A three-level probabilistic safety assessment method and system for nuclear power plants

Abstract

The present invention relates to a three-level probabilistic safety assessment method and system for a nuclear power plant. The method processes the probabilistic source terms given by the second-level probabilistic safety assessment through interfaces such as nuclide grouping conversion and release period simplification to obtain source terms suitable for the three-level probabilistic safety assessment. On this basis, the hourly meteorological data of the nuclear power plant throughout the year are sampled and analyzed, and combined with basic data such as population, diet, and land use around the plant site, the public exposure dose and health risk at different distances from the release source of the nuclear power plant are simulated. The present invention can be directly applied to the dose consequence analysis and public health risk assessment after a nuclear power plant accident, and provides a set of standardized work processes and analysis methods for the implementation of the three-level probabilistic safety assessment of nuclear power plants.

Description

Technical Field

[0001] The present invention belongs to the field of probabilistic safety assessment of nuclear power plants, and in particular relates to a three-level probabilistic safety assessment method and system for nuclear power plants. Background Art

[0002] Probabilistic safety assessment (PSA) is a technical method used to identify potential accidents that may occur in the operation of complex engineering systems, estimate their probability of occurrence, and determine their possible consequences. In the system safety analysis of nuclear power plants, probabilistic safety assessment strongly supports the management decision of safety risks during the design, manufacture, use and maintenance of the system, and ensures the safe operation of nuclear power plants.

[0003] The probabilistic safety assessment (PSA) of nuclear power plants is mainly divided into three levels. Level 1, core damage analysis: using the probability method of event tree and fault tree to analyze the design and operation, and derive the accident sequence and its frequency of occurrence that lead to core melting; Level 2, source term analysis, based on the level 1 analysis, analyzes the physical process of the accident and the behavior of the containment, and calculates the radioactive source terms of different accident release types; Level 3, consequence evaluation: evaluate the characteristics of released radioactive materials, the degree of atmospheric diffusion and the dose.

[0004] At present, the research on the first and second level probabilistic safety assessment of nuclear power plants at home and abroad is relatively mature, but there is still a lack of a standardized workflow and framework for the third level probabilistic safety assessment of nuclear power plants. The third level probabilistic safety assessment of nuclear power plants is based on the source term proposed in the second level probabilistic safety assessment. By simulating the diffusion and migration of radioactive substances to the environment, combined with the population, meteorology, diet, land use and other characteristics of the nuclear power plant, the accident consequence assessment program is used to simulate the exposure dose and health risks of the public at different distances from the nuclear power plant. Since the release of radioactive substances to the environment after the accident is mainly through the atmospheric release route, the release to water bodies can be basically ignored. The present invention only involves the consequence assessment of the release of radioactive substances through the atmospheric release route, and does not include the consequence assessment of the release to water bodies. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system suitable for the three-level probabilistic safety assessment of nuclear power plants, which can be directly used for the radiation consequence analysis of nuclear power plants and the public health risk assessment.

[0006] The technical solution of the present invention is as follows: A three-level probabilistic safety assessment method for a nuclear power plant, comprising:

[0007] (1) Process the probabilistic source terms given by the second-level probabilistic safety assessment of nuclear power plants to form source terms suitable for the third-level probabilistic safety assessment of nuclear power plants;

[0008] (2) Based on the processed probabilistic safety assessment source terms, the diffusion and migration process of radioactive substances in the atmosphere is simulated through a reasonable meteorological sampling method, and the concentration of radioactive substances deposited on the ground after dry and wet deposition processes is given;

[0009] (3) Simulate the exposure doses to the public at different time periods and at different distances from the release source of the nuclear power plant under different exposure pathways;

[0010] (4) Based on the ground deposition concentration of radioactive materials and combined with the diet and land use data around the nuclear power plant, simulate the activity concentration of key radionuclides in different food categories in the long term after the accident;

[0011] (5) Based on the exposure dose to the public obtained in step (3), combined with the health effect model, simulate the possible health risks to the public in the long term after the accident.

[0012] Furthermore, in the third-level probabilistic safety assessment method for a nuclear power plant as described above, in step (1), the probabilistic source terms given by the second-level probabilistic safety assessment of the nuclear power plant are simplified and processed into a finite number of release time periods, and the probabilistic source terms are processed into a nuclide grouping form of the third-level probabilistic safety assessment calculation program.

[0013] Furthermore, in the three-level probabilistic safety assessment method for nuclear power plants as described above, the reasonable meteorological sampling method described in step (2) is to sample the meteorological conditions at the same distance from the release source of the nuclear power plant at fixed time periods throughout the year.

