A method and system for determining shutdown dose rate of a nuclear facility

Abstract

The present application relates to the technical field of Monte Carlo particle transport calculation and radiation safety analysis in nuclear science, and particularly relates to a method and system for determining shutdown dose rate of nuclear facilities, the method comprising: S1, calculating the generation rate of each photon generated by the decay of each secondary radionuclide and summing up to obtain the total generation rate of all photons corresponding to each collision when each collision occurs; according to the ratio between the generation rate of each photon at each collision and the total generation rate at the collision, sampling photons from all the photons generated at each collision, taking the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision, and performing photon transport calculation to count the photons in the target region, and combining the photon flux-dose conversion factor to obtain the shutdown dose rate distribution of the photons in the target region. The shutdown dose rate can be quickly and accurately calculated to provide accurate data support for subsequent processing of nuclear facilities.

Description

Technical Field

[0001] This invention relates to the field of Monte Carlo particle transport calculation and radiation safety analysis technology in nuclear science, and particularly to a method and system for determining the shutdown dose rate of a nuclear facility. Background Technology

[0002] During the operation of nuclear facilities, components and materials are easily activated by radiation to produce radioactive nuclides. These radioactive nuclides may decay and emit photons. These photons penetrate the components and form a photon radiation field around the nuclear facility, posing a potential radioactive hazard to the environment and personnel. Radiation safety analysis needs to study and analyze the dose rate distribution of these photons on the surrounding environment during the operation of the nuclear facility and after the facility is suspended or shut down.

[0003] There are two main methods for calculating the shutdown dose rate: the rigorous two-step method and the direct one-step method. The drawback of the rigorous two-step method is that obtaining an accurate shutdown dose rate distribution requires a fine mesh generation, but processing a large number of meshes inevitably consumes a significant amount of time, reducing computational efficiency. The direct one-step method for calculating the decay photon dose rate after neutron irradiation can only handle the one-step decay process of some nuclides and cannot handle multi-step reactions and cascade decays. The incomplete consideration of the activation process leads to inaccurate calculation results, affecting subsequent processing. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method and system for determining the shutdown dose rate of a nuclear facility.

[0005] The technical solution of the method for determining the shutdown dose rate of a nuclear facility according to the present invention is as follows:

[0006] S1. Construct a neutron transport model for a nuclear facility. In the neutron transport model, when a neutron collides with any preset nuclide, the generation rate of each photon produced by the decay of each secondary radioactive nuclide corresponding to the preset nuclide that collides is calculated based on the target irradiation duration. In this model, multiple preset nuclides are determined according to the material of the nuclear facility, and the operating time of the nuclear facility is determined as the target irradiation duration.

[0007] S2. In the neutron transport model, S1 is executed once each time a collision occurs, and the generation rate of each photon for each secondary radionuclide is summed to obtain the total generation rate of all photons corresponding to each collision.

[0008] S3. Based on the ratio between the generation rate of each photon at each collision and the total generation rate at that collision, sample photons from all photons produced at each collision, use the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision, and perform photon transport calculation to group and count photons in the target area, and combine the photon flux-dose conversion factor to obtain the photon shutdown dose rate distribution in the target area.

[0009] The beneficial effects of the method for determining the shutdown dose rate of a nuclear facility according to the present invention are as follows:

[0010] It solves the problem that traditional one-step shutdown dose rate calculation cannot handle multi-step reactions and cascade decays, and can quickly and accurately calculate the shutdown dose rate, providing accurate data support for subsequent nuclear facility processing.

[0011] The technical solution of the shutdown dose rate determination system for nuclear facilities according to the present invention is as follows:

[0012] This includes a calculation module, a repeated call to the summation module, and a determination module;

[0013] The construction calculation module is used to: construct a neutron transport model of a nuclear facility. In the neutron transport model, when a neutron collides with any preset nuclide, based on the target irradiation duration, calculate the generation rate of each photon produced by the decay of each secondary radioactive nuclide corresponding to the preset nuclide that collides. In this model, multiple preset nuclides are determined according to the materials of the nuclear facility, and the operating time of the nuclear facility is determined as the target irradiation duration.

