Nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization

Abstract

The invention relates to a nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization, and the method comprises the steps: evaluating the initial value of a variable parameter related to the nuclear facility radiation dose; calculating the total irradiation dose of each typical population influenced by the target nuclear facility under the corresponding irradiation path, and the contribution rate of the irradiation dose of each irradiation path to the total irradiation dose; identifying each irradiation path as a key path or a non-key path according to the contribution rate; screening out nuclides of which the contribution rates to the irradiation doses of different paths reach the standard; variable parameters related to the screened nuclides are used as key parameters; and analyzing the key parameters by adopting an EFAST algorithm to obtain high-sensitivity parameters and medium-sensitivity parameters, carrying out localization correction on the high-sensitivity parameters and the medium-sensitivity parameters, and carrying out dose evaluation again based on localization correction values. According to the invention, the problem of inaccurate evaluation result caused by lack of quantitative support and localized correction of evaluation parameters and parameter values in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radiation dose evaluation, and in particular to a nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization. BACKGROUND

[0002] Nuclear facilities continuously produce and discharge airborne radioactive effluents during operation, which may have radiation effects on the environment and the public. To scientifically evaluate the environmental safety of nuclear facilities in operation, it is necessary to evaluate the harm caused by radionuclides to relevant personnel and accurately quantify the radiation dose received by the public to provide decision-making basis for the safe operation and radiation protection of nuclear facilities. Since the discharge of airborne effluents from nuclear facilities involves multiple radionuclides, these radionuclides may have radiation effects on the human body through various exposure pathways such as air immersion external exposure, surface deposition external exposure, and ingestion internal exposure. There are numerous influencing parameters for radiation dose evaluation, and there are interrelationships between different parameters. Identifying key parameters for dose evaluation and performing sensitivity analysis is of great significance to improve the accuracy and objectivity of dose evaluation.

[0003] The existing dose evaluation methods have the following problems: First, the selection of key parameters for dose evaluation mainly relies on expert experience and judgment, lacks quantitative decision support, and therefore subjective bias may exist in the key influencing parameters.

[0004] Second, the sensitivity analysis of dose evaluation parameters mostly uses local single parameter sensitivity analysis methods, such as a study by some scholars on the sensitivity of 11 transfer parameters (including deposition velocity, vegetable consumption, and respiration rate) of 131 I and 234 U radionuclides. Local single parameter sensitivity analysis cannot effectively analyze the non-linear coupling effects between multiple parameters, especially in the context of high / low sensitivity parameter alternation. Third, the parameters lack local correction, making it difficult to adapt to the dose evaluation needs of different regional environmental characteristics. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization, which solves the problem of inaccurate evaluation results caused by the lack of quantitative support and local correction of evaluation parameters and parameter values in the prior art.

[0006] The technical scheme adopted by the present application is as follows: The present application provides a nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization, comprising the following steps: The parameters involved in the radiation dose assessment are classified according to the obtaining manner, and are classified into parameters related to the migration and diffusion concentration of pollutants, deterministic parameters, and variable parameters; the variable parameters are parameters related to the irradiation path, radionuclides, typical population, and characteristics of the region where the target nuclear facility is located; The CFD method is used to simulate and calculate the concentration distribution of the air-borne effluent discharged by the target nuclear facility, so as to obtain the values of the parameters related to the migration and diffusion concentration of pollutants; Based on the values of the parameters related to the migration and diffusion concentration of pollutants, the values of the deterministic parameters, and the initial values of the variable parameters, the total dose of each typical population affected by the target nuclear facility under the corresponding irradiation path is calculated, and the contribution rate of the irradiation dose of each irradiation path to the total dose is calculated; According to the contribution rate, each irradiation path is identified as a key path or a non-key path; A screening standard is set for the identified path, and radionuclides whose contribution rate of the irradiation dose to the path reaches the screening standard are screened out; The variable parameters related to the screened radionuclides are determined, a matrix related to the path, radionuclides, and variable parameters is obtained, and all the variable parameters in the matrix are taken as key parameters; The EFAST algorithm is used to analyze the key parameters, to obtain sensitivity parameters related to the total dose of each typical population under the corresponding irradiation path, and to distinguish high-sensitivity parameters and medium-sensitivity parameters; The high-sensitivity parameters and the medium-sensitivity parameters are locally corrected, and the initial values are replaced by local correction values; Based on the local correction values, the total dose of each typical population under the corresponding irradiation path is recalculated, and a dose assessment result is obtained.

[0007] As a preferred technical solution: Under each irradiation path, the total dose D of each typical population under the corresponding irradiation path is calculated by the following formula: In the formula, i represents the serial number of the radionuclide, m is the number of radionuclides, D 1i 、 D 2i 、 D 3i 、 D 4i are respectively the irradiation doses of the first i radionuclide through four irradiation paths, i.e., air immersion external irradiation, surface deposition external irradiation, inhalation internal irradiation, and ingestion internal irradiation; R fa residence factor; The irradiation dose of each irradiation pathway is the sum of the irradiation dose of all nuclides under the irradiation pathway.

