A method for analysis of radioactive source terms for nuclear power plant accidents

Abstract

The application relates to a radioactive source item analysis method for nuclear power plant accidents, and belongs to the field of nuclear radiation safety. The application provides a source item share calculation method based on ORIGEN. The source item share calculated by the method can consider the source item decay law at different moments, is suitable for source item nuclide share calculation of different positions, and can be used for solving the quantity value of each moment of radioactive nuclides changing with time. The application has important significance and role for improving the accuracy of radiation safety analysis of a nuclear reactor.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of for nuclear power plant accident radioactive source term analysis method, belong to nuclear radiation safety field. BACKGROUND

[0002] The current use of nuclear energy needs to be assisted by extremely high safety measures, when nuclear accident occurs, if mishandling will cause incalculable consequences.For the analysis of accident source term is the most critical link in the whole nuclear accident disposal process, through the calculation and analysis of system program, the release amount of radioactive source term in nuclear accident state can be estimated, according to the source term calculation result, the radiation dose rate of personnel in different positions in nuclear device site is estimated, so as to achieve the purpose of quickly formulating rescue plan.

[0003] MELCOR / MAAP and other programs for severe reactor accident simulation divide radionuclides into several groups, each group represents the sum of a certain type of nuclide, and cannot specifically give the radioactivity value of a certain nuclide under each type, which brings difficulties to radiation consequence evaluation, and needs to multiply a certain type of radionuclide by the radioactivity proportion of the specific nuclide under the type, so as to calculate the radioactivity value of the specific nuclide.

[0004] The method commonly used at home and abroad at present is to refer to the proportion of each nuclide in containment given in the standard NUREG1465 of the United States, which is derived from the containment experiment of a specific power plant reactor, and is only applicable to the calculation of radioactive nuclides in the containment of power plant reactor. If the proportion of the standard is directly used to calculate the radioactivity of the primary system, plant building and other parts and the reactor compartment of ship reactor, it lacks basis and even leads to large error. In order to solve this technical problem, a source term proportion calculation method based on ORIGEN is proposed in this paper. The source term proportion calculated by this method can consider the decay law of source term at different times, and is applicable to the source term nuclide proportion calculation of different parts. Using the source term proportion, the value of radioactive nuclide at each time can be solved. This method has important significance and role for improving the accuracy of radiation safety analysis of nuclear reactor. SUMMARY

[0005] The present application provides a kind of for nuclear power plant accident radioactive source term analysis method to solve the problems existing in the prior art, the present application can consider the decay law of source term at different times, and is applicable to the source term nuclide proportion calculation of different parts, improves the accuracy of radiation safety analysis of nuclear reactor.

[0006] To achieve the above object, the technical scheme provided by the present application is as follows: a kind of for nuclear power plant accident radioactive source term analysis method, according to the following steps is operated:

[0007] (1) Initialization of ORIGEN program: first, according to the decay period law of radionuclides, the decay table after shutdown is set, and the operation history of the reactor and the decay table after shutdown are taken as the initial conditions to initialize the ORIGEN program, which provides the basis for the calculation of the value of each radionuclide in each category;

[0008] (2) Calculation of radioactive fraction based on decay table: the ORIGEN program, i.e. the burnup calculation program, is used to calculate the radioactive value of the nuclide under the decay table time sequence mentioned above; and for the concerned radionuclide category, the total amount of each radionuclide is first calculated, and then the fraction of each radionuclide in each category is calculated;

[0009] (3) Interpolation operation of radionuclide fraction: at a certain time, the calculated radionuclide fraction is interpolated according to time to obtain the interpolated radionuclide fraction at any time, and the values before and after the interval are selected;

[0010] (4) Calculation of total amount of each category of radionuclide in the containment and other parts: based on the total amount of each category of radionuclide calculated in step (2), the severe accident analysis program MELCOR is initialized, and the total amount of each category of radionuclide in the containment and other parts is calculated by using the MELCOR program;

[0011] (5) Solution of radionuclide value: through the above steps (1) to (3), the radionuclide decay fraction based on ORIGEN is obtained, combined with the total amount of each category of radionuclide calculated by the severe accident analysis program MELCOR in step (4), and multiplied by the above-mentioned radionuclide fraction changing with time, the value of a certain radionuclide at any time in the containment and other parts considering the decay effect can be obtained.