[0014] The repeated call to the summation module is used to: in the neutron transport model, call the construction calculation module once each time a collision occurs to sum the generation rate of each photon for each secondary radionuclide, and obtain the total generation rate of all photons corresponding to each collision;

[0015] The determining module is used to: sample photons from all photons produced in each collision based on the ratio between the generation rate of each photon in each collision and the total generation rate in that collision; use the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision; perform photon transport calculations to group and count photons in the target region; and combine the photon flux-dose conversion factor to obtain the photon shutdown dose rate distribution in the target region.

[0016] The beneficial effects of the nuclear facility shutdown dose rate determination system of the present invention are as follows:

[0017] It solves the problem that traditional one-step shutdown dose rate calculation cannot handle multi-step reactions and cascade decays, and can quickly and accurately calculate the shutdown dose rate, providing accurate data support for subsequent nuclear facility processing.

[0018] The present invention provides a storage medium storing instructions that, when read by a computer, cause the computer to execute a method for determining the shutdown dose rate of a nuclear facility as described in any of the preceding claims.

[0019] An electronic device according to the present invention includes a processor and the above-described storage medium, wherein the processor executes instructions in the storage medium. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a method for determining the shutdown dose rate of a nuclear facility according to an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of a shutdown dose rate determination system for a nuclear facility according to an embodiment of the present invention. Detailed Implementation

[0022] like Figure 1 As shown, an embodiment of the present invention provides a method for determining the shutdown dose rate of a nuclear facility, comprising the following steps:

[0023] S1. Construct a neutron transport model for a nuclear facility. In the neutron transport model, when a neutron collides with any preset nuclide, calculate the generation rate of each photon produced by the decay of each secondary radioactive nuclide corresponding to the preset nuclide that collides, based on the target irradiation duration. Among them, multiple preset nuclides are determined according to the materials of the nuclear facility, and the operating time of the nuclear facility is determined as the target irradiation duration.

[0024] Among them, several pre-defined nuclides include: Fe-56, Ni-58, Mn-55, Cr-24, Mo-98, V-51, etc.

[0025] S2. In the neutron transport model, S1 is executed once for each collision to sum the generation rate of each photon for each secondary radionuclide and obtain the total generation rate of all photons for each collision.

[0026] S3. Based on the ratio between the generation rate of each photon at each collision and the total generation rate at that collision, sample photons from all photons produced at each collision, use the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision, and perform photon transport calculation to group and count photons in the target area, and combine the photon flux-dose conversion factor to obtain the shutdown dose rate distribution of photons in the target area.

[0027] The target area can be set according to the actual situation, such as on the nuclear facility or in the area surrounding the nuclear facility.

[0028] Optionally, in the above technical solution, in S1, calculating the generation rate of each photon for each secondary radionuclide corresponding to the preset nuclide that collides includes:

[0029] S10. When a neutron collides with any preset nuclide, the neutron flux density at the collision point is obtained using a collision estimation method. Based on the target irradiation duration and the functional relationship between the irradiation duration, energy group, and production coefficient of each secondary radionuclide corresponding to the preset nuclide that collides, the production coefficient of each secondary radionuclide corresponding to the preset nuclide that collides is calculated. Combined with the neutron flux density at the collision point and the relevant decay data of each secondary radionuclide corresponding to the preset nuclide that collides, the production rate of each photon of each secondary radionuclide corresponding to the preset nuclide that collides is calculated. The decay data refers to the branching ratio, energy, half-life, and other data of nuclide decay, which can be directly obtained from the evaluation library.

[0030] Optionally, in the above technical solution, the process of obtaining the functional relationship between the irradiation duration, energy group, and production coefficient for each secondary radionuclide includes:

[0031] S01. Obtain the nucleon density of each secondary radionuclide produced by each preset nuclide under different preset irradiation durations and different preset energy groups, specifically:

[0032] Neutron activation calculations were performed on each preset nuclide to obtain the nucleon density of each secondary radionuclide produced by each preset nuclide under different preset irradiation durations and different preset energy groups.

[0033] S02. Based on the nucleon density of any secondary radionuclide produced under different preset irradiation durations and different preset energy groups, calculate the production coefficient of the secondary radionuclide under different irradiation durations and different energy groups. Based on the production coefficient of the secondary radionuclide under different irradiation durations and different energy groups, fit the functional relationship between the irradiation duration, energy group and production coefficient of the secondary radionuclide, until the functional relationship between the irradiation duration, energy group and production coefficient of each secondary radionuclide is obtained.