[0008] Under the air immersion external irradiation, the variable parameters include a residence factor, a building shielding produced dose reduction factor, a plume immersion irradiation dose factor; Under the ground deposition external irradiation, the variable parameters include a residence factor, a resuspension factor, a ground deposition external irradiation dose conversion factor, a deposition time of nuclides on the ground; Under the inhalation internal irradiation, the variable parameters include a residence factor, a breathing rate, a resuspension factor, an inhalation internal irradiation dose conversion factor; Under the ingestion internal irradiation, the variable parameters include an annual intake, a concentration factor, a retention fraction, a translocation factor, a fraction of agricultural products in the ingestion related area, an ingestion internal irradiation dose conversion factor.

[0009] Setting a screening criterion for the identified pathway, and screening out nuclides with a contribution rate of irradiation dose of the pathway reaching the screening criterion, including: For the key pathway, selecting a nuclide with the largest contribution rate of irradiation dose of the pathway as a key nuclide, and selecting a nuclide with a contribution rate of irradiation dose exceeding a first set value, or a contribution to the total irradiation dose of all irradiation pathways exceeding a second set value as a major nuclide; According to the contribution rate of the non-key pathway, further dividing into a major pathway with a larger contribution rate and a minor pathway with a smaller contribution rate; For the major pathway, selecting a nuclide with a contribution rate of irradiation dose of the pathway exceeding a third set value, or a contribution to the total irradiation dose of all irradiation pathways exceeding a fourth set value as a major nuclide; For the minor pathway, according to the specific value of the contribution rate, it is determined whether to perform major nuclide screening.

[0010] Localizing correction is performed on the high sensitivity parameters and the medium sensitivity parameters, including: On-site investigation or on-site experiment is performed in the area where the target nuclear facility is located to obtain a value directly reflecting the actual environmental characteristics; Alternatively, an experience recommended value of an area with similar environmental characteristics to the area where the target nuclear facility is located is selected.

[0011] The parameters related to the concentration of pollutant migration and diffusion include a long-term diffusion factor, a ground deposition concentration, and a ground air concentration value.

[0012] The CFD method is used to simulate and calculate the concentration distribution of the gas-borne effluent discharged by the target nuclear facility, including: Obtain meteorological data of a region where the target nuclear facility is located, which includes combined frequencies of different wind directions, wind speeds and stability, annual average rainfall of different wind directions, and annual average wind speed data of different wind directions; Obtain source term data, which includes annual emission amount and emission rate of air-borne effluent; Centering on a position where a main exhaust pipe of the target nuclear facility is located, a simulation region is set, and concentration field distribution simulation is performed by taking the meteorological data and the source term data as inputs, so that values of parameters related to pollutant migration and diffusion concentration at different distances in a downwind direction are obtained.

[0013] The EFAST algorithm is used to analyze the key parameters, including: The value interval of each key parameter is determined, all key parameters are sampled n times in the value interval, and A parameter samples are obtained, wherein A is the total number of key parameters, that is, the number of each group of parameter samples; The parameter samples are taken as input variables and input into the EFAST algorithm model, and the total dose of each typical population under the corresponding exposure pathway is taken as an output variable; The contribution rate of each key parameter sample to the variance of the output variable is calculated, so as to represent the parameter sensitivity; The sensitivity analysis of the interaction between each key parameter is performed by considering the coupling effect between the key parameters, a global sensitivity index is used to represent, and the sensitivity index value of each key parameter is obtained; According to the sensitivity index value, the key parameters are divided into high-sensitivity parameters, medium-sensitivity parameters and low-sensitivity parameters.

[0014] The typical population includes workers of other industrial enterprises around the target nuclear facility, temporary staff in the target nuclear facility site, residents closest to the target nuclear facility, and security personnel in the target nuclear facility site.

[0015] The deterministic parameters include the decay constant of gamma nuclides.

[0016] The technical solution of the present application can achieve at least part of the following beneficial effects: The present application adopts the analysis path of pathway-nuclide-parameter, screens out the key parameters for dose evaluation, obtains high-sensitivity and medium-sensitivity parameters based on the EFAST multi-parameter global sensitivity grading algorithm, performs local correction on the high-sensitivity and medium-sensitivity parameters, and performs evaluation by using the corrected parameter values, so as to effectively solve the technical defects of strong subjectivity in key parameter screening, unscientific sensitivity grading and insufficient parameter localization in the traditional dose evaluation method, and significantly improve the accuracy and objectivity of the evaluation result of the nuclear facility radiation dose.

[0017] The present application classifies the pathways based on the preliminary dose estimation results, selects key nuclides and main nuclides according to the criticality and importance of the pathways, and then obtains relevant parameters to be analyzed based on the selected nuclides, thereby greatly reducing the noise of parameter selection, and the screened parameters are more suitable for the regional environmental characteristics, and are not dependent on expert subjective opinions and experience, and have strong universality.

[0018] The present application uses the EFAST algorithm to perform global sensitivity analysis of multiple parameters, effectively analyzes the nonlinear coupling effect between multiple parameters compared with local sensitivity analysis, and is more suitable for sensitivity identification in the alternating action scene of high-sensitivity and low-sensitivity parameters.

[0019] The present application uses the method of local correction, which is more suitable for the dose evaluation requirements of different regional environmental characteristics, and improves the objectivity and accuracy of the evaluation results.

