Evaluation method for mobile equipment configuration in nuclear power bases based on multi-unit safety assessment

Abstract

The present invention belongs to the technical field of evaluation methods, and specifically relates to a method for evaluating the configuration of mobile equipment in a nuclear power base based on multi-unit safety evaluation. The method comprises the following steps: Step 1: Modeling the mobile equipment, using PSA software to add the mobile equipment to the event tree and fault tree of the single-unit PSA model, and analyzing the time of mobile equipment intervention and personnel reliability events; Step 2: Using PSA software to establish a MUPSA model; Step 3: Setting up a sensitivity analysis case and performing calculations; Step 4: Using the calculation results to analyze risk changes and preliminarily select a configuration plan; Step 5: Combining factors such as configuration maintenance cost, availability, and comprehensive emergency dispatch to conduct a multi-objective comprehensive optimization analysis and further screen the configuration plan; Step 6: Based on the screened configuration plan, an evaluation of the existing configuration of the nuclear power base and configuration recommendations are given. The beneficial effect is that it can effectively solve the problem of a lack of sufficient theoretical analysis basis and a lack of a systematic and effective configuration evaluation method when configuring mobile equipment in nuclear power bases.

Description

Technical Field

[0001] The present invention belongs to the technical field of evaluation methods, and in particular relates to a nuclear power base mobile equipment configuration evaluation method based on multi-unit safety evaluation. Background Art

[0002] Mobile equipment at nuclear power bases includes emergency diesel generators, mobile pumps, fire trucks, and mobile hydrogen removal systems. These mobile equipment plays a vital role in preventing and mitigating severe multi-unit accidents. Multi-unit severe accidents are a significant factor affecting the safety of multi-unit nuclear power bases, and multi-unit severe accident analysis plays a key role in safety assessments against severe external disasters and damage.

[0003] Like most nuclear power bases internationally, my country's nuclear power bases are composed of multiple units. Therefore, multi-unit safety analysis is crucial for improving the safety of these bases. Furthermore, the configuration of mobile equipment varies across different nuclear power bases, and the industry lacks mature configuration evaluation methods and systems.

[0004] After years of application experience both domestically and internationally, probabilistic safety assessment (PSA) technology has been proven to be an effective technique for evaluating power plant safety performance from a probabilistic perspective and mathematically identifying safety weaknesses. Multi-unit probabilistic safety assessment (MUPSA) technology is a research area in its infancy both domestically and internationally. Research on MUPSA will help integrate existing technologies, including Level 1 internal event PSA, Level 1 external event PSA, and Level 2 PSA, and will contribute to the overall advancement of risk-informed technology applications.

[0005] Using MUPSA technology to evaluate and analyze the configuration of mobile equipment at multi-unit nuclear power bases can provide reliable quantitative parameters. This analysis quantitatively evaluates the configuration of mobile equipment at a multi-unit nuclear power base through CDF / LERF analysis. By combining this quantitative analysis with other qualitative analyses, we can provide mobile equipment configuration plans and recommendations for a specific multi-unit nuclear power base. Summary of the Invention

[0006] In view of the current situation that domestic nuclear power bases lack sufficient theoretical analysis basis and systematic and effective configuration evaluation methods when configuring mobile equipment, the purpose of the present invention is to provide a nuclear power base mobile equipment configuration evaluation method based on multi-unit safety evaluation, which can evaluate whether the mobile equipment configuration of a nuclear power base meets the overall nuclear safety requirements, and determine whether it is necessary to add mobile equipment to the nuclear power base through analysis results.

[0007] The technical solution of the present invention is as follows: A method for evaluating the configuration of mobile equipment in a nuclear power base based on multi-unit safety evaluation comprises the following steps:

[0008] Step 1: Model the mobile equipment and use PSA software to add the mobile equipment to the event tree and fault tree of the single-unit PSA model. Analyze the time of mobile equipment intervention and personnel reliability events.

