Large-scale three-dimensional radiation dose field distribution simulation method based on the pointed Monte Carlo method

Abstract

A large-scale three-dimensional radiation dose field distribution simulation method based on the pointed Monte Carlo method uses constructive solid geometry to perform geometric modeling and material modeling on the nuclear facility to be simulated, sets the distribution of radioactive sources in the nuclear facility and performs fixed source calculation to solve the neutron / photon transport equation; the global response of all pseudo-particle tracks corresponding to all particle states is counted to obtain the relative distribution of the three-dimensional radiation dose field, thereby calculating the importance parameters to guide the particle transport process of the Monte Carlo fixed source calculation; finally, the real three-dimensional radiation dose field distribution is obtained through Monte Carlo simulation, which is used for the rapid evaluation of the cumulative dose rate of relevant practitioners in large nuclear facilities or the rapid screening of shielding schemes for large nuclear facilities. The present invention can realize the rapid modeling and analysis of the three-dimensional radiation dose field of large nuclear facilities, and provide technical support for the radiation protection and shielding design of large nuclear facilities.

Description

Technical Field

[0001] The present invention relates to a technology in the field of radiation protection of large nuclear facilities, specifically a large three-dimensional radiation dose field distribution simulation method based on a pointed Monte Carlo method. Background Art

[0002] When using the Monte Carlo method to calculate the shielding of large nuclear facilities, we face the "low probability-deep penetration" problem, which makes it difficult (or even impossible) to model the radiation dose field of large nuclear facilities. In order to effectively support the radiation protection of large nuclear facilities in my country and effectively solve the "low probability-deep penetration problem", a universal and efficient radiation dose field modeling technology is urgently needed at this stage. Summary of the invention

[0003] The present invention aims at the "small probability-deep penetration" problem faced when using the Monte Carlo method to calculate the radiation dose field of a large nuclear facility, and proposes a large-scale three-dimensional radiation dose field distribution simulation method based on the pointing Monte Carlo method, which can quickly obtain the three-dimensional radiation dose field distribution of large nuclear facilities and their surroundings, and realize the rapid evaluation of the cumulative dose rate of employees in large nuclear facilities and the rapid screening of shielding schemes, thereby effectively promoting the application of the Monte Carlo method in the field of radiation protection of large nuclear facilities. In the real transport process of particles, this method calculates the global response of each particle state through pointing probability, so as to quickly obtain global information. Based on this method, the rapid modeling and analysis of the three-dimensional radiation dose field of large nuclear facilities can be realized, providing technical support for the radiation protection and shielding design of large nuclear facilities.

[0004] The present invention is achieved through the following technical solutions:

[0005] The invention relates to a large-scale three-dimensional radiation dose field distribution simulation method based on a pointed Monte Carlo method. Constructive solid geometry is used to perform geometric modeling and material modeling on a nuclear facility to be simulated, the distribution of radioactive sources in the nuclear facility is set, and fixed source calculation is performed to solve the neutron / photon transport equation; the global response of all pseudo-particle tracks corresponding to all particle states is counted to obtain the relative distribution of the three-dimensional radiation dose field, thereby calculating the importance parameter for guiding the particle transport process of the Monte Carlo fixed source calculation; finally, the real three-dimensional radiation dose field distribution is obtained through Monte Carlo simulation, and the three-dimensional radiation dose field distribution can be used for the rapid evaluation of the cumulative dose rate of relevant practitioners in large-scale nuclear facilities or the rapid screening of shielding schemes for large-scale nuclear facilities.

[0006] The neutron / photon transport equation is: (L+C)·φ=(S+F)·φ+Q s , where L, C, S and F are leakage term, collision term, scattering term and fission term respectively; Q s is the exogenous term; φ is the neutron flux distribution.

[0007] In the fixed source calculation, the transport process of each particle is tracked during the process. When the particle undergoes a nuclear reaction, the global response of the pseudo-particle track corresponding to each particle state is calculated according to the change of the particle's energy E, direction Ω, position P, and weight W. Specifically, the particle's motion track is extended along the particle's motion direction Ω until the boundary of the calculation area, that is, the pseudo-particle track is obtained; the pseudo-particle track describes the one-dimensional radiation dose distribution from the particle position P to the system boundary, specifically: Where: W 0 is the particle weight at the beginning of the pseudo-particle track, ν∑ f is the fission production cross section of the material region through which the pseudoparticle track passes, ∑ t is the total cross-section of a material region that the pseudo-particle track passes through.

[0008] For a large nuclear facility, the material medium is continuously changing, so the fission cross section ν∑ f and total cross section ∑ t It also changes with the material, so in a certain length of l n -l n-1 In the particle track of , the contribution of this particle track to the three-dimensional radiation dose field is obtained by integration, which is: Among them: n-1 is the starting point of the pseudoparticle track, l n is the end point of the pseudoparticle track, R n is the pseudo-particle track at l n -l n-1 The contribution of the particle track to the three-dimensional radiation dose field, W(x) is the radiation dose rate distribution along the pseudo particle track direction, W n-1 It is the value of the radiation dose rate at the starting point of the pseudo-particle track; according to the contribution of the particle track to the three-dimensional radiation dose field, the global response of the pseudo-particle track corresponding to a certain particle state to the radiation dose field is calculated.