[0034] Specifically, this is achieved through S001 to S003:

[0035] S001. Before calculating neutron transport, the neutron energy is divided into N neutron energy groups according to the problem type.

[0036] S002. For all common nuclides, use the neutron energy groups divided in step S001 according to N different irradiation times t. nBy performing neutron activation calculations for each energy group, the density of secondary radioactive nuclide j produced by different nuclides i under neutron irradiation in different energy groups was obtained. Further calculations yielded the values ​​of different nuclides i under N different irradiation durations in the neutron energy group g. n The corresponding neutron flux density φ gn,0 The production coefficient C of radionuclide j produced under incident neutron irradiation j,i,gn (t n ):

[0037]

[0038] S003. Based on the production coefficients of radionuclide j under N different irradiation durations calculated in S002, fit the irradiation duration t of different nuclides i under arbitrary irradiation of incident neutrons in energy group gn. i The production coefficient of radionuclide j produced by irradiation is established, and the functional relationship is as follows:

[0039] C j,i,gn (t i ) = fit(C j,i,gn (t n ))

[0040] Specifically, this is achieved through S100 to S102:

[0041] S100. Sampling and generating all secondary radionuclides produced in each collision: At each collision, first sample the i-th pre-defined nuclide that occurred during the collision, and then use the functional relationship C... j,i,gn (t i ) = fit(C j,i,gn (t n The target irradiation duration t of the preset nuclide i is obtained. r The production coefficient C of the j-th secondary radionuclide j j,i,gn (t r The neutron flux density φ at the collision point is obtained using the collision estimation method. gn Then, after the target irradiation time t r Then, cool for a preset time t. c The nucleon density of the j-th secondary radionuclide j produced is ρ i,j,gn The following relationship exists:

[0042]

[0043] Where, λ j Let be the decay constant of radionuclide j;

[0044] S101. Calculate the generation rate of each photon for each secondary radionuclide corresponding to the preset nuclide in each collision:

[0045] For the j-th secondary radionuclide, it may emit photons of various energies, among which E k Let λ represent the energy of the k-th photon, where k is a positive integer, and let λ represent the decay constant of the j-th secondary radionuclide. j The branch ratio b to the energy of the emitted k-th photon k The nucleon density can be obtained by querying the relevant decay database of the j-th secondary radionuclide, and then ρ is given. i,j,gn The production rate I of the k-th photon emitted by the j-th secondary radionuclide j,k for:

[0046]

[0047] Where N0 is Avogadro's constant and M is the atomic weight of the nuclide.

[0048] S102. Calculate the total generation rate of all photons corresponding to each collision: Considering that a preset nuclide may produce multiple secondary radioactive nuclides under neutron irradiation, and each secondary radioactive nuclide may emit photons of multiple energies, the total generation rate I of the photons produced by the i-th preset nuclide at the collision point under the target irradiation duration is... i for:

[0049]

[0050] S103. Based on the ratio between the generation rate of each photon at each collision and the total generation rate at that collision, sample photons from all photons produced at each collision, use the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision, and perform photon transport calculation to group and count photons in the target area, and combine the photon flux-dose conversion factor to obtain the shutdown dose rate distribution of photons in the target area.

[0051] Optionally, the above technical solution also includes:

[0052] S4. Assess the photon shutdown dose rate distribution in the target area to determine whether a protective alert should be issued. Specifically:

[0053] 1) Based on the calculated shutdown dose rate, assess whether maintenance personnel can immediately enter for maintenance, and the duration of their stay;

[0054] 2) Based on the calculated shutdown dose rate, assess whether the surrounding environment meets the radiation protection requirements. If it does not meet the radiation protection requirements, determine what radiation protection measures need to be adopted.

[0055] 2) Based on the calculated shutdown dose rate, set the cooling time of the nuclear facility appropriately.

[0056] The present invention will now be described through another embodiment, which specifically includes:

[0057] S1000. Before the neutron transport calculation, the neutron energy from 0 to 20 MeV is divided into 172 neutron energy groups according to the problem type. Neutron activation calculations are then performed for each of the 172 neutron energy groups for all common nuclides under different irradiation times (10 s, 100 s, 1000 s, 104 s, 105 s, 106 s, 107 s, 108 s, 109 s, 1010 s) to obtain the production coefficients of secondary radionuclides for different nuclides under neutron irradiation in different energy groups.