[0020] Other features and advantages of the present application will be described in the subsequent description, or will be understood by implementing the present application. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The present application is a flowchart of the method of the embodiment.

[0022] Figure 2 The present application is a flowchart of the method of the embodiment.

[0023] Figure 3 The present application is a typical population exposure dose time sequence variation characteristic obtained by the nuclear facility release source item and CFD simulation and dose evaluation in 2016-2020. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application will be described below with reference to the accompanying drawings.

[0025] Reference Figure 1 and Figure 2 The present application is a nuclear facility radiation dose evaluation method based on parameter sensitivity analysis optimization, comprising the following steps: S1. Classify the parameters involved in the radiation dose evaluation according to the obtained method, into parameters related to pollutant migration and diffusion concentration, deterministic parameters, and variable parameters; the variable parameters are related to the irradiation pathway, radionuclide, typical population, and regional characteristics of the target nuclear facility.

[0026] Specifically, for the non-professional typical population, according to the exposure route, exposure time, and the relationship with the location of the nuclear facility, the target nuclear facility exposure typical population is divided into four categories, mainly including: workers of other industrial enterprises around the target nuclear facility, temporary workers in the target nuclear facility site, residents closest to the target nuclear facility, and security personnel in the target nuclear facility site.

[0027] The exposure route of the embodiment mainly includes four kinds: air immersion external exposure, surface deposition external exposure, inhalation internal exposure, and ingestion internal exposure.

[0028] Specifically, the deterministic parameter is a recognized deterministic parameter, such as the decay constant of a gamma nuclide.

[0029] The embodiment mainly performs sensitivity analysis on the variable parameters. After research, the embodiment determines that the variable parameters corresponding to different exposure routes are as follows: Under the air immersion external exposure, the variable parameters include the residence factor, the dose reduction factor caused by building shielding, and the cloud immersion exposure dose factor; Under the surface deposition external exposure, the variable parameters include the residence factor, the resuspension factor, the surface deposition external exposure dose conversion factor, and the deposition time of the nuclide on the ground; Under the inhalation internal exposure, the variable parameters include the residence factor, the resuspension factor, the inhalation internal exposure dose conversion factor, and the resuspension factor; Under the ingestion internal exposure, the variable parameters include the annual intake, the concentration factor, the retention fraction, the translocation factor, the fraction of agricultural products in the area related to ingestion, and the ingestion internal exposure dose conversion factor.

[0030] S2. Screening the variable parameters to obtain key parameters, specifically including: S21. Using the CFD (Computational Fluid Dynamics) method, the concentration distribution of the target nuclear facility gas-borne effluent emission is simulated and calculated to obtain the values of the parameters related to the concentration of pollutant migration and diffusion.

[0031] Specifically, the specific steps of the CFD method include: Obtain the meteorological data of the area where the target nuclear facility is located, which includes the joint frequency of different wind directions, wind speeds, and stability combinations, the annual average rainfall of different wind directions, and the annual average wind speed data of different wind directions; Obtain the source data, including the annual emission amount and emission rate of the gas-borne effluent; A simulation area is set with the target nuclear facility main exhaust cylinder (main radioactive pollutant discharge point) as the center, and the concentration field distribution simulation is performed with the meteorological data and source term data as inputs to obtain the values of the parameters related to the pollutant migration and diffusion concentration at different distances in the downwind direction.

[0032] The parameters related to the pollutant migration and diffusion concentration include a long-term diffusion factor, a ground deposition concentration, and a ground air concentration value.

[0033] S22. Based on the values of the parameters related to the pollutant migration and diffusion concentration, the values of the deterministic parameters, and the initial values of the variable parameters, the total dose of each typical population affected by the target nuclear facility in the corresponding exposure pathway and the contribution rate of the exposure dose of each exposure pathway to the total dose are calculated.

[0034] Specifically, the total dose D of each typical population in the corresponding exposure pathway is calculated by the following formula: In the formula, i represents the serial number of the radionuclide, m is the number of radionuclides, D 1i , D 2i , D 3i , D 4i is the exposure dose of the first i radionuclide through the four exposure pathways of air immersion external exposure, surface deposition external exposure, inhalation internal exposure, and ingestion internal exposure; R f is the residence factor; Specifically, the exposure dose of each exposure pathway is divided by the total dose D to obtain the contribution rate of the exposure dose of each exposure pathway of each typical population to the total dose.

[0035] For radionuclides i , the dose calculation formula of each exposure pathway is as follows: a) Air immersion external exposure dose: (1) In the formula, is the annual whole-body dose of air immersion external exposure, ; is the dose reduction factor caused by building shielding; is the cloud immersion exposure dose conversion factor, ; is the long-term diffusion factor at different distances in the downwind direction, ; is the release rate, .

[0036] b) Surface deposition external exposure dose (2) (3) where, is the annual whole body dose from surface deposition external exposure, ; is the surface radionuclide deposition, ; is the long-term dry deposition factor, ; is the long-term wet deposition factor, ; is the surface deposition external exposure dose conversion factor, ; i is the decay constant of the radionuclide, ; is the effective decay constant, ; is the deposition time of the radionuclide on the ground, .