[0009] Step 2: Use PSA software to establish the MUPSA model;

[0010] Step 3: Set up a sensitivity analysis case and perform calculations;

[0011] Step 4: Use the calculation results to analyze risk changes and preliminarily select a configuration plan;

[0012] Step 5: Conduct a multi-objective comprehensive optimization analysis based on factors such as configuration maintenance cost, availability, and comprehensive emergency dispatch to further screen configuration solutions.

[0013] Step 6: Provide an evaluation of the existing configuration of the nuclear power base and configuration recommendations based on the selected configuration options.

[0014] In step 1, the models of mobile equipment that need to be modeled include the first-level internal event PSA model, the first-level external event PSA model, the second-level PSA model, and the spent pool PSA model. The specific modeling interface is based on the reactor type and the power plant modification items. For the mobile emergency diesel generator, the modeling interface is located after the unit's emergency diesel generator fails; for the mobile water supply pump, the modeling interface is located at the first and second circuit emergency water supply interfaces. The reliability data of the mobile equipment is the fitted value of the power plant's historical data and the equipment's general data. The CBDTM method is selected in the cognitive stage, and the THERP method is selected in the execution stage. SPRA-H is used for comprehensive time series analysis, and the personnel tension is always high.

[0015] In step 2, the ratio of multiple unit models of the plant-level MUPSA is based on the actual situation of the nuclear power base, ensuring that the units of the same reactor type are in the same model, the upper limit of the ratio of the number of MUPSA model units for a single-stack arrangement is 4, and the upper limit of the ratio of the number of MUPSA model units for a dual-stack arrangement is 2.

[0016] In step 3, the setting of the sensitivity calculation examples of independent analysis corresponds to the number of different types of mobile equipment from 0 to N, where N is the number of units in the nuclear power base, and the sensitivity calculation examples of combined analysis are set. In order to reduce the amount of calculation, the sensitivity calculation examples of the combined analysis are set based on the existing configuration plan of the nuclear power base.

[0017] In step 4, the risk change assessment consists of two parts: a forward verification method of the risk analysis and assessment and a reverse verification method of the risk analysis and assessment.

[0018] The forward verification method assumes that additional mobile devices are to be added, and analyzes how many additional mobile devices will bring about greater risk improvement benefits.

[0019] The reverse verification method analyzes whether it is necessary to increase the additional number under the premise of obtaining the additional number of forward verification.

[0020] In step 5, a four-objective optimization model is established, namely, minimizing risk criteria, minimizing configuration and maintenance costs, maximizing availability, and maximizing available time for emergency dispatch. The NSGA-II algorithm is used to take the Pareto optimal solution as the comprehensive optimization analysis plan, and the intersection of the Pareto optimal solution and the preliminary configuration plan is taken as the final configuration recommendation in step 6.

[0021] The beneficial effects of the present invention are that the nuclear power base mobile device configuration evaluation method described in the present invention can effectively solve the problem that domestic nuclear power bases lack sufficient theoretical analysis basis and lack systematic and effective configuration evaluation methods when configuring mobile devices, which helps nuclear power bases to configure mobile devices according to analysis and evaluation conclusions, improve the overall safety of nuclear power bases while controlling the configuration cost of mobile devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a specific implementation flow chart of a method for evaluating the configuration of mobile equipment in a nuclear power base based on multi-unit probabilistic safety assessment according to embodiment 1 of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] This paper uses the calculation results of the MUPSA model as the primary mobile equipment configuration evaluation metric, using the calculated CDF / LERF ratio as the basis for quantitative analysis. The impact of MUPSA on the plant-wide MUCDF / MULERF ratio is also calculated. The calculation results are quantitatively analyzed using four configuration analysis methods, including forward and reverse validation. This approach combines qualitative screening and analysis of initiating events based on external event screening with comprehensive optimization analysis based on a multi-objective optimization algorithm to ultimately determine mobile equipment configuration evaluation results for the target nuclear power base. Based on this, standard recommendations for mobile equipment configuration are provided.