[0012] The decay time table setting rule in step (1) is as follows: because there are many nuclides with short half-life at the initial stage of shutdown, the decay time within 1 hour after shutdown should be as detailed as possible, and after 1 hour, the decay is considered once per hour, and the total decay time can be set according to the requirements. This method takes 72.0 hours after shutdown as an example for introduction. According to the above requirements, the decay table proposed by this method is 0.0s, 0.1s, 1.0s, 10.0s, 100.0s, 300.0s, 600.0s, 1800.0s, 1.0h, 2.0h, 3.0h……, 72.0h.

[0013] In step (2), the radionuclide categories of interest are processed, and 82 nuclides of inert gas category, 74 nuclides of alkali metal category and 56 nuclides of halogen category are classified according to the radionuclide categories frequently concerned in radionuclide calculation.

[0014] In step (3), the interpolation operation is performed on the selected time value x, A≥x≥B, wherein A and B are time values corresponding to the calculated radionuclide share, and the operation formula is as follows:

[0015] Interpolation result = A / 3600 hours + (B / 3600 hours - A / 3600 hours) * (B / 3600 hours - A / 3600 hours) / (x / 3600 hours - A / 3600 hours)

[0016] The radionuclide amount value solving method in step (5) is suitable for decay of any part, such as a containment, at any time.

[0017] According to the above technical solution, the radionuclide source term analysis method for nuclear power plant accidents provided by the present application is based on the ORIGEN source term share calculation method, considers the decay law of the source term at different times, is suitable for source term nuclide share calculation of different parts, and uses the source term share to solve the amount value of the radionuclide at each time varying with time. The present application has the following advantages compared with the prior art:

[0018] The present application solves the technical problem that the MELCOR program cannot accurately and reasonably calculate the amount value of each radionuclide by calculating the radioactivity share according to the decay law and solving the radionuclide amount value through interpolation operation of the radionuclide share, thereby improving the accuracy of the radiation safety analysis of the nuclear reactor. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Flowchart for calculating the amount value of the radionuclide at the part, such as a containment;

[0020] Figure 2 Example diagram for calculating the difference in radioactivity. DETAILED DESCRIPTION

[0021] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present application is not limited to the following embodiments.

[0022] In one of the technical solutions provided by the present application, a radionuclide source term analysis method for nuclear power plant accidents is shown in the following steps: Figure 1 As shown in the following steps:

[0023] (1) Initialize the ORIGEN program: first, according to the decay period law of the radionuclide, set the decay time table after shutdown, and use the operation history of the reactor and the decay table after shutdown as the initial conditions to initialize the ORIGEN program, thereby providing a basis for calculating the amount value of each major category of nuclide;

[0024] The decay time table setting rule in step (1) is as follows: because there are more nuclides with short half-life in the initial shutdown period, the decay time should be selected as detailed as possible within 1 hour after shutdown, and after 1 hour, the total decay time can be set according to the decay 1 time per hour, and the method takes 72.0 hours after shutdown as an example for introduction. According to the above requirements, the decay table proposed by the method is 0.0s, 0.1s, 1.0s, 10.0s, 100.0s, 300.0s, 600.0s, 1800.0s, 1.0h, 2.0h, 3.0h……, 72.0h.

[0025] (2) Radioactive fraction calculation based on the decay table: using the ORIGEN program, i.e., the point burning consumption calculation program, to calculate the radioactivity value of the nuclides at the time sequence of the above decay table; and processing the concerned radioactive nuclide categories, first calculating the total amount of each type of radioactive nuclide, and then calculating the fraction of each type of radioactive nuclide;

[0026] In step (2), the concerned radioactive nuclide categories are processed, and the 82 nuclides of the inert gas type, the 74 nuclides of the alkali metal type and the 56 nuclides of the halogen type are classified according to the frequently concerned categories in radioactivity calculation.