[0037] Taking into account the dose impact of resuspended radionuclides, the calculation of the cumulative amount of surface radionuclide deposition is performed according to the amount of radionuclides deposited on the ground each year, minus the amount of radionuclides resuspended into the atmospheric environment and the amount of decay, as shown in equation (4): (4) where, C di (n) represents the cumulative amount of radionuclides deposited on the ground per unit area in the n period, Bq / m 2 ; R rei represents the amount of radionuclides resuspended into the atmospheric environment per unit area in the soil, Bq / m 2 , and the calculation formula is as follows: (5) where, K is the resuspension factor of the radionuclide, / m.

[0038] c) Inhaled internal exposure dose (6) R ai = R vi t (7) where, is the annual accumulated effective dose from inhalation, ; is the annual air intake of the individual, ; For inhalation internal exposure dose conversion factor, ;R vi is the breathing rate, m 3 / h; t is the breathing time, h.

[0039] Considering the public inhalation internal exposure caused by the resuspension of the radionuclides deposited on the ground into the atmospheric environment, the inhalation internal exposure dose formula is modified as: (8) d) Ingestion internal exposure dose (9) where, is the annual committed effective dose resulting from the ingestion of contaminated food, ; is the ingestion dose conversion factor, ; is the annual intake of the pth agricultural product, ; is the share of the pth agricultural product produced in the relevant area; is the concentration of the radionuclide in the pth agricultural product, , and the calculation formula is as follows: (10) where, is the specific activity of the radionuclide deposited directly on the agricultural product and transferred to the usable part, , and the influencing parameters include the translocation factor (Tv), the retention share (T), the effective biological mass of the agricultural product at the time of harvest, etc.; is the specific activity of the radionuclide transferred to the agricultural product through the roots, , and the influencing factors include the concentration factor (Bv), the effective surface density of the soil, etc.; is the time from the harvest of the agricultural product to the consumption.

[0040] For a certain radionuclide i , the dose D i it causes is 1i D 2i + D 3i + D 4i (11) For m radionuclides, the dose D (12) Finally, according to the above calculation, the dose D D received by the typical population can be obtained: (13) where, R f is the residence factor, which is the proportion of the residence time of the typical population in the specific contaminated area in the dose assessment.

[0041] Specifically, the irradiation pathways of the typical population can be determined according to the characteristics of typical population activities, living habits, and the like. If there is no certain irradiation pathway, the dose value of the irradiation pathway is 0.

[0042] Specifically, the initial value of the variable parameter is preliminarily determined according to experience and recommended value. Based on the initial value, the preliminary evaluation result of the dose of the typical population can be obtained according to formulas (1)-(13). According to the preliminary evaluation result, the importance of the pathway is identified by the contribution rate calculation.

[0043] S23. According to the contribution rate, each of the irradiation pathways is identified as a key pathway or a non-key pathway.

[0044] Specifically, the dose contribution rate of each irradiation pathway is calculated, which is the ratio of the dose of each pathway to the total dose.

[0045] In this embodiment, the pathway with a dose contribution rate not less than 50% is identified as a key pathway, and the rest is identified as a non-key pathway.

[0046] As a preferred mode, the pathway with a dose contribution rate greater than 25% in the non-key pathway is identified as a main pathway, and the rest is identified as a secondary pathway.

[0047] S24. Setting a screening standard for the identified pathway, and screening out the nuclides with a contribution rate of the irradiation dose of the pathway reaching the screening standard, specifically including: 1) For the key pathway, the nuclide with the largest contribution rate of the irradiation dose of the pathway is selected as a key nuclide, and the nuclide with an irradiation dose contribution rate exceeding a first set value (such as 10%) or an irradiation total dose contribution to all irradiation pathways exceeding a second set value (such as 5%) is selected as a main nuclide; 2) For the main pathway, the nuclide with an irradiation dose contribution rate exceeding a third set value (such as 15%) or an irradiation total dose contribution to all irradiation pathways exceeding a fourth set value (such as 10%) is selected as a main nuclide; 3) For the secondary pathway, whether to perform main nuclide screening is determined according to the specific value of the contribution rate. If the main nuclide screening is performed, the same method as the main pathway can be performed. For the secondary pathway with a low contribution rate value (lower than a preset value), the sensitivity analysis of the pathway related parameters can be considered not to be performed.

[0048] S25. Determining the variable parameters related to the screened nuclides to obtain a matrix about the pathway, the nuclide, and the variable parameter, and taking all the variable parameters in the matrix as key parameters, thereby completing the screening of the key parameters.

[0049] Specifically, the irradiation dose of each irradiation pathway is the sum of the irradiation doses of all the nuclides under the irradiation pathway.

[0050] Specifically, for the screened key pathways, main pathways and secondary pathways, in combination with the nuclides under each irradiation pathway, the key parameters that need to be subjected to sensitivity analysis are screened out, and a “irradiation pathway-nuclide-key parameter” matrix is established, as shown in Table 1.