[0009] The relative distribution of the three-dimensional radiation dose field is obtained by the following statistical method: Assuming that N particles are simulated in the Monte Carlo fixed source calculation process, each particle will produce M particle states, and a total of N×M particle states will be generated. The radiation dose field distribution of the kth region is specifically: Where: f k is the radiation dose rate in the kth region, is the global response of the jth particle state of the ith particle in the kth region; the superscript “k” represents different spatial regions; the subscript “i” represents different numbers of particles; and the subscript “j” represents different particle states; Represents the global response of the jth particle state corresponding to the ith particle.

[0010] The importance parameter is obtained by normalizing the relative distribution of the three-dimensional radiation dose field, and then ensuring that the survival weight window of a phase space is equal to the normalized radiation dose rate of the phase space, that is, Where: f k is the radiation dose rate in the kth region, max(f k ) is the global maximum radiation dose rate, is the survival weight window of the kth region. Finally, the lower limit and upper limit of the weight window are calculated according to the survival weight window, where the lower limit of the weight window is one third of the survival weight window, and the upper limit of the weight window is one third of the survival weight window.

[0011] Technical Effects

[0012] The present invention proposes for the first time to quickly obtain the approximate distribution of the three-dimensional radiation dose field by counting the global responses of all pseudo-particle tracks corresponding to all particle states, and specifically solves the "small probability-deep penetration" problem when the existing Monte Carlo method is used for shielding analysis of large nuclear facilities. Compared with the prior art, the present invention can realize the rapid modeling and analysis of the radiation dose field of large nuclear facilities, and use the obtained three-dimensional radiation dose field in the radiation protection of large nuclear facilities. Compared with the hybrid Monte Carlo method based on determinism, this method does not need to rely on deterministic programs, but only needs to use constructive solid geometry modeling, and has good geometric universality. Compared with the Monte Carlo self-coupling method, this method can quickly obtain global information, and more efficient iterative convergence ensures higher computational efficiency. The present invention can effectively promote the application of the Monte Carlo method in the field of radiation protection of large nuclear facilities, and can provide technical support for the radiation protection and shielding design of large nuclear facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of the present invention;

[0014] Figure 2 The schematic diagram of calculating the global response based on the pointing Monte Carlo method;

[0015] Figure 3 It is a statistical diagram of the Monte Carlo method in multi-layer media;

[0016] Figure 4 A schematic diagram of a model of the China Fusion Engineering Test Reactor of an embodiment;

[0017] Figure 5 It is a comparison diagram of the effects of the embodiments. DETAILED DESCRIPTION

[0018] This embodiment Figure 4It is implemented in the Chinese Fusion Engineering Test Reactor shown in the figure. The axial dimension of the Fusion Engineering Test Reactor is 16 (meters) × 68 (meters) = 1088 (square meters), and the radial dimension is one sixteenth of the circumference, that is, an angle of 22.5°, thus forming a three-dimensional radiation dose field of a large nuclear facility.

[0019] like Figure 1 As shown, the implementation method of the large radiation dose field modeling technology based on the pointing Monte Carlo method involved in this embodiment specifically includes:

[0020] Step 1: Conduct geometric modeling, material modeling, and radioactive source modeling for the fusion engineering test reactor to determine the type of simulated particles and the total number of particles, including:

[0021] In this embodiment, the radiation dose field of neutrons is simulated, and N=100,000, that is, a total of 100,000 neutrons are simulated.

[0022] In the geometric modeling of this embodiment, Figure 3 The axial section shown in the figure is meshed, the X-axis direction is divided into 160 equal parts, and the Z-axis direction is divided into 340 equal parts, forming a total of 160×340=54400 grids, each of which has a size of 10cm×10cm. Monte Carlo fixed source calculation is started, and the radiation dose rate of all 54400 grids is counted.

[0023] Step 2: Simulate individual neutrons one by one: When a neutron undergoes a nuclear reaction, the state of the neutron will change, and the radiation dose rate of each neutron state in these 54,400 grids is calculated one by one.

[0024] Step 3: Count all pseudo-neutron tracks corresponding to all neutron states: construct the relative distribution of the three-dimensional radiation dose field of the fusion engineering test reactor with the radiation dose rates of all 54,400 grids, and use the relative distribution of the three-dimensional radiation dose field to calculate the importance parameters.

[0025] Step 4: Use the importance parameters obtained in step 3 to perform Monte Carlo calculations to obtain the true three-dimensional radiation dose field distribution.

[0026] Step 5: Using the real three-dimensional radiation dose field distribution obtained in step 4, calculate the cumulative dose rate of employees in the China Fusion Engineering Test Reactor plant over a certain period of time, such as 46 mSv for one year at 15 meters inside the vacuum chamber, and evaluate the feasibility of the shielding scheme for a key equipment in the plant.

[0027] Step 6: Evaluate the calculation effect of this method: set up a control group, use the traditional simulation method and the automatic generation of importance method (MAGIC) to calculate the fusion engineering test reactor model, and obtain two control groups.

