliability and economic requirements of defense in depth and nuclear power plants.
[0054] Relevant systems of nuclear power plants used to meet the above objectives are preliminarily screened through design documents, engineering design experience, etc., in order to summarize and classify the design functions of the systems.
[0055] In step 2, the safety function indicators of the nuclear power plant are quantified according to the reliability requirements and constraint system. The reliability requirements correspond to the indicators of unplanned shutdown, unplanned power loss, and mean time between failures of equipment.
[0056] Nuclear safety functions require core damage frequency and radioactive release limits as indicators.
[0057] In step 3, a list of initiating events is proposed.
[0058] Based on the experience of reactor engineering design and nuclear power plant license application documents, system failure mode and effect analysis (FMEA), operation study report and experience feedback, main logic diagram method, etc., a set of initiating event lists are proposed. Including three types of expected operation events, design basis events (including design basis accidents) and beyond design basis events. The three types of events are defined according to the frequency of occurrence. For example, if the frequency of occurrence of expected operation events is 10 -2 ~1 / reactor-year. The design basis event frequency is 10 -4 ~10 -2 / reactor year. The frequency of occurrence of beyond design basis events is less than 10 -4 / Heap-year, but a lower frequency limit will be defined.
[0059] Step 4: Develop the PSA model.
[0060] The PSA model includes safety-based fault trees and event trees, economic (power generation)-based unplanned outage fault trees, and human reliability analysis.
[0061] Safety-based event tree model. After the initiating event list is determined in step 3, the response of the nuclear power plant to each initiating event group is analyzed to determine the event sequence that may cause core damage or remove residual heat after the reactor is shut down to put the nuclear power plant in a safe state. That is, starting from the initiating event, a safety-based event tree model is established according to the success or failure of each safety function / safety system and personnel intervention.
[0062] In the safety-based event tree model, different from the two-state model where the system is either successful or failed, in order to further improve the economy, the system may be partially successful and partially failed in the intermediate state in the current project, and reasonable simplification is carried out using the correlation between the initiating event and the mitigation system, the time correlation of the mitigation system, the time segmentation correlation in the accident process, the common cause failure of the equipment and other nuclear power plant-specific correlations. The simplification method includes the following: the success or failure of the event tree header does not affect the consequences of the event sequence; the hardware of the header system has been shown to be unable to operate in the previous section, and the subsequent header does not need to branch; the operation of the header system does not contribute to the required safety functions, etc.
[0063] Safety-based fault tree model. Establish a system fault tree model according to the fault tree building steps. First, conduct a quantitative analysis on the system model to check the correctness of the system model and check whether there are weak links in the design. Then connect the system model to the fault tree models of all supporting systems and quantify the combined model to conduct a comprehensive reliability evaluation of the system.
[0064] The fault tree model needs to determine the system correlation, including functional correlation, correlation of common cause failure components (perform common cause failure analysis), correlation of human error (perform personnel reliability analysis), correlation of certain functional common components of different systems (use the same coding for the same component and the same failure), and correlation of common support systems of different systems (consider the combination of event tree and fault tree). The special type of initiating event fault tree and trigger signal failure are considered in the fault tree model.
[0065] Unplanned outage fault tree based on economics (power generation). For related systems, establish an outage fault tree model according to the super component method (the system and sequence are regarded as a single component in the nuclear power plant) or the detailed fault tree method (modeling of individual system components and their potential failures). Quantify the model and compare the quantified results with the empirical feedback data for result analysis and processing.
[0066] According to the relationship with the initiating event, personnel reliability analysis divides the objects of personnel reliability analysis into three categories: personnel behavior before the initiating event (involved in the fault tree), personnel behavior after the initiating event (reflected in the event tree and fault tree), and personnel behavior leading to the initiating event (immediate diagnostic behavior after the accident and intervention operation behavior according to procedures after diagnosis).
[0067] The personnel behavior before the initiating event is involved in the fault tree, and the probability of error can refer to the empirical value of probabilistic safety assessment of nuclear power plants of the same type.