[0051] Table 1 “irradiation pathway-nuclide-key parameter” matrix

[0052] S3. The EFAST algorithm, i.e. the Extended Fourier Amplitude Sensitivity Test, is used to analyze the key parameters, obtain the sensitivity parameters of the total dose of each typical population under the corresponding irradiation pathway, and distinguish the high sensitivity parameters and the medium sensitivity parameters. Specifically, it includes: The value interval of each key parameter is determined, and all key parameters are sampled n times in the value interval to obtain parameter samples An, wherein A is the total number of key parameters, i.e. the number of each group of parameter samples; The parameter samples are input into the EFAST algorithm model as input variables, and the total dose of each typical population under the corresponding irradiation pathway corresponding to the parameter samples is obtained as the model output; The contribution rate of each key parameter sample to the variance of the model output is calculated to represent the parameter sensitivity; The sensitivity of the interaction between each key parameter is analyzed considering the coupling effect between the key parameters, and a global sensitivity index is used to represent the sensitivity index value of each key parameter; According to the sensitivity index value, the key parameters are divided into high sensitivity parameters, medium sensitivity parameters and low sensitivity parameters.

[0053] The value interval is determined according to experience and actual demand.

[0054] The EFAST algorithm is a mathematical method for global sensitivity analysis, which is a global sensitivity analysis method based on variance decomposition proposed by Saltelli et al. in combination with the advantages of Sobol's method and Fourier amplitude sensitivity test method, considering the coupling effect between parameters, and is suitable for parameter sensitivity analysis of high-dimensional nonlinear models. The parameter sensitivity is represented by calculating the contribution rate of each parameter to the variance of the model result, including the sensitivity of single parameter independent action (first-order sensitivity index) and the sensitivity analysis of the interaction between parameters (global sensitivity index). The calculation process of the EFAST algorithm model is briefly introduced as follows: First, the total variance of the model output is calculated, which can be decomposed into functions of individual parameters and combined parameters: (11) where, V i is the variance of the i-th key parameter i x i , V ij , V ijk and V 12…n is the variance of the interaction of the i-th key parameter with other parameters.

[0055] Then, the contribution rate of each parameter to the variance of the model result is calculated, which represents the parameter sensitivity.

[0056] The direct contribution of the parameter x i to the total variance of the model output can be represented by the first-order sensitivity index S i . The second-order x i , third-order S ij , and high-order sensitivity indices S ijk of the parameter S ij,…,n to the total variance of the model output are calculated as follows: (12) where, S i is the first-order sensitivity index, S ij , S ijk and S ij,…,n are the second-order, third-order, and high-order sensitivity indices, respectively.

[0057] Then, considering the coupling effect between parameters, the sensitivity analysis of the interaction between each parameter is performed, and the global sensitivity index is used to represent it.

[0058] The global sensitivity index S ti takes into account the indirect contribution of the parameter x i to the total variance of the model output due to its interaction with other parameters, and the calculation formula is as follows: (13) According to the above sensitivity indices of each order, the first-order and global sensitivity weights are calculated to obtain the sensitivity index values of each parameter.​

[0059] the first order sensitivity weight of the i-th parameter: i (14) the global sensitivity weight of the i-th parameter: i (15) wherein, w i and W i are the first order sensitivity weight and the global sensitivity weight of the i-th parameter, respectively. i

[0060] Specifically, the parameter sensitivity degree discrimination adopts the grading standard proposed by Knighton et al. When the sensitivity index W≥1, the parameter is a high sensitivity parameter; when 0.2≤W<1, the parameter is a sensitive parameter; when 0.05≤W<0.2, the parameter is a medium sensitivity parameter; and when 0≤W<0.05, the parameter is a low sensitivity parameter.

[0061] S4. Localizing correction is performed on the high sensitivity parameters and the medium sensitivity parameters, and the initial values are replaced by the localizing correction values.

[0062] Through the localizing correction, the parameters can adapt to the dose evaluation requirements of different regional environmental characteristics.

[0063] The preferred way of localizing correction includes: on-site investigation or on-site experiment is performed in the region where the target nuclear facility is located to obtain a value directly reflecting the actual environmental characteristics; or, an experiential recommended value of a region with similar environmental characteristics to the region where the target nuclear facility is located is selected.

[0064] S5. The total dose of each typical population under the corresponding exposure pathway is recalculated (i.e. according to formula (1)-(13)) based on the localizing correction value, and the dose evaluation result is obtained.

[0065] The embodiment can make the parameters used in the dose evaluation of typical populations more suitable for the actual environmental characteristics of the evaluation region, thereby effectively improving the accuracy and reliability of the dose evaluation result of typical populations, and better meeting the dose evaluation requirements in different regional environments.

[0066] The following further illustrates the technical solutions of the present application with a specific target nuclear facility as an experimental example.

[0067] Experimental example: an optimization method for multi-nuclide discharge dose evaluation of a specific target (nuclear facility) site, comprising: (1) determination of typical populations and exposure pathways​​​ Assume that the nuclear facility site exhausts 15 radionuclides, including 234 U, 235 U, 238 U, 3 H, 90 Sr, 137 Cs, 60 Co, 238 Pu, 239 Pu, 240 Pu, 241 Pu, 242 Pu, 241 Am, 85 Kr, and 129 I. The determination of the dose assessment of all radionuclides involves 139 main variable parameters. The annual emissions of each radionuclide from 2016 to 2020 are in the order of 10 4 ~10 8 Bq / a. Based on this data, the screening of key parameters and sensitivity analysis of dose assessment are carried out.