[0014] Furthermore, in step (2), the concentration of radioactive substances deposited on the ground after dry and wet deposition processes under 50% meteorological probability level conditions is given.

[0015] Furthermore, in the three-level probabilistic safety assessment method for nuclear power plants as described above, the different exposure pathways described in step (3) include air immersion external exposure, inhalation internal exposure, and surface deposition external exposure; and the public exposure dose includes effective dose and organ dose.

[0016] Furthermore, in the three-level probabilistic safety assessment method for nuclear power plants as described above, the key nuclides described in step (4) include I-131 and Cs-137; and the longer-term post-accident phase is one year after the accident.

[0017] Furthermore, in the three-level probabilistic safety assessment method for nuclear power plants as described above, the health risks described in step (5) include the risks of acute mortality, acute disease, late disease, and cancer death.

[0018] A three-level probabilistic safety assessment system for a nuclear power plant, comprising:

[0019] The secondary and tertiary probabilistic safety assessment interface module is used to process the probabilistic source terms given by the secondary probabilistic safety assessment of nuclear power plants to form source terms suitable for the tertiary probabilistic safety assessment of nuclear power plants;

[0020] The atmospheric diffusion simulation module is used to simulate the diffusion and migration process of radioactive substances in the atmosphere based on the processed probabilistic safety assessment source items through reasonable meteorological sampling methods, and give the concentration of radioactive substances settled on the ground after dry and wet deposition processes;

[0021] The dose calculation module is used to simulate and calculate the exposure doses received by the public at different time periods and at different distances from the release source of the nuclear power plant under different exposure pathways after the accident;

[0022] The food chain calculation module is used to simulate the activity concentration of key nuclides in different food categories in the long term after the accident based on the ground deposition concentration of radioactive materials combined with the diet and land use data around the nuclear power plant;

[0023] The risk analysis module is used to simulate the possible health risks to the public in the long term after the accident based on the exposure dose to the public and the health effect model.

[0024] The beneficial effects of the present invention are as follows: The present invention proposes for the first time an analysis method applicable to the third-level probabilistic safety assessment of nuclear power plants, using the probabilistic source terms given by the second-level probabilistic safety assessment, and after interface processing such as nuclide grouping conversion and release period simplification, the source terms required for the third-level probabilistic safety assessment are given. On this basis, a sampling analysis of the hourly meteorological data of the nuclear power plant throughout the year is carried out, and combined with basic data such as population, diet, and land use around the plant site, the accident consequence assessment program is used to simulate the public exposure dose and health risks at different distances from the release source of the nuclear power plant. The present invention can be directly applied to the dose consequence analysis and public health risk assessment after nuclear power plant accidents, and provides a set of standardized work processes and analysis methods for the implementation of the third-level probabilistic safety assessment of nuclear power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the three-level probabilistic safety assessment process for a nuclear power plant provided by the present invention;

[0026] Figure 2 It is a schematic diagram of the secondary and tertiary probabilistic safety assessment interface flow in a specific embodiment of the present invention;

[0027] Figure 3 It is a schematic diagram of the source item format given in the secondary probabilistic safety assessment in a specific embodiment of the present invention;

[0028] Figure 4 This is a simplified schematic diagram of the release time period processing in a specific embodiment of the present invention;

[0029] Figure 5 It is a schematic diagram of the source item format suitable for level 3 probabilistic safety assessment after interface processing in a specific embodiment of the present invention;

[0030] Figure 6 It is a schematic diagram of the exposure dose to the public in a specific embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the activity concentration of food in a specific embodiment of the present invention;

[0032] Figure 8 It is a schematic diagram of public health risks in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] The present invention provides an analysis method suitable for the third-level probabilistic safety assessment of nuclear power plants. Figure 1 The process of three-level probabilistic safety assessment of nuclear power plants is given, including the following steps:

[0035] (1) The probabilistic source terms given by the secondary probabilistic safety assessment of the nuclear power plant are parsed through the interface module, and the sequence of source term release shares given by the probabilistic source terms that change with time is simplified and processed into a finite number of release periods; according to the different nuclide groupings of the secondary probabilistic safety assessment calculation program and the tertiary probabilistic safety assessment calculation program, the probabilistic source terms are processed into the nuclide grouping form of the tertiary probabilistic safety assessment calculation program. Since the secondary probabilistic safety assessment calculation program and the tertiary probabilistic safety assessment calculation program have different considerations for the properties of nuclides during calculation, there are also some differences in the grouping form. The secondary probabilistic safety assessment calculation program pays more attention to the volatility of the substance, and calculates the concentration of the substance at different locations based on the volatility, so the substances are generally grouped according to the compound; the tertiary probabilistic safety assessment calculation program often pays more attention to the ionization effect of the nuclide, so the concentration of each nuclide is obtained. For example, in the second-level probabilistic safety assessment calculation program, the concentrations of CsI and CsOH are generally calculated. In the third-level probabilistic safety assessment calculation program, it is necessary to know the concentrations of Cs isotopes such as Cs-134, Cs-137 and I isotopes such as I-131, I-132.