[0058]

[0059] in, The density of secondary radioactive nuclide j produced by different nuclides i under neutron irradiation in different energy groups. ρ i,0 Density of nuclide i; φ gn,0 Let be the neutron flux density of the gn-th group.

[0060] S1001. Based on the above calculation results, the arbitrary irradiation time t of different nuclides i under incident neutrons in energy group gn is fitted. i The production coefficient of radionuclide j produced by irradiation was determined, and a database was established.

[0061] C j,i,gn (t i ) = fit(C j,i,gn (t n ))

[0062] During neutron transport, at each collision, the initial nuclide i is sampled, and the irradiation duration t of nuclide i is obtained by interpolation from a database. r The production coefficient C of radionuclide j j,i,gn (t r The neutron flux density φ at the collision point is estimated from the collision data. gn Then after irradiation time t r Recooling time t c The nucleon density of the secondary radionuclide j produced is ρ i,j,gn The following relationship exists:

[0063]

[0064] Where, λ j Let be the decay constant of radionuclide j.

[0065] S1002. For a radioactive nuclide j, it may emit photons of various energies. Its decay constant λj and the branching ratio bk of the emitted photon with energy Ek can be obtained by querying relevant decay databases. Then the nuclide density is ρ. i,j,g The production rate of decay photons with energy Ek emitted by radioactive nuclide j is:

[0066]

[0067] Where N0 is Avogadro's constant and M is the atomic weight of the nuclide.

[0068] S1003. Considering that an initial nuclide may produce multiple radioactive nuclides under neutron irradiation, and each radioactive nuclide may emit photons of multiple energies, the total probability that nuclide i at the collision point will produce photons under a given irradiation scheme is:

[0069]

[0070] Based on the total probability of photons being generated in each collision, photons are generated by sampling using the source sampling method: first, the energy of the generated photons is sampled according to the generation probability of each type of photon, and then the total probability of photons being generated in each collision is assigned to the weight of the sampled photons.

[0071] After obtaining the decay photon source through each collision sampling, photon transport calculations are performed directly. Photons are grouped and counted in the target region, and the photon dose rate distribution in the target region is obtained by combining the corresponding photon flux-dose conversion factor.

[0072] In the above embodiments, although the steps are numbered S1, S2, etc., they are only specific embodiments given in this application. Those skilled in the art can adjust the execution order of S1, S2, etc. according to the actual situation, which is also within the protection scope of this invention. It can be understood that in some embodiments, some or all of the above embodiments may be included.

[0073] like Figure 2 As shown, a shutdown dose rate determination system 200 for a nuclear facility according to an embodiment of the present invention includes a construction calculation module 210, a repeated call summation module 220, and a determination module 230.

[0074] The calculation module 210 is used to: construct a neutron transport model for a nuclear facility. In the neutron transport model, when a neutron collides with any preset nuclide, the generation rate of each photon produced by the decay of each secondary radioactive nuclide corresponding to the preset nuclide that collides is calculated based on the target irradiation duration. Among them, multiple preset nuclides are determined according to the materials of the nuclear facility, and the operating time of the nuclear facility is determined as the target irradiation duration.

[0075] The repeated invocation of the summation module 220 is used to: in the neutron transport model, call the construction calculation module 210 once each time a collision occurs to sum the generation rate of each photon for each secondary radionuclide, and obtain the total generation rate of all photons corresponding to each collision;

[0076] The determination module 230 is used to: sample photons from all photons produced in each collision based on the ratio between the generation rate of each photon in each collision and the total generation rate in that collision, and perform photon transport calculations to group and count photons in the target area, use the total generation rate corresponding to each collision as the weight of the sampled photons corresponding to each collision, and combine the photon flux-dose conversion factor to obtain the shutdown dose rate distribution of photons in the target area.

[0077] Optionally, in the above technical solution, the computing module 210 is further specifically used for:

[0078] When a neutron collides with any preset nuclide, the neutron flux density at the collision point is obtained using a collision estimation method. Based on the target irradiation duration and the functional relationship between the irradiation duration, energy group, and production coefficient of each secondary radionuclide corresponding to the preset nuclide that collided, the production coefficient of each secondary radionuclide corresponding to the preset nuclide that collided is calculated. Combined with the neutron flux density at the collision point and the relevant decay data of each secondary radionuclide corresponding to the preset nuclide that collided, the production rate of each photon of each secondary radionuclide corresponding to the preset nuclide that collided is calculated.