[0068] Taking 2016 as an example, 3 H, 85 Kr has the largest emission, in the order of 10 8 Bq / a; followed by 234 U, 239 Pu, in the order of 10 7 Bq / a; 241 Pu, 90 Sr, 137 Cs, 241 Am, 238 U, 129 I, 235 U, 60 Co, in the order of 10 6 Bq / a; the rest of the radionuclides are in the order of 10 4 ~10 5 Bq / a. The typical population exposed to the site is divided into four categories: A is the staff of other industrial enterprises around the site; B is the temporary staff in the site; C is the nearest resident group to the site; D is the security personnel in the site.

[0069] (2) Preliminary assessment of the dose of the typical population The inner diameter of the exhaust pipe of the site, the monthly emission data of airborne effluent, and the daily meteorological data were sorted out to form the annual emission amount and emission rate of airborne effluent, and the concentration distribution simulation input data such as the annual average rainfall of different wind directions, the annual average wind speed of different wind directions, and so on. The CFD method was used to carry out the concentration field distribution simulation of the airborne effluent emission. The dose assessment formulas (1)-(13) were used to calculate the exposure dose of four typical groups of people in combination with the main exposure pathways of the typical groups of people.

[0070] The exposure pathways of B and D groups of people are three, including air immersion external exposure, surface deposition external exposure, and inhalation internal exposure, and the dose of food intake internal exposure is 0. The exposure pathways of C group of public members are four, including air immersion external exposure, surface deposition external exposure, inhalation internal exposure, and food intake internal exposure. Taking the A group of people as an example, Table 2 is the preliminary evaluation results of the group dose of the A group of people in 2016.

[0071] Table 2 Preliminary evaluation results of the group dose of the A group of people

[0072] (3) According to the preliminary evaluation results of the dose, the type of the pathway is determined and the nuclides are screened.

[0073] Figure 3 The time sequence variation characteristics of the exposure dose of the typical groups of people obtained by the CFD concentration simulation and the dose assessment of the source items released by the nuclear facility from 2016 to 2020 are shown. In the figure, the green line is the emission amount of all nuclides, the light blue line is the emission amount of Pu nuclides, and the red line is the exposure dose of the A group of people. 239 As shown in the figure, the emission amount of the airborne effluent of the nuclear facility shows a growth trend from 2016 to 2019, and a significant decrease in 2020, which is obviously inconsistent with the time sequence variation characteristics of the exposure dose of the A, B, C, and D typical groups of people. The highest value of the exposure dose of different typical groups of people appears in different years. For example, the highest value of the exposure dose of the A and B representative groups of people appears in 2020, and the highest value of the C and D groups appears in 2018. Among the 15 nuclides released by the target site, the nuclide with the largest contribution to the dose is Pu, which is the key nuclide, and its release amount and concentration in the environment air reach the highest in 2020, followed by 2018, which is relatively consistent with the trend of the exposure dose of the A and B groups of people, but there is a difference in the time point of the highest value of the exposure dose of the C and D groups. This shows that in addition to the key nuclide, attention should also be paid to the influence of other main nuclides on the personal effective dose of the public. 239

[0074] After calculation, for the A group of people, the key pathway is inhalation internal exposure. According to Table 3, the inhalation internal exposure dose contributes more than 99% to the total dose from 2016 to 2020. The nuclide that contributes more than 10% to the inhalation internal exposure pathway is 239Pu, and the dose contribution rate accounts for between 81.14% and 89.84%. In addition to 239 ​In addition to Pu, the nuclides that contribute more than 5% to the total dose are 234 U, 241 Am, 240 Pu, and 3 H. According to the dose proportion of each irradiation pathway, there is no main pathway for the A group of people. Since the dose contribution rates of air immersion external exposure and surface deposition external exposure are less than 1%, the sensitivity analysis of the above two pathways is not performed. The results of the 'pathway-nuclide' analysis of the B and D groups of people are consistent with the conclusion of A, which is not described here.

[0075] Table 3 Main parameters for dose evaluation of each irradiation pathway for the A group of people

[0076] Similarly, according to the calculation of the dose and contribution proportion of each irradiation pathway, for the C group of people, the key irradiation pathway is inhalation internal exposure. As shown in Table 6, the dose of inhalation internal exposure contributes more than 98% to the total dose from 2016 to 2020. The nuclides that contribute more than 10% to the inhalation internal exposure pathway are 239 Pu, and the dose contribution rate is between 81.14% and 89.84% from 2016 to 2020. In addition to 239 Pu, the nuclides that contribute more than 5% to the total dose of the adult group are 234 U, 241 Am, 240 Pu, and 3 H. There is no main irradiation pathway for the C group of people. Among the secondary irradiation pathways, the dose proportion of ingestion internal exposure is 0.66% to 1.56%, 239 Pu, and 3 H are the main contributing nuclides of this pathway. Since the dose contribution rates of air immersion external exposure and surface deposition external exposure are less than 1%, the sensitivity analysis of the above two pathways is not performed.