[0036] Figure 2 The interface flow chart from level 2 probabilistic safety assessment to level 3 probabilistic safety assessment is given.

[0037] Figure 2 middle:

[0038] MFPACT(J): initial core mass of nuclide J (kg);

[0039] MFPIN(K): initial core mass of element K (kg);

[0040] MFPO(I): initial core mass of all elements grouped as I (kg);

[0041] NFPACT(J): amount of initial substance of nuclide J (mol);

[0042] NFPIN(K): the amount of initial substance of element K (mol);

[0043] MTFPO(I): the amount of initial substances of all elements grouped as I (mol);

[0044] MOLFPE(I): total molar mass of all elements grouped as I (kg / mol);

[0045] FAFPO(M): the share of element M in group I;

[0046] FNUCLD(J): the fraction of nuclide J in element I;

[0047] MFP(I): mass of nuclide I in the core that changes with the progress of the accident (kg);

[0048] NTFP(I): the amount of substances of all elements grouped as I in the core that change with the progress of the accident (mol);

[0049] NFPE(I): the amount of substance of element K in the core that changes with the progress of the accident (mol);

[0050] NFPNC(J): the amount of nuclide J in the core that changes with the progress of the accident (mol);

[0051] FP: fission products.

[0052] (2) Based on the probabilistic safety assessment source items obtained after processing, combined with the hourly meteorological data of the nuclear power plant throughout the year, through a reasonable meteorological sampling method, the atmospheric diffusion simulation module of the accident consequence assessment program is used to simulate the diffusion and migration process of radioactive substances in the atmosphere using a known method, and the concentration of radioactive substances deposited on the ground after dry and wet deposition processes under different meteorological probability levels is given.

[0053] (3) Using the dose calculation module of the accident consequence assessment program, the publicly known methods are used to simulate and calculate the exposure doses to the public at different time periods and at different distances from the release source of the nuclear power plant under different exposure pathways (air immersion external exposure, inhalation internal exposure, and surface deposition external exposure).

[0054] (4) Based on the ground deposition concentration of radioactive materials, combined with the diet, land use and other data around the nuclear power plant, the food chain calculation module of the accident consequence assessment program is used to simulate the activity concentration of key nuclides in different food categories in the long term after the accident (such as 1 year after the accident) using publicly known methods.

[0055] (5) Combined with the public exposure dose and relevant parameters of the health effect model (including the activity concentration of key radionuclides in different food categories), the risk analysis module of the accident consequence assessment program is used to simulate the possible risks of acute mortality, acute illness, late illness and cancer death to the public in the long term after the accident.

[0056] Example

[0057] This embodiment provides a specific process of a three-level probabilistic safety assessment method for a nuclear power plant, including the following steps:

[0058] (1) First, the secondary probabilistic safety assessment source items of nuclear power plants are processed. The secondary probabilistic safety assessment of nuclear power plants will classify all accidents of nuclear power plants into about 10 release categories according to the type of containment release, and process the source items of each release category into source items suitable for the third-level probabilistic safety assessment. Taking the RC04 release category of the secondary probabilistic safety assessment source item of nuclear power plants as an example, the sequence of the change of release share over time is shown as follows: Figure 3 As shown, firstly, through the processing and analysis of the interface module, the source items suitable for the third-level probabilistic safety assessment are given. Figure 4 A simplified treatment of the release time period is given, with the horizontal axis representing the time after the accident started and the vertical axis representing the release share. Figure 4 The middle line segment is the release share curve calculated by the secondary probabilistic safety assessment calculation program, and the black dots are the release share curves after simplification. It can be seen that the simulation points in the figure are highly consistent with the continuous curve. Figure 5 The processing results after nuclide grouping conversion are given.

[0059] (2) Based on the source items after the above processing, samples are taken at the same distance from the release source of the nuclear power plant and the hourly meteorological conditions throughout the year, with sampling every 6 hours. The diffusion and migration process of radioactive substances in the atmosphere is simulated by the accident consequence assessment program, and the concentration of radioactive substances deposited on the ground after dry and wet deposition processes under the 50% meteorological probability level conditions is given.