[0025] The method for evaluating the configuration of mobile equipment for a nuclear power base based on multi-unit safety evaluation includes the following steps:

[0026] Step 1: Model the mobile equipment and use the PSA software to add the mobile equipment to the event tree and fault tree of the single-unit PSA model, and analyze the time of mobile equipment intervention and personnel reliability events.

[0027] Step 2: Use PSA software to establish the MUPSA model.

[0028] Step 3: Set up a sensitivity analysis case and perform calculations.

[0029] Step 4: Use the calculation results to analyze risk changes and preliminarily select a configuration plan.

[0030] Step 5: Conduct a multi-objective comprehensive optimization analysis based on factors such as configuration maintenance cost, availability, and comprehensive emergency dispatch to further screen configuration solutions.

[0031] Step 6: Provide an evaluation of the existing configuration of the nuclear power base and configuration recommendations based on the selected configuration options.

[0032] In step 1, the models of mobile equipment that need to be modeled include the first-level internal event PSA model, the first-level external event PSA model (at least including earthquakes, external flooding, and external fires), the second-level PSA model, and the spent pool PSA model. The specific modeling interface is based on the reactor type and the power plant modification items. Generally, for mobile emergency diesel generators, the modeling interface is located after the unit's emergency diesel generator fails; for mobile water supply pumps, the modeling interface is located at the first and second circuit emergency water supply interfaces. The reliability data of mobile equipment is the fitting value of the power plant's historical data and the equipment's general data. Personnel reliability should at least consider connection and startup errors. The CBDTM method is selected in the cognitive stage, and the THERP method is selected in the execution stage. SPRA-H is used for comprehensive time series analysis, and personnel tension is always high.

[0033] In step 2, the ratio of multiple unit models of the plant-level MUPSA is based on the actual situation of the nuclear power base, ensuring that the units of the same reactor type are in the same model, the upper limit of the ratio of the number of MUPSA model units for a single-stack arrangement is 4, and the upper limit of the ratio of the number of MUPSA model units for a dual-stack arrangement is 2.

[0034] In step 3, the sensitivity calculation examples for independent analysis are set to correspond to the number of different types of mobile equipment from 0 to N, where N is the number of units in the nuclear power base. A sensitivity calculation example for combined analysis should also be set. To reduce the computational complexity, the sensitivity calculation example for combined analysis can be set based on the preliminary configuration scheme in step 4 and the existing configuration scheme of the nuclear power base.

[0035] In step 4, the risk change assessment consists of two parts: a forward validation method for risk analysis and a reverse validation method for risk analysis. The purpose of the forward validation is to analyze the number of additional mobile equipment that will yield the greatest risk improvement, assuming additional mobile equipment is required. The purpose of the reverse validation is to analyze whether the current situation warrants an increase to the required number of additional equipment, given the forward validation number. The forward validation method for risk analysis and assessment has three analytical elements: single-unit CDF deterioration improvement analysis, multi-unit CDF baseline improvement analysis, and comprehensive probability confidence improvement analysis. The reverse validation method for risk analysis and assessment draws heavily on the "Probabilistic Risk Assessment for Risk-Guided Decision-Making Methods for Changes to the License Basis of a Specific Power Plant" (NNSA-0147), published by the National Nuclear Safety Administration. This method determines whether the risk associated with a nuclear power base change is acceptable by calculating the CDF increment introduced by the change. Similarly, in the present invention, this method can be used to determine whether the existing mobile equipment configuration meets the change requirements. Specifically, if the configuration recommended in the forward validation analysis is reduced to the existing configuration, is the risk acceptable? If the ΔCDF is less than 10E-6 / reactor-year, the change is considered acceptable. The number of configurations in the recommended configuration is reduced, and the calculation continues until the existing configuration is acceptable. If the ΔCDF is greater than 10E-6 / reactor-year, the change is considered unacceptable, and the calculation is terminated, with the current configuration being the minimum configuration with acceptable risk. The solution selected through forward and directional validation analysis is considered the preliminary configuration solution.