[0077] Table 4 Main parameters for dose evaluation of each irradiation pathway for the C group of people

[0078] Combining Tables 1, 3, and 4, a 'irradiation pathway-nuclide-key parameter' matrix is established to screen out the key parameters that need to be analyzed for sensitivity analysis, a total of 5 nuclides and 16 parameters, as shown in Table 5. Inhalation internal exposure is the key irradiation pathway, and the analysis of 239 Pu, 234 U, 241 Am, 240 Pu, and 3The sensitivity of key parameters such as residence factor of H nuclides, personal annual air intake, and inhalation dose conversion factor. The proportion of internal exposure by ingestion in the C group is more than 1%, and as a secondary exposure pathway, the sensitivity of the parameters related to internal exposure by ingestion is analyzed.

[0079] Table 5. Key parameters for dose assessment for sensitivity analysis

[0080] (4) Sensitivity analysis of dose assessment parameters EFAST analysis is implemented using commercial software or python programming. Sensitivity analysis is performed on the 16 parameters of the 5 nuclides obtained in Table 5. Each parameter is sampled 80 times to obtain 1280 parameter combinations, each sample including 16 parameter variables. The sampled parameter combinations are used as input variables, and the dose calculation value is used as the output variable. The first-order sensitivity and global sensitivity coefficients of each parameter are calculated to analyze the influence of each parameter on the output variable. According to the parameter sensitivity classification standard, the 16 parameters are classified according to their sensitivity.

[0081] a. First-order sensitivity index results and analysis The first-order sensitivity index reflects the degree of influence of the independent action of each parameter variable on the change in dose. As shown in Table 5, the independent sensitivity of the 16 parameters is ranked from high to low as Rf, Rv, G3- v , Up, Fp, Tv, . The contribution of other parameters such as Rsf, G3- 239 Pu, G3- 234 U is close to 0. As shown in the table, the sensitivity of the 16 parameters can be divided into two levels. When setting parameters, attention should be paid to 238 Pu and 241 Pu inhalation dose conversion factor. The sensitivity index of other parameters is <0.05, which is a non-sensitive parameter. The analysis results are shown in Table 6.

[0082] Table 6. First-order sensitivity classification of parameter variables

[0083] b. Global sensitivity index results and analysis The global sensitivity index takes into account the influence of the coupling between parameter variables on the change in dose. According to the global sensitivity index analysis results as shown in Table 7. The global sensitivity of the 16 parameters relative to the dose is ranked from high to low as Rf, Rv, G3- 239 Pu, G3- 241 Am, Up, Fp, Tv, Rsf, G3- 234The contribution of U and other parameters is close to 0. Compared with the first-order sensitivity ranking of the parameter variables in Table 5, the high sensitivity parameters are consistent, which are the residence factor Rf and the personal annual air intake Rv, and the interaction between parameters enhances the sensitivity of the two parameters. Due to the interaction between parameters, the partial variable sensitivity ranking based on global sensitivity analysis changes, such as the medium sensitivity parameters 239 Pu inhalation dose conversion factor G3- 239 Pu and 240 Pu inhalation dose conversion factor G3- 240 Pu.

[0084] Table 7 Global sensitivity ranking of parameter variables

[0085] (5) Local correction of sensitive parameters According to the results of key parameter sensitivity analysis, the high sensitivity and medium sensitivity parameters are localized. According to the living habits of four types of typical population and the survey results of respiratory rate, the residence factor and the local value of respiratory rate are shown in Table 8. The local correction value of the sensitivity parameter is used to evaluate the representative population group dose.

[0086] The relative change rate of the dose evaluation results is respectively: A is 0.42; B is 1.06; C is 0.70, and D is 1.25. The population group dose of A and C is reduced, and the population group dose of B and D is increased. This shows that it is necessary to carry out parameter sensitivity and localization research to improve the accuracy of the evaluation results, and to provide data and method support for the optimization of target plant discharge and future development space planning layout.

[0087] Table 8 Sensitivity parameter localization analysis

[0088] According to the parameter values after local correction, recalculate formula (1) to (13) to obtain the final evaluation results.

[0089] Those skilled in the art can understand that the above description is only preferred embodiments of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, and those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for assessing radiation dose in nuclear facilities based on parameter sensitivity analysis optimization, characterized in that, Includes the following steps: The parameters involved in the radiation dose assessment are classified according to the method of acquisition into parameters related to the concentration of pollutant migration and diffusion, deterministic parameters, and variable parameters; the variable parameters are those related to the irradiation route, radionuclides, typical populations, and the characteristics of the area where the target nuclear facility is located. The concentration distribution of airborne effluent from the target nuclear facility was simulated and calculated using the CFD method to obtain the values ​​of the parameters related to the concentration of pollutant migration and diffusion. Based on the values ​​of the parameters related to the concentration of pollutant migration and diffusion, the values ​​of the deterministic parameters, and the initial values ​​of the variable parameters, the total radiation dose received by each typical population affected by the target nuclear facility under the corresponding radiation pathway, and the contribution rate of the radiation dose of each radiation pathway to the total radiation dose are calculated. Based on the contribution rate, each of the irradiation pathways is identified as a critical pathway or a non-critical pathway; Screening criteria were set for the identified pathways, and nuclides whose radiation dose contribution rate to the pathway met the screening criteria were selected. The variable parameters associated with the screened nuclides are determined to obtain a matrix of pathways, nuclides, and variable parameters, and all variable parameters in the matrix are used as key parameters. The EFAST algorithm was used to analyze the key parameters to obtain sensitivity parameters for the total radiation dose received by each typical population under the corresponding irradiation pathway, and to distinguish between high-sensitivity parameters and medium-sensitivity parameters. The highly sensitive and moderately sensitive parameters are locally modified, and the initial values ​​are replaced with the locally modified values. Based on the localized correction values, the total radiation dose received by each typical population under the corresponding irradiation pathway was recalculated to obtain the dose assessment results.