[0060] (3) Then calculate the effective dose and organ dose to the public within a radius of 5 km from the nuclear power plant release source within 2 days or 7 days through air immersion external exposure, inhalation internal exposure, surface deposition external exposure and other pathways. For an example of a 7-day effective dose, see Figure 6 shown.

[0061] (4) Based on the concentration of radioactive substances deposited on the ground after dry and wet deposition processes under the 50% meteorological probability level given in step (2), combined with the diet, land use and other data around the nuclear power plant, and using the food chain calculation module of the accident consequence assessment program, simulate the activity concentration of key radionuclides such as I-131 and Cs-137 in food categories such as grains, leafy vegetables, and meat one year after the accident. An exemplary mass concentration of Cs-137 in grains is shown in Figure 7 shown.

[0062] (5) Based on the effective dose and organ dose calculated in step (3), combined with the health effect model, the risk analysis module of the accident consequence assessment program is used to simulate the possible acute mortality, acute morbidity, late morbidity and cancer mortality risks to the public in the long term after the accident. An exemplary late leukemia treatment rate is shown in Figure 8 shown.

[0063] It will be apparent to those skilled in the art that the structure of 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-restrictive 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.

[0064] 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 three-level probabilistic safety assessment method for a nuclear power plant, comprising the following steps: (1) Simplify the probabilistic source terms given by the second-level probabilistic safety assessment of nuclear power plants, simplify the sequence of source term release shares given by the probabilistic source terms over time, process them into a finite number of release periods, and process the probabilistic source terms into the nuclide grouping form of the third-level probabilistic safety assessment calculation program to form source terms suitable for the third-level probabilistic safety assessment of nuclear power plants; (2) Based on the processed probabilistic safety assessment source items, the diffusion and migration process of radioactive substances in the atmosphere is simulated through a reasonable meteorological sampling method to provide the concentration of radioactive substances deposited on the ground after the dry and wet deposition processes; the reasonable meteorological sampling method is to sample at fixed time periods at the same distance from the nuclear power plant release source and under hourly meteorological conditions throughout the year; (3) Simulate the exposure doses to the public at different time periods and at different distances from the release source of the nuclear power plant under different exposure pathways; (4) Based on the ground deposition concentration of radioactive materials and combined with the diet and land use data around the nuclear power plant, simulate the activity concentration of key radionuclides in different food categories in the long term after the accident; (5) Based on the exposure dose to the public obtained in step (3), combined with the health effect model, simulate the possible health risks to the public in the long term after the accident.

2. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1, characterized in that: In step (2), the concentration of radioactive substances deposited on the ground after dry and wet deposition processes under 50% meteorological probability level conditions is given.

3. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1, characterized in that: The different irradiation pathways described in step (3) include air immersion external irradiation, inhalation internal irradiation, and surface deposition external irradiation.

4. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1 or 3, characterized in that: The public exposure dose mentioned in step (3) includes the effective dose and the organ dose.

5. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1, characterized in that: The key nuclides described in step (4) include I-131 and Cs-137.

6. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1 or 5, characterized in that: The longer term post-accident period described in step (4) is one year after the accident.

7. The three-level probabilistic safety assessment method for a nuclear power plant according to claim 1, characterized in that: The health risks described in step (5) include the risks of acute mortality, acute illness, late illness and cancer death.

8. A three-level probabilistic safety assessment system for a nuclear power plant, comprising: The second-level and third-level probabilistic safety assessment interface modules are used to simplify the probabilistic source terms given by the second-level probabilistic safety assessment of the nuclear power plant, simplify the sequence of source term release shares given by the probabilistic source terms over time, process them into a finite number of release periods, and process the probabilistic source terms into a nuclide grouping form of the third-level probabilistic safety assessment calculation program to form source terms suitable for the third-level probabilistic safety assessment of the nuclear power plant; The atmospheric diffusion simulation module is used to simulate the diffusion and migration process of radioactive substances in the atmosphere based on the processed probabilistic safety assessment source items through a reasonable meteorological sampling method, and give the concentration of radioactive substances settled on the ground after the dry and wet deposition process; the reasonable meteorological sampling method is to sample at fixed time periods at the same distance from the release source of the nuclear power plant and under hourly meteorological conditions throughout the year; The dose calculation module is used to simulate and calculate the exposure doses received by the public at different time periods and at different distances from the release source of the nuclear power plant under different exposure pathways after the accident; The food chain calculation module is used to simulate the activity concentration of key nuclides in different food categories in the long term after the accident based on the ground deposition concentration of radioactive materials combined with the diet and land use data around the nuclear power plant; The risk analysis module is used to simulate the possible health risks to the public in the long term after the accident based on the exposure dose to the public and the health effect model.

Images