[0068] The personnel behavior after the initiating event is reflected in the event tree and fault tree. The personnel response after the accident in the fault tree involves the start and stop of the backup equipment; the personnel response after the accident in the event tree includes the immediate diagnosis after the accident and the intervention operation behavior after diagnosis. The probability of diagnostic error in the diagnosis stage is carried out by the HCR method. The error probability of intervention operation behavior after diagnosis is carried out by the THERP method.
[0069] The human behavior that led to the initiating event is determined by statistical means, such as an unplanned shutdown caused by human error.
[0070] Step 5 identifies the design basis accidents in the initiating events and conducts deterministic analysis. Design basis accidents are identified by the method that their safety functions are performed only by safety-related items, and all safety-irrelevant items performing the same safety functions are unavailable.
[0071] Deterministic analysis uses conservative assumptions, takes into account appropriate uncertainties, and defines equipment requirements and specifies operating limits to demonstrate that the results meet the requirements of the guidelines.
[0072] Step 6 is to conduct risk-informed analysis of other events in the initiating event, using frequency-consequence, quantitative health objectives and risk importance.
[0073] The PSA results of initiating events are evaluated according to the frequency-consequence objectives, taking into account the event sequence corresponding to the frequency quantile values required by the nuclear power plant in the PSA results to exclude the steep edge effect. The initiating events are compared with the frequency-consequences to evaluate the risk importance of individual initiating events. Based on the mean consequence, the DBE dose is evaluated according to the frequency-consequence objectives. The purpose of the frequency-dose assessment is to ensure that initiating events involving radioactive releases do not make a significant contribution to the risk.
[0074] The quantitative health objective analysis analyzes the overall risk of all initiating events using cumulative risk objectives to determine the prevention and mitigation of radioactive releases and meet overall risk criteria.
[0075] Analyze the absolute and relative risk importance of individual initiating events and items based on frequency-consequence and quantitative health objectives, thereby supporting risk-informed defense-in-depth assessments.
[0076] In step 7, a risk-informed defence-in-depth assessment is conducted through the definition of initiating events and the identification of important sources of risk involving uncertainty in the frequency-consequence analysis.
[0077] Through steps 4-6, confirm the final list of events that need to be analyzed from the initial list of events proposed in step 3.
[0078] In step 8, the equipment is classified according to the safety response strategies taken in the process of preventing or mitigating the consequences of the identified initiating events to perform safety functions and support the in-depth defense function. Among them, the equipment that performs safety functions is classified as safety-related, the equipment that does not perform safety functions but has important risks or needs to support in-depth defense is classified as non-safety-related and safety-important, and otherwise it is classified as non-safety-related and non-safety-important.
[0079] In step 9, based on the reliability requirements of the normal operation system of the nuclear power plant, reliability modeling is performed on the nuclear power plant equipment, and the reliability model is preliminarily allocated and the allocation calculation is performed.
[0080] Five influencing factors are considered in reliability allocation: equipment complexity, reliability, nuclear safety importance, environment and time.
[0081] Reliability prediction is performed based on the distribution calculation results to determine whether the overall reliability requirements are met.
[0082] Step 10 is to demonstrate safety performance. After confirming that the equipment classification in step 8 meets the reliability requirements after the reliability allocation in step 9, the nuclear safety indicators in step 2 are demonstrated to determine whether the safety requirements in step 1 are met.
[0083] In step 11, after completing step 10, the final risk-based device classification is confirmed.
[0084] 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.
[0085] 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 risk-based equipment classification method, characterized in that: The steps include: Step 1: Establish a reliability requirement and nuclear safety function requirement constraint system; Step 2: quantify the relevant indicators of nuclear power plants according to the reliability requirements and nuclear safety function requirements constraint system; Step 3: Propose a list of initiating events at nuclear power plants; Step 4, developing a PSA model; Step 5, identify design basis accidents and conduct deterministic analysis; Step 6: Conduct risk guidance analysis on other events; Step 7: Conduct defense-in-depth analysis and identify the initiating event; Step 8: Classify equipment based on the initiating event response strategy; Step 9: Establish a reliability model based on operation requirements, and perform reliability allocation and reliability prediction; Step 10: Conduct safety performance demonstration; Step 11: Confirm the equipment classification based on the safety demonstration results.