2. The evaluation method according to claim 1, characterized in that, The total radiation dose D of each typical population under each radiation pathway is calculated using the following formula:

3. In the formula, i The serial number representing the radionuclide. m The number of radioactive nuclides. D 1i , D 2i , D 3i , D 4i The first i The radiation dose of a radionuclide through four irradiation pathways: external irradiation by air immersion, external irradiation by surface deposition, internal irradiation by inhalation, and internal irradiation by ingestion. R f For residency factors; The radiation dose for each irradiation pathway is the sum of the radiation doses of all radionuclides under that irradiation pathway.

4. The evaluation method according to claim 2, characterized in that, Under the air immersion external irradiation, the variable parameters include the residence factor, the dose reduction factor caused by building shielding, and the smoke cloud immersion irradiation dose factor; Under external irradiation of the surface deposits, the variable parameters include the residence factor, resuspension factor, external irradiation dose conversion factor of the surface deposits, and the deposition time of the nuclide on the ground. Under the inhaled internal irradiation, the variable parameters include the residence factor, respiratory rate, resuspension factor, and inhaled internal irradiation dose conversion factor. Under the ingested internal irradiation, the variable parameters are annual intake, concentration factor, retention share, translocation factor, share of ingested agricultural products from relevant regions, and ingested internal irradiation dose conversion factor.

5. The evaluation method according to claim 1, characterized in that, Screening criteria were set for the identified pathways, and nuclides whose radiation dose contribution rate to the pathway met the screening criteria were selected, including: For the key pathway, the nuclide that contributes the most to the irradiation dose of the pathway is selected as the key nuclide, and the nuclide whose contribution to the irradiation dose exceeds the first set value or whose contribution to the total irradiation dose of all irradiation pathways exceeds the second set value is selected as the main nuclide. Based on the contribution rate of the non-critical pathways, they are further divided into primary pathways with larger contribution rates and secondary pathways with smaller contribution rates. For the main pathway, nuclides that contribute more than a third set value to the irradiation dose of the pathway or contribute more than a fourth set value to the total irradiation dose of all irradiation pathways are selected as the main nuclides. For the secondary pathways, the decision on whether to perform primary nuclide screening is based on the specific value of their contribution rate.

6. The evaluation method according to claim 1, characterized in that, Localized corrections are made to the highly sensitive and moderately sensitive parameters, including: Conduct on-site investigations or experiments in the area where the target nuclear facility is located to obtain values ​​that directly reflect the actual environmental characteristics; Alternatively, select an empirically recommended value for a region with similar environmental characteristics to the area where the target nuclear facility is located.

7. The evaluation method according to claim 1, characterized in that, The parameters related to pollutant migration and diffusion concentration include long-term diffusion factor, ground deposition concentration, and ground air concentration value.

8. The evaluation method according to claim 1, characterized in that, The CFD method is used to simulate and calculate the concentration distribution of airborne effluents from the target nuclear facility, including: Obtain meteorological data for the area where the target nuclear facility is located, including the combined frequency of different wind directions, wind speeds, and stability combinations, annual average rainfall for different wind directions, and annual average wind speed data for different wind directions. Acquire source data, including annual emissions and emission rates of airborne effluents; Centered on the location of the main exhaust stack of the target nuclear facility, a simulation area is set. Using the meteorological data input and source term data as input, a concentration field distribution simulation is performed to obtain the values ​​of parameters related to the concentration of pollutant migration and diffusion at different downwind distances.

9. The evaluation method according to claim 1, characterized in that, The EFAST algorithm was used to analyze the key parameters, including: For each key parameter, a value range is determined. Within the value range, all key parameters are sampled n times to obtain parameter samples An, where A is the total number of key parameters, which is the number of parameter samples in each group. The parameter samples are used as input variables and input into the EFAST algorithm model to obtain the total radiation dose of each typical population under the corresponding irradiation pathway as the output variable. Calculate the contribution rate of each key parameter sample to the variance of the output variable, thereby characterizing the parameter sensitivity; Considering the coupling effect between key parameters, a sensitivity analysis of the interaction between key parameters is conducted, and a global sensitivity index is used to characterize and obtain the sensitivity index value of each key parameter. Based on the sensitivity index values, key parameters are divided into high-sensitivity parameters, medium-sensitivity parameters, and low-sensitivity parameters.

10. The evaluation method according to claim 1, characterized in that, The typical population includes employees of other industrial enterprises around the target nuclear facility, temporary workers at the target nuclear facility site, residents closest to the target nuclear facility, and security personnel at the target nuclear facility site.

11. The evaluation method according to claim 1, characterized in that, The deterministic parameters include the decay constant of the γ nuclide.

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