[0028] In this embodiment, by comparing the average quality factor The technical effect of the present invention is quantified by the variance distribution of the radiation dose rate, wherein the comparison of the average quality factor is shown in Table 1, and the variance distribution of the radiation dose rate is shown in Table 2. Figure 5 .

[0029] Table 1. The acceleration effect of this embodiment compared with the traditional simulation method and MAGIC method

[0030]

[0031] As shown in Table 1, the present invention achieves good acceleration effect compared with both the traditional simulation method and the MAGIC method. Compared with the traditional simulation method, the acceleration effect is 11.9 times, and compared with the MAGIC method, the acceleration effect is 1.5 times. Therefore, the present method can more efficiently complete the radiation dose field modeling and analysis of large nuclear facilities.

[0032] like Figure 5 As shown in the figure, this method can realize the modeling of the radiation dose field of the China Fusion Engineering Test Reactor, and it only takes 72 minutes to complete the 1088 (m 2 ) scale range. Based on the radiation dose field distribution, the cumulative dose rate at any location within the plant can be calculated, which can then be used for rapid evaluation of the cumulative dose rate of employees and rapid screening of shielding schemes. Therefore, this method can provide technical support for radiation protection and shielding design of large nuclear facilities.

[0033] Compared with the hybrid Monte Carlo method based on determinism, this method does not need to rely on deterministic programs, but only needs to use constructive solid geometry modeling, and has good geometric universality. Compared with the Monte Carlo self-coupling method, this invention can quickly obtain global information, and more efficient iterative convergence ensures higher efficiency. Therefore, the present invention can effectively promote the application of the Monte Carlo method in the field of radiation protection of large nuclear facilities, and can provide technical support for the radiation protection and shielding design of large nuclear facilities.

[0034] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A large-scale three-dimensional radiation dose field distribution simulation method based on the pointed Monte Carlo method, characterized in that: Use constructive solid geometry to perform geometric modeling and material modeling on the nuclear facility to be simulated, set the distribution of radiation sources in the nuclear facility and perform fixed source calculations to solve the neutron / photon transport equations; count the global responses of all pseudo-particle tracks corresponding to all particle states to obtain the relative distribution of the three-dimensional radiation dose field, and then calculate the importance parameters to guide the particle transport process of Monte Carlo fixed source calculations; finally, obtain the real three-dimensional radiation dose field distribution through Monte Carlo simulation; In the fixed source calculation, the transport process of each particle is tracked during the process. When the particle undergoes a nuclear reaction, the global response of the pseudo-particle track corresponding to each particle state is calculated according to the change of the particle's energy E, direction Ω, position P, and weight W. Specifically, the particle's motion track is extended along the particle's motion direction Ω until the boundary of the calculation area, that is, the pseudo-particle track is obtained; the pseudo-particle track describes the one-dimensional radiation dose distribution from the particle position P to the system boundary, specifically: Where: W0 is the particle weight at the beginning of the pseudo particle track, ν∑ f is the fission production cross section of the material region through which the pseudoparticle track passes, ∑ t is the total cross-section of a material region that the pseudo-particle track passes through; In a certain section of length l n -l n-1 In the particle track of , the contribution of this particle track to the three-dimensional radiation dose field is obtained by integration, which is: Where: l n-1 is the starting point of the pseudoparticle track, l n is the end point of the pseudoparticle track, R n is the pseudo-particle track at l n -l n-1 The contribution of the particle track to the three-dimensional radiation dose field, W(x) is the radiation dose rate distribution along the pseudo particle track direction, W n-1 It is the value of the radiation dose rate at the starting point of the pseudo-particle track; the global response of the pseudo-particle track corresponding to a certain particle state to the radiation dose field is calculated according to the contribution of the particle track to the three-dimensional radiation dose field; The relative distribution of the three-dimensional radiation dose field is obtained by the following statistical method: in the Monte Carlo fixed source calculation process, N particles are simulated, each particle will produce M particle states, and a total of N×M particle states are generated. The radiation dose field distribution of the kth region is specifically: Where: f k is the radiation dose rate in the kth region, is the global response of the jth particle state of the ith particle in the kth region; the superscript k represents different spatial regions; the subscript i represents different numbers of particles; and the subscript j represents different particle states; The importance parameter is obtained by normalizing the relative distribution of the three-dimensional radiation dose field, and then ensuring that the survival weight window of a phase space is equal to the normalized radiation dose rate of the phase space, that is, Where: f k is the radiation dose rate in the kth region, max(f k ) is the global maximum radiation dose rate, is the survival weight window of the kth region. Finally, the lower limit and upper limit of the weight window are calculated according to the survival weight window, where the lower limit of the weight window is one third of the survival weight window, and the upper limit of the weight window is one third fifth of the survival weight window.

2. The large-scale three-dimensional radiation dose field distribution simulation method based on the pointing Monte Carlo method according to claim 1 is characterized in that: The neutron / photon transport equation is: (L+C)·φ=(S+F)·φ+Q s , where L, C, S and F are leakage term, collision term, scattering term and fission term respectively; Q s is the exogenous term; φ is the neutron flux distribution.

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