[0079] Optionally, the above technical solution also includes a function relationship calculation module, which is used for:

[0080] Obtain the nucleon density of each secondary radionuclide produced by each preset nuclide under different preset irradiation durations and different preset energy groups;

[0081] Based on the nucleon density of any secondary radionuclide produced under different preset irradiation durations and different preset energy groups, the production coefficient of the secondary radionuclide under different irradiation durations and different energy groups is calculated. Based on the production coefficient of the secondary radionuclide under different irradiation durations and different energy groups, the functional relationship between the irradiation duration, energy group and production coefficient corresponding to the secondary radionuclide is fitted, until the functional relationship between the irradiation duration, energy group and production coefficient corresponding to each secondary radionuclide is obtained.

[0082] Optionally, in the above technical solution, the function relationship calculation module is also specifically used for:

[0083] Neutron activation calculations were performed on each preset nuclide to obtain the nucleon density of each secondary radionuclide produced by each preset nuclide under different preset irradiation durations and different preset energy groups.

[0084] Optionally, the above technical solution also includes an evaluation module, which is used for:

[0085] Assess the photon shutdown dose rate distribution in the target area to determine whether to issue a protective alert.

[0086] The parameters and steps of each unit module in the nuclear facility shutdown dose rate determination system 200 of the present invention described above for implementing their respective functions can be referred to the parameters and steps in the embodiments of the nuclear facility shutdown dose rate determination method described above, and will not be repeated here.

[0087] An embodiment of the present invention provides a storage medium storing instructions, which, when read by a computer, cause the computer to execute any of the above-mentioned methods for determining the shutdown dose rate of a nuclear facility.

[0088] An electronic device according to an embodiment of the present invention includes a processor and the aforementioned storage medium, wherein the processor executes instructions stored in the storage medium. The electronic device may be a computer, mobile phone, or the like.

[0089] Those skilled in the art will know that this invention can be implemented as a system, method, or computer program product.

[0090] Therefore, this disclosure can be implemented in the following forms: it can be entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "system." Furthermore, in some embodiments, the invention can also be implemented as a computer program product in one or more computer-readable media, the computer-readable medium containing computer-readable program code.

[0091] Any combination of one or more computer-readable media may be used. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in connection with an instruction execution system, apparatus, or device.

[0092] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of determining a shutdown dose rate of a nuclear facility, characterized by, The method comprises the steps of: S1, constructing a neutron transport model of a nuclear facility, wherein, when a neutron collides with any preset nuclide, the production rate of each photon generated by the decay of each secondary radioactive nuclide corresponding to the preset nuclide is calculated based on a target irradiation time, wherein, according to the materials of the nuclear facility, a plurality of preset nuclides are determined, and the operation time of the nuclear facility is determined as the target irradiation time; S2, in the neutron transport model, S1 is executed once each time a collision occurs, and the production rate of each photon of each secondary radioactive nuclide is summed to obtain the total production rate of all photons corresponding to each collision; S3, according to the ratio between the production rate of each photon at each collision and the total production rate at the collision, photons are sampled from all the photons produced at each collision, the total production rate corresponding to each collision is taken as the weight of the sampled photons corresponding to each collision, and photon transport calculation is performed to count the photons in the target region, and the photon fluence-dose conversion factor is combined to obtain the shutdown dose rate distribution of the photons in the target region.

2. A method of determining a shutdown dose rate of a nuclear facility according to claim 1, characterized in that, The production rate of each photon of each secondary radioactive nuclide corresponding to the preset nuclide that collides is calculated, comprising: When a neutron collides with any preset nuclide, the neutron flux density at the collision point is obtained by using a collision estimation method, and the production coefficient of each secondary radioactive nuclide corresponding to the preset nuclide that collides is calculated according to the function relationship between the target irradiation time, the irradiation time of each secondary radioactive nuclide corresponding to the preset nuclide that collides, the energy group and the production coefficient, and the neutron flux density at the collision point and the related decay data of each secondary radioactive nuclide corresponding to the preset nuclide that collides are combined to calculate the production rate of each photon of each secondary radioactive nuclide corresponding to the preset nuclide that collides.