2. The risk-based equipment classification method according to claim 1 is characterized in that: In step 1, the reliability requirements and nuclear safety function requirements constraint system include reliability requirements and nuclear safety requirements, and the safety function indicators of the nuclear power plant are quantified according to the reliability requirements and the constraint system.
3. The risk-based equipment classification method according to claim 2 is characterized in that: The reliability includes indicators corresponding to unplanned shutdowns, unplanned power losses, and mean time between failures of equipment; the nuclear safety functions include core damage frequency and radioactive release limits as indicators.
4. The risk-based equipment classification method according to claim 1, characterized in that: In step 3, the initiating event list includes three types: expected operational events, design basis events and beyond design basis events, and the three types of events are defined according to their occurrence frequencies.
5. The risk-based equipment classification method according to claim 1, characterized in that: In step 4, the PSA model includes a safety-based fault tree and event tree, an economic-based unplanned shutdown fault tree, and a personnel reliability analysis.
6. The risk-based equipment classification method according to claim 5 is characterized in that: The safety-based event tree starts from the initiating event and is established by determining the event tree header according to the success or failure of each safety function / safety system and personnel intervention; the economic-based unplanned shutdown fault tree establishes a shutdown fault tree model for related systems according to the super component method or the detailed fault tree method; the personnel reliability analysis divides the personnel reliability analysis objects into three categories according to the relationship with the initiating event, namely, personnel behavior before the initiating event, personnel behavior after the initiating event, and personnel behavior leading to the initiating event for analysis.
7. The risk-based equipment classification method according to claim 6 is characterized in that: The safety-based fault tree model needs to determine the system correlation and then be established according to the fault tree building steps. The system correlation includes functional correlation, correlation of common cause failure components, correlation of human error, correlation of certain functional common components of different systems, and correlation of common support systems of different systems.
8. The risk-based equipment classification method according to claim 7 is characterized in that: In step 6, the frequency-consequence, quantitative health target and risk importance are specifically carried out as follows: the initiating event is compared with a predetermined frequency-consequence curve to evaluate the risk importance of a single initiating event; Quantitative health objective analysis uses cumulative risk objectives to analyze the overall risk of all initiating events to determine the prevention and mitigation of radioactive releases and meet overall risk criteria; Analyze the absolute and relative risk importance of individual initiating events and items based on frequency-consequence and quantitative health objectives.
9. The risk-based equipment classification method according to claim 8, characterized in that: In step 7, a risk-informed defence-in-depth assessment is performed through the definition of initiating events and the identification of important sources of risk uncertainty involved in the frequency-consequence analysis.
10. The risk-based equipment classification method according to claim 9, characterized in that: In step 8, the determined initiating events are classified into equipment categories according to the safety response strategies taken in the process of preventing or mitigating the consequences of the events to execute safety functions and support defense-in-depth functions; wherein, the execution of safety functions is classified as a safety-related level, the failure to execute safety functions but having important risks or requiring support for defense-in-depth is classified as a non-safety-related and safety-important level, otherwise it is classified as a non-safety-related and non-safety-important level.
11. The risk-based equipment classification method according to claim 10, characterized in that: In step 9, based on the reliability requirements of the normal operation system of the nuclear power plant, reliability modeling is performed on the nuclear power plant equipment, the reliability model is preliminarily allocated and allocation calculations are performed, and reliability prediction is performed based on the allocation calculation results to determine whether the overall reliability requirements are met.
12. The risk-based equipment classification method according to claim 11, characterized in that: In step 10, it is confirmed that the equipment classification performed in step 8 meets the reliability requirements after the reliability allocation in step 9, and then the nuclear safety indicators in step 2 are demonstrated to determine whether the safety requirements in step 1 are met.
13. The risk-based equipment classification method according to claim 12, characterized in that: After completing step 10, confirm the final risk-informed device classification.