[0027] (3) Interpolation operation of radioactive nuclide fraction: at a certain time, the calculated radioactive nuclide fraction is interpolated according to time to obtain the interpolated radioactive nuclide fraction at any time, and the values before and after the interval are selected;

[0028] As shown in Figure 2 , in step (3), in the interpolation operation, the selected time value x is interpolated, A≥x≥B, where A and B are the time values corresponding to the calculated radioactive nuclide fraction, and the operation formula is as follows:

[0029] Interpolation result = A / 3600 hours value + (B / 3600 hours value - A / 3600 hours value) * (B / 3600 hours - A / 3600 hours) / (x / 3600 hours - A / 3600 hours)

[0030] (4) Total amount calculation of each category of radioactive nuclides in the containment and other parts: based on the total amount of each category of radioactive nuclides calculated in step (2), the severe accident analysis program MELCOR is initialized, and the migration and diffusion calculation is carried out by using the MELCOR program to obtain the total amount of each category of radioactive nuclides in the containment and other parts;

[0031] (5) Solution of radionuclide amount: Through the above steps (1) to (3), the ORIGEN-based radionuclide decay fraction is obtained, and combined with the total amount of each class of radionuclide calculated by the severe accident analysis program MELCOR in step (4), multiplied by the above-mentioned radionuclide fraction changing with time, the amount of a certain radionuclide at any time in the containment or any other part considering the decay effect can be obtained.

Claims

1. A method for analysis of radioactive source terms for accidents of nuclear power plants, characterized by The operation is performed according to the following steps: (1) Initialization of ORIGEN program: first, according to the decay period law of radionuclides, the decay table of time sequence after shutdown is set, and the running history of the reactor and the decay table after shutdown are taken as the initial conditions to initialize the ORIGEN program, which provides the basis for the calculation of the value of each radionuclide in each category; (2) Calculation of radioactive fraction based on the decay table: the ORIGEN program, i.e. the burnup calculation program, is used to calculate the radioactive value of the nuclide under the time sequence of the above decay table; and for the concerned radionuclide category, the total amount of each radionuclide is first calculated, and then the fraction of each radionuclide in each category is calculated; (3) Interpolation operation of radionuclide fraction: at a certain time, the calculated radionuclide fraction is interpolated according to time to obtain the interpolated radionuclide fraction at any time, and the values before and after the interval are selected; the selected time value x is interpolated, A≥x≥B, where A and B are the time values corresponding to the calculated radionuclide fraction, and the operation formula is as follows: Interpolation result=A / 3600 hours value+(B / 3600 hours value-A / 3600 hours value)*(B / 3600 hours-A / 3600 hours) / (x / 3600 hours-A / 3600 hours); (4) Calculation of total amount of each category of radionuclide in the containment: based on the total amount of each category of radionuclide calculated in step (2), the severe accident analysis program MELCOR is initialized, and the migration and diffusion calculation is carried out by using the MELCOR program to obtain the total amount of each category of radionuclide in the containment; (5) Solution of radionuclide value: through the above steps (1)-(3), the radionuclide decay fraction based on ORIGEN is obtained, combined with the total amount of each category of radionuclide calculated by the severe accident analysis program MELCOR in step (4), and multiplied by the above radioactive fraction varying with time, the value of a certain radionuclide at any time in any part of the containment considering the decay effect can be obtained.

2. The method for analysis of radioactivity source terms for accidents of nuclear power plants according to claim 1, characterized in that: The decay table in step (1) is set according to the half-life rule of nuclides, and the time interval of decay time is gradually increased within 1 hour after shutdown, and after 1 hour, the decay is considered once per hour, and the total decay time is set according to the demand.

3. The method for analysis of radioactivity source terms for accidents of nuclear power plants according to claim 1, characterized in that: In step (2), the radionuclide categories of interest are processed, and the 82 nuclides of inert gas, 74 nuclides of alkali metal and 56 nuclides of halogen are classified according to the radionuclide categories often concerned in radionuclide calculation.

4. The method for analysis of radioactivity source terms for accidents of nuclear power plants according to claim 1, characterized in that: The solution method of radionuclide value in step (5) is suitable for decay in any part of the containment at any time.

Images