[0036] In step 5, a four-objective optimization model is established, which includes minimizing the risk criterion (MUCDF / MULERF), minimizing the configuration maintenance cost, maximizing the availability, and maximizing the available time for emergency dispatch. The NSGA-II algorithm is used to take the Pareto optimal solution as the comprehensive optimization analysis plan, and the intersection of the Pareto optimal solution and the preliminary configuration plan is taken as the final configuration recommendation in step 6.

[0037] Example 1:

[0038] A nuclear power base has six units, of which units 1-4 are single-stack Type A units, and units 5-6 are dual-stack Type B units. The base is equipped with one medium-pressure mobile emergency diesel generator and four mobile emergency water pumps. This configuration was analyzed and evaluated using the method described in this invention.

[0039] Steps 1 to 3 are carried out according to the specific conditions of the nuclear power base.

[0040] Step 4: Use the calculation results to analyze risk changes and preliminarily select a configuration plan.

[0041] ...In order to analyze the impact of mobile equipment with different configurations on the comprehensive risk of the nuclear power base, two types of risk analysis methods were adopted, namely the forward verification method of risk analysis and evaluation and the reverse verification method of risk analysis and evaluation.

[0042] The analysis benchmark for the CDF deterioration improvement analysis of a single unit is the MUCDF of the simple calculation combination of the SUCDF of each unit. SU The difference between this value and the MUCDF calculated from the multi-unit model can be considered the relative risk deterioration of the multi-unit model compared to a single unit. This deterioration can be understood as assuming that the single-unit state is the safest state for the entire plant. The multi-unit state introduces an incremental risk, which is the relative risk deterioration of the multi-unit model compared to a single unit. Adding mobile equipment reduces this incremental risk. This reduction is the deterioration improvement value, and its ratio to the original risk deterioration is the deterioration improvement rate.

[0043] Among them, there are:

[0044] MUCDF SU =MUCDF SU1-4 ×(1-MUCDF SU5-6 )+MUCDF SU5-6 ×(1-MUCD SU1-4 )+SUCDF 1-4 ×SUCDF 5-6

[0045] Among them, SUCDF 1-4 It is the sum of CD calculation values of units 1-4 of the nuclear power base. 5-6 It is the sum of the CD calculation values of units 5 and 6 of the nuclear power base.

[0046] Among them, there are:

[0047] MUCDF SU1-4 =((SUCDF 1-4 ) 2 ×(1-SUCDF 1-4 ) 2 )×6+((SUCDF 1-4 ) 3 ×(1-SUCDF 1-4 ) 1 )×4+(SUCDF 1-4 ) 4

[0048] MUCDF SU5-6 =(SUCDF 5-6 ) 2

[0049] The analytical benchmark for the multi-unit CDF baseline improvement analysis is the MUCDF without any mobile equipment added. This calculated value is directly calculated using the multi-unit model and represents the combined probability of two or more units experiencing CD failures throughout the plant, assuming no mobile equipment is involved and a severe external event causes all units to experience a severe external event-induced initiating event simultaneously. When mobile equipment is added, the MUCDF value is bound to decrease. The difference in decrease is the baseline improvement value, and its ratio to the original baseline MUCDF is the baseline improvement rate. The MUCDF value is directly calculated using RS software, and the consequence analysis of various CD combinations is obtained through MCS post-processing.

[0050] The comprehensive probability confidence improvement analysis is carried out on the basis of the multi-unit CDF benchmark improvement analysis. The probability of CD occurring in units with different numbers is obtained through benchmark calculation. By fitting these probability values with the normal probability distribution, the normal probability distribution diagram of the number of CD units in the multi-unit case is obtained. The probability values corresponding to the 95.45% (±2σ) and 68.27% (±1σ) confidence interval boundaries are obtained by calculating the corresponding standard deviations.

[0051] Next, we calculated the CDF values for CD events occurring in different numbers of units when adding different numbers of mobile equipment. The introduction of mobile equipment causes the CDF value to decrease, and the corresponding horizontal axis (the number of units experiencing CD) moves outside the confidence interval boundaries. When it moves outside a certain confidence interval boundary, it is considered that under this scenario (i.e., the prior scenario of CD events in N units), even if the corresponding number of mobile equipment in the calculation example is added, this scenario is extremely unlikely to occur. ...