3. A method of determining a shutdown dose rate of a nuclear facility according to claim 2, characterized in that, The process of obtaining the function relationship between the irradiation time, the energy group and the production coefficient of each secondary radioactive nuclide comprises: Obtaining the nuclide density of each secondary radioactive nuclide generated by each preset nuclide under different preset irradiation times and different preset energy groups; According to the nuclide density of any secondary radioactive nuclide generated under different preset irradiation times and different preset energy groups, the production coefficient of the secondary radioactive nuclide under different irradiation times and different energy groups is calculated, and the function relationship between the irradiation time, the energy group and the production coefficient of the secondary radioactive nuclide is fitted according to the production coefficient of the secondary radioactive nuclide under different irradiation times and different energy groups, until the function relationship between the irradiation time, the energy group and the production coefficient of each secondary radioactive nuclide is obtained.

4. A method of determining a shutdown dose rate of a nuclear facility according to claim 3, characterized in that, Obtaining the nuclide density of each secondary radioactive nuclide generated by each preset nuclide under different preset irradiation times and different preset energy groups comprises: Performing neutron activation calculation on each preset nuclide to obtain the nuclide density of each secondary radioactive nuclide generated by each preset nuclide under different preset irradiation times and different preset energy groups.

5. A method of determining the shutdown dose rate of a nuclear installation according to any one of claims 1 to 4, characterized in that, Further comprising: The photon shutdown dose rate distribution of the target region is evaluated to determine whether to issue a protection reminder.

6. A shutdown dose rate determination system for a nuclear facility, characterized by, The method comprises a calculation module, a repeated summation module and a determination module; The calculation module is configured to construct a neutron transport model of the nuclear facility, and calculate, in the neutron transport model, a generation rate of each photon generated by decay of each secondary radionuclide corresponding to a preset nuclide colliding with a neutron, based on a target irradiation time, wherein a plurality of preset nuclides are determined according to materials of the nuclear facility, and the operation time of the nuclear facility is determined as the target irradiation time. The repeated summation module is configured to call the calculation module once each time a collision occurs in the neutron transport model, sum the generation rate of each photon of each secondary radionuclide, and obtain a total generation rate of all photons corresponding to each collision. The determination module is configured to sample photons from all photons generated at each collision according to a ratio between the generation rate of each photon at each collision and the total generation rate at the collision, take the total generation rate corresponding to each collision as a weight of the sampled photons corresponding to each collision, and perform photon transport calculation to count photons in groups in a target region and obtain a photon shutdown dose rate distribution of the target region in combination with a photon flux-dose conversion factor.

7. A nuclear facility shutdown dose rate determination system according to claim 6, wherein, The calculation module is further configured to: When a collision occurs between a neutron and any preset nuclide, a collision estimation method is used to obtain a neutron flux density at a collision point, and a generation coefficient of each secondary radionuclide corresponding to the preset nuclide colliding with the neutron is calculated according to a function relationship between the target irradiation time, the irradiation time of each secondary radionuclide corresponding to the preset nuclide colliding with the neutron, the energy group and the generation coefficient, and the generation rate of each photon of each secondary radionuclide corresponding to the preset nuclide colliding with the neutron is obtained in combination with the neutron flux density at the collision point, and the related decay data of each secondary radionuclide corresponding to the preset nuclide colliding with the neutron.

8. A nuclear facility shutdown dose rate determination system according to claim 7, wherein, The function relationship calculation module is further configured to: Obtain the nuclide density of each secondary radionuclide generated by each preset nuclide under different preset irradiation times and different preset energy groups. Calculate the generation coefficient of the secondary radionuclide under different irradiation times and different energy groups according to the nuclide density of any secondary radionuclide generated under different preset irradiation times and different preset energy groups, and fit the function relationship between the irradiation time, the energy group and the generation coefficient corresponding to the secondary radionuclide until the function relationship between the irradiation time, the energy group and the generation coefficient corresponding to each secondary radionuclide is obtained.

9. A nuclear facility shutdown dose rate determination system according to claim 8, wherein, The function relationship calculation module is further configured to: Perform neutron activation calculation on each preset nuclide to obtain the nuclide density of each secondary radionuclide generated by each preset nuclide under different preset irradiation times and different preset energy groups.

10. A system for determining the dose rate of a burnback agent based on nuclide activation according to any one of claims 6 to 9, characterized in that The evaluation module is configured to: The photon build-up dose rate distribution of the target region is evaluated to determine whether to issue a protection alert.

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