Activation source three-dimensional radioactive intensity inversion method and system based on gamma detector counting and storage medium
By correcting the self-absorption effect using a high-purity germanium detector and the Monte Carlo method, a three-dimensional spatial response function was constructed, solving the problem of accurately obtaining the three-dimensional activity distribution of the activation source during nuclear reactor decommissioning. This enabled high-precision inversion under complex conditions, ensuring the safety and strategy optimization of the nuclear decommissioning process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-18
- Publication Date
- 2026-03-10
AI Technical Summary
During the decommissioning of nuclear reactors, existing technologies struggle to accurately obtain the three-dimensional activity distribution of radionuclides under complex conditions. In particular, when neutron irradiation history information is lacking, the accuracy of traditional forward calculation methods is insufficient, and existing inverse inversion methods lack stability and accuracy in calculating complex radioactive source terms with high density and non-uniform distribution, failing to meet the high standards required for engineering practice.
The characteristic gamma spectrum of the activated source was measured using a high-purity germanium detector, and the self-absorption effect was corrected by the Monte Carlo method. A three-dimensional spatial response function was constructed by combining Monte Carlo simulation, and a set of response equations between detector count and activated source grid activity was established. The three-dimensional activity distribution of the activated source was inverted by solving the set of equations.
This method enables the accurate acquisition of the three-dimensional activity distribution of the activation source without requiring historical neutron irradiation information, improving the stability and accuracy of the calculation and meeting the safety and optimization strategy requirements in the nuclear decommissioning process.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of radiation field calculation during the decommissioning process of nuclear facilities, and specifically relates to a method, system and storage medium for inverting the three-dimensional radioactivity intensity of activated sources based on gamma detector counting. Background Technology
[0002] During the long-term operation of a nuclear reactor, its internal structural materials (such as pressure vessels and shielding layers) are continuously irradiated by neutrons, resulting in complex nuclear activation reactions that generate various radioactive nuclides. This means that even after the reactor is shut down, its critical components remain highly radioactive, constituting a complex radioactive source term that continuously releases high-intensity gamma rays. In this context, accurately determining the radiation dose field at the decommissioning site is an absolute prerequisite for developing safe, efficient, and economical decommissioning plans (such as remote dismantling, waste sorting, and disposal). The core foundation of all this lies in accurately obtaining the three-dimensional activity distribution information of radioactive nuclides within the decommissioned components.
[0003] Currently, the mainstream method for obtaining activity distribution in the industry is forward computation. This method predicts radioactivity by simulating neutron transport and activation processes. Specifically, its implementation typically relies on the coupling of Monte Carlo procedures and activation calculation procedures, or a combination of deterministic procedures and activation procedures. These methods calculate the neutron flux distribution through numerical simulation, and then obtain the activity distribution based on material composition and operational history. However, forward computation technology has a fundamental application bottleneck: its computational accuracy is heavily dependent on complete and accurate input parameters. These parameters include, but are not limited to: detailed geometric models of the facility, elemental composition of materials, and historical neutron flux data over time throughout the entire operational cycle. For many aging nuclear facility components with missing operational history records, complex structures, or difficult-to-explore components, obtaining this detailed input data is extremely difficult, or even infeasible. Therefore, forward computation methods are often insufficiently applicable in such practical decommissioning scenarios and cannot provide reliable source term assessments.
[0004] To address the aforementioned issues, inverse retrieval techniques for radioactive source activity distribution are considered an effective alternative. This technique does not rely on difficult-to-obtain operational history parameters, but rather retrieves the three-dimensional radioactivity intensity of the radioactive source from data obtained through on-site measurements.
[0005] Despite the promising future of inverse inversion technology, research in this field is still in its early stages, with relatively limited publicly available mature methods. Some algorithms proposed in existing research include:
[0006] The overdetermined equations are solved using the Gauss-Seidel iterative method to invert the source term strengths at different locations in space.
[0007] The Tikhonov regularization method based on nonnegative least squares is used for... 137 Two-dimensional inversion was performed using in-situ Cs gamma spectroscopy measurements.
[0008] These methods can currently achieve inverse inversion of radioactive source activity under relatively simple radiation models and gamma spectra, but they face significant challenges in real nuclear decommissioning scenarios. Nuclear decommissioning sites typically contain complex radioactive source terms with high density and non-uniform distribution, and the radiation field is severely interfered with by factors such as geometric structures and material shielding. Existing inverse methods are significantly insufficient in terms of three-dimensional activity distribution inversion capability, computational stability, and accuracy under such complex conditions, making it difficult to meet the high standards of reliability and accuracy required in engineering practice. Their practical application effectiveness urgently needs further verification and improvement.
[0009] In summary, the development of a three-dimensional radioactivity intensity inversion method for activated sources based on gamma detector counting is of great significance for ensuring operational safety and optimizing decommissioning strategies during nuclear decommissioning. Summary of the Invention
[0010] The purpose of this invention is to...
[0011] The objective of this invention is achieved through the following technical solution:
[0012] A method for inverting the three-dimensional radioactivity intensity of an activated source based on gamma detector counting includes:
[0013] The characteristic gamma spectrum of the activated source is obtained by measuring the initial gamma spectrum through a detector and correcting the self-absorption effect based on Monte Carlo simulation to obtain the corrected characteristic gamma spectrum.
[0014] The geometric model of the activation source is meshed to discretize the three-dimensional activity distribution into a vector form;
[0015] Multiple measuring points are arranged at different locations in space to measure the gamma ray count generated by the activation source and record the spatial coordinates of each measuring point;
[0016] The Monte Carlo method was used to construct response models of the detector to the activation source at different measurement points, and the three-dimensional spatial response function of the detector was calculated.
[0017] Based on the three-dimensional spatial response function, a set of response equations between detector count and activation source grid activity is established, and the set of equations is solved to invert the three-dimensional activity distribution of the activation source.
[0018] Furthermore, the initial gamma spectrum is measured using a high-purity germanium detector; the self-absorption effect correction is achieved by simulating the self-absorption process of the activated source using the Monte Carlo method, including calculating the self-absorption correction factor and combining it with the initial gamma spectrum.
[0019] Furthermore, the geometric model of the activation source is meshed, including:
[0020] The type and size of the mesh are determined based on the geometry of the activation source, the distribution of spatial measurement points, and the requirements of the inversion algorithm.
[0021] Based on the type and size of the mesh, the geometric model of the activation source is meshed, so that the discretized three-dimensional activity distribution is determined by the vector P=[P1,P2,…,P…]. n ], where n is the number of grid cells.
[0022] Furthermore, when measuring gamma ray counts at multiple points in space, the number of detection points m is greater than the number of grid points n.
[0023] Furthermore, the three-dimensional spatial response function of the detector is calculated in flux form, including:
[0024] Based on the Monte Carlo method, the simulation is located inside the activation source. A unit intensity gamma point source at the detector location Photon flux density generated at the location The normalized three-dimensional spatial response function is calculated using the following formula:
[0025]
[0026] in, Let be the photon flux, and solve it using the Monte Carlo method; It is the total response of the entire radiation source to the detector, and V represents the volume fraction.
[0027] Furthermore, establishing the response equation system includes:
[0028] The detector count is represented as R = [R1,R2,…,R...]. m ], where m is the number of detection points;
[0029] Based on the aforementioned three-dimensional spatial response function, a system of equations is constructed:
[0030]
[0031] in, Indicates the location of the measuring point. At that time, the activation source's first The contribution of a photon generated in each grid to the detector count.
[0032] Furthermore, when solving the system of equations, m > n is required.
[0033] Furthermore, the specific process of calculating the three-dimensional spatial response function in flux form includes:
[0034] Establish a point source model, and assume an arbitrary position r of the spatial volume source. i There is an anisotropic gamma point source with a radiation intensity of 1. Where E represents energy. For the photon energy spectrum, For the Dirac function, Indicates the angle of the photon;
[0035] Define the detector response characteristics for locations outside the volume source. An isotropic gamma detector at a given location, with a detector sensitivity coefficient. ,in, This represents the gamma response cross section of the detector;
[0036] Get the location within the source The photons generated at the source location, for positions outside the source The detector's three-dimensional spatial response function at that location.
[0037]
[0038]
[0039]
[0040] Among them, the energy spectrum of the radioactive source and its location within the source With respect to photon detector type and location When all are known, C m It is a constant. Indicates that it is located at The radioactive source at the location is located The gamma detector count at the location, and These represent the differential elements for energy and angular direction, respectively.
[0041] Will Normalization
[0042] .
[0043] A computer device / apparatus / system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of a method for inverting the three-dimensional radioactivity intensity of an activated source based on gamma detector counting.
[0044] A computer-readable storage medium having a computer program / instructions thereon that, when executed by a processor, implements the steps of a method for inverting the three-dimensional radioactivity intensity of an activated source based on gamma detector counting.
[0045] The beneficial effects of this invention are as follows:
[0046] Compared with existing technologies, this invention effectively solves the problem of inaccurate source term evaluation due to the lack of neutron irradiation history information. This invention obtains the characteristic gamma spectrum of the activated source through high-purity germanium detector measurement and self-absorption correction; it uses the Monte Carlo method to accurately calculate the three-dimensional spatial response function; and finally, it achieves activity distribution inversion by solving the response equations. Compared with traditional forward calculation methods, this invention only requires gamma detector counting data to complete the inversion, completely avoiding reliance on difficult-to-obtain neutron irradiation history information. Attached Figure Description
[0047] Figure 1 Overall calculation process diagram;
[0048] Figure 2 Flowchart for obtaining the average gamma spectrum;
[0049] Figure 3 Schematic diagram of the measurement point locations during the gamma counting measurement phase;
[0050] Figure 4 Schematic diagram of radioactive source activity distribution and detector response. Detailed Implementation
[0051] The present invention will now be further described with reference to the accompanying drawings.
[0052] This invention relates to the field of radiation field calculation during the decommissioning process of nuclear facilities, aiming to solve the problem of determining the activity distribution of activated sources under conditions of unknown neutron irradiation history. The inversion method provided by this invention includes: obtaining the characteristic gamma spectrum of the activated source and photon counts at different spatial locations through detector measurements; meshing the source geometric model; obtaining the three-dimensional spatial response function of the detector using Monte Carlo simulation; and finally, achieving three-dimensional activity distribution inversion without neutron irradiation history information by solving the response equation set.
[0053] according to Figure 1 The present invention is implemented using the following technical solution: The characteristic gamma energy spectrum of the activation source is acquired and the spatial photon count is measured using a gamma detector; the three-dimensional spatial response function of the detector is obtained based on Monte Carlo calculations; and the three-dimensional activity distribution of the activation source is derived by solving the response equations. The specific steps are as follows:
[0054] Step 1: Using experimental measurements, the characteristic gamma spectrum of the activated source is obtained through detector measurements and simulation corrections, such as... Figure 2 As shown;
[0055] 1) Use a high-purity germanium detector to perform energy spectrum measurements on the activated source to obtain its initial gamma spectrum;
[0056] 2) Use the Monte Carlo method to establish a geometric model of the activation source, simulate its self-absorption process, and obtain the self-absorption correction factor;
[0057] 3) Combine the initial gamma spectrum with the self-absorption correction factor to obtain the corrected characteristic gamma spectrum.
[0058] Step 2: Perform appropriate mesh generation on the geometric model of the activation source;
[0059] 1) Based on the geometry of the activation source, the distribution of spatial measurement points, and the requirements of the inversion algorithm, determine the type and size of the mesh, and perform mesh generation on the geometric model of the activation source;
[0060] 2) The discretized three-dimensional activity distribution is represented by the vector P = [P1, P2, …, P n ] indicates that n is the number of grids, where each element of the vector corresponds to the activity value of a grid.
[0061] Step 3: Arrange multiple measuring points at different locations in space, and use a gamma detector to measure the gamma ray count generated by the activation source. The number of measuring points should be greater than the number of grid points (n) defined in Step 2. Record the spatial coordinates of each measuring point, such as... Figure 3 As shown.
[0062] Step 4: Based on the Monte Carlo method, construct the detector's response model to the activation source at different measurement points. Obtain the detector's three-dimensional spatial response function through forward Monte Carlo calculation, such as... Figure 4 As shown;
[0063] 1) Using the Monte Carlo method, the response model of the activation source at different measurement points on the detector is reconstructed. The gamma ray count at the detector can then be obtained using the Boltzmann equation:
[0064] (1)
[0065] In the formula, P(r) represents the radioactivity intensity at source location r, and w(r, r0) is... The three-dimensional spatial response function of the detector is given by V, which represents the volume of the radioactive source (i.e., the volume integral), C, which represents the sensitivity count of the detector, and dr, which represents the differential element.
[0066] In practice, P(r) is represented by the vector P through the discretized three-dimensional activity distribution grid from step two. During detector measurements, the three-dimensional spatial response function w(r) of the detector at that location needs to be calculated simultaneously. Its physical definition is the contribution of a photon generated at any location r of the radiation source to the detector count. Corresponding to the discretized data of the radiation source, w(r) is discretized as w = [w1, w2, ..., w...]. n ].
[0067] 2) The three-dimensional spatial response function of the detector is calculated based on the response model. To eliminate the ray effect, Monte Carlo calculation is used to obtain the three-dimensional spatial response function of the detector.
[0068] The calculation of the detector's three-dimensional spatial response function needs to start from the transport equation, assuming that at any position r of the space source... i There is an anisotropic gamma point source with a radiation intensity of "1", which can be represented as:
[0069] (2)
[0070] In the formula, E represents energy. For the photon energy spectrum, For the Dirac function, Indicates the angle of the photon.
[0071] For locations outside the body source The isotropic gamma detector at the location has a detector sensitivity coefficient given by formula (3):
[0072] (3)
[0073] In the formula, This represents the gamma response cross section of the detector.
[0074] Therefore, by combining formulas (1), (2), and (3), the location within the source can be obtained. The photons generated at the source location, for positions outside the source The response function of the detector at that location is:
[0075] (4)
[0076] (5)
[0077] In the formula, the energy spectrum of the radioactive source and the position within the source are... With respect to photon detector type and location Given that all are known, C m It is a constant.
[0078] Since the reading unit of a gamma detector is arbitrary, it can be... Normalization yields:
[0079] (6)
[0080] Furthermore, according to formula (1), the value located at... The radioactive source at the location is located The gamma detector count at that location can be expressed as:
[0081] (7)
[0082] In the formula, Indicates by Source strength reaches detector position Photon flux density at that location and These represent the differential elements for energy and angular direction, respectively.
[0083] Combining equations (6) and (7), we can obtain equation (8), which is the formula for calculating the three-dimensional spatial response function of the gamma detector in flux form.
[0084] (8)
[0085] In the formula, It is located in The point source is generated and arrives at. The detector response per unit volume generated by photons from that portion of the detector's sensitive volume. It is the total response of the entire radiation source to the detector.
[0086] It can be seen that as long as the photon flux can be obtained... The three-dimensional spatial response function of the gamma detector can then be obtained. . The solution can be obtained using the Monte Carlo method.
[0087] Step 5: Based on the three-dimensional spatial response function, establish a set of response equations between detector counts and activation source grid activity. By solving this set of equations, the three-dimensional activity distribution of the activation source can be obtained through inversion.
[0088] 1) Based on the response relationship between the three-dimensional activity distribution of the activation source and the detector count, a set of response equations between the three-dimensional activity distribution and the detector count is constructed using the obtained three-dimensional spatial response function of the detector. Assume there are m gamma counts at each detection point, and the detector count is represented as R = [R1, R2, …, R…]. m Then, the response equations between the three-dimensional activity distribution of the activation source and the detector count can be obtained through formula (1):
[0089] (6)
[0090] in, Indicates the location of the measuring point. At that time, the activation source's first The contribution of a photon generated in each grid to the detector count.
[0091] 2) After the response equation system is constructed, the three-dimensional activity distribution of the radioactive source can be obtained by solving the equation system. To ensure that the equation system is solvable, it is necessary to ensure that m > n.
[0092] In particular, in some preferred embodiments of the present invention, a computer device is also provided, including a memory and a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the three-dimensional radioactivity inversion method for activated sources based on gamma detector counting described in any of the above embodiments.
[0093] In some other preferred embodiments of the present invention, a computer-readable storage medium is also provided, on which a computer program / instruction is stored, wherein when the computer program is executed by a processor, the steps of the three-dimensional radioactivity intensity inversion method for activated sources based on gamma detector counting described in any of the above embodiments are implemented.
[0094] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above embodiments of the activation source three-dimensional radioactivity intensity inversion method based on gamma detector counting, which will not be repeated here.
[0095] Computer-readable storage media encompass a variety of types, including persistent and non-persistent, portable and fixed. These media store information using different technologies, and the content can be machine instructions, data structures, program modules, or other types of data. Some typical examples of computer storage media include: phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), various types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other storage technologies, optical storage media such as CD-ROM and digital video disc (DVD), magnetic storage devices such as magnetic tape and disks, and other non-transferable media used to store information accessible to computing devices. It is important to note that the computer-readable media described herein do not include temporary storage media, such as modulated data signals and carrier waves.
[0096] Those skilled in the art will further recognize that the operation of the module can be achieved using existing technical protocols or programs, without relying on new computer programs themselves. The units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.
[0097] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented in hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.
[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method of three-dimensional radioactivity intensity inversion of an activated source based on gamma detector counts, characterized in that, The method comprises the following steps: acquiring a characteristic gamma spectrum of the activated source, including measuring an initial gamma spectrum by a detector, and correcting a self-absorption effect based on a Monte Carlo simulation to obtain a corrected characteristic gamma spectrum; dividing a geometric model of the activated source into grids to discretize a three-dimensional activity distribution into a vector form; arranging multiple measuring points at different positions in space, measuring gamma ray counts generated by the activated source, and recording spatial coordinates of each measuring point; based on a Monte Carlo method, constructing a response model of the detector to the activated source at different measuring point positions, and calculating a three-dimensional spatial response function of the detector; based on the three-dimensional spatial response function, establishing a response equation set between detector counts and grid activities of the activated source, and solving the equation set to obtain the three-dimensional activity distribution