[0052] Step 5: Conduct a multi-objective comprehensive optimization analysis based on factors such as configuration maintenance cost, availability, and comprehensive emergency dispatch to further screen configuration solutions.

[0053] ...A three-objective NSGA-II multi-objective optimization genetic algorithm was established using MATLAB. The risk criterion (MUCDF / MULERF) was taken from the set of solutions obtained in step 4, the configuration and maintenance cost was taken as the linear value of the set of solutions obtained in step 4, and the availability was taken as the time after the common cause was triggered in MUPSA. Comprehensive emergency dispatch was not considered in this example. ...

[0054] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A nuclear power base mobile equipment configuration evaluation method based on multi-unit safety evaluation is characterized by: The following steps are involved: Step 1: Model the mobile equipment and use PSA software to add the mobile equipment to the event tree and fault tree of the single-unit PSA model. Analyze the time of mobile equipment intervention and personnel reliability events. In step 1, the models for mobile equipment that need to be modeled include a first-level internal event PSA model, a first-level external event PSA model, a second-level PSA model, and a spent pool PSA model. The specific modeling interfaces are based on the reactor type and power plant modification items. For mobile emergency diesel generators, the modeling interface is located after the unit's emergency diesel generator fails. For mobile water supply pumps, the modeling interface is located at the primary and secondary circuit emergency water supply interfaces. The reliability data of the mobile equipment is the fitted value of the power plant's historical data and the equipment's general data. The CBDTM method is selected in the cognitive stage, and the THERP method is selected in the execution stage. SPRA-H is used for comprehensive time series analysis, and personnel tension is always high. Step 2: Use PSA software to establish the MUPSA model; Step 3: Set up a sensitivity analysis case and perform calculations; Step 4: Use the calculation results to analyze risk changes and preliminarily select a configuration plan; Step 5: Conduct a multi-objective comprehensive optimization analysis based on configuration maintenance costs, availability, and comprehensive emergency dispatch to further screen configuration solutions. Step 6: Provide an evaluation of the existing configuration of the nuclear power base and configuration recommendations based on the selected configuration options.

2. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 1, characterized in that: In step 2, the ratio of multiple unit models of the plant-level MUPSA is based on the actual situation of the nuclear power base, ensuring that the units of the same reactor type are in the same model, the upper limit of the ratio of the number of MUPSA model units for a single-stack arrangement is 4, and the upper limit of the ratio of the number of MUPSA model units for a dual-stack arrangement is 2.

3. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 1, characterized in that: In step 3, the setting of the sensitivity calculation examples of independent analysis corresponds to the number of different types of mobile equipment from 0 to N, where N is the number of units in the nuclear power base, and the sensitivity calculation examples of combined analysis are set. In order to reduce the amount of calculation, the sensitivity calculation examples of the combined analysis are set based on the existing configuration plan of the nuclear power base.

4. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 1, wherein: In step 4, the risk change assessment consists of two parts: a forward verification method of the risk analysis and assessment and a reverse verification method of the risk analysis and assessment.

5. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 4, characterized in that: The forward verification method assumes that additional mobile devices are to be added, and analyzes how many additional mobile devices will bring about greater risk improvement benefits.

6. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 4, characterized in that: The reverse verification method analyzes whether it is necessary to increase the additional number under the premise of obtaining the additional number of forward verification.

7. The method for evaluating mobile equipment configuration in a nuclear power base based on multi-unit safety evaluation according to claim 1, characterized in that: In step 5, a four-objective optimization model is established, namely, minimizing risk criteria, minimizing configuration and maintenance costs, maximizing availability, and maximizing available time for emergency dispatch. The NSGA-II algorithm is used to take the Pareto optimal solution as the comprehensive optimization analysis plan, and the intersection of the Pareto optimal solution and the preliminary configuration plan is taken as the final configuration recommendation in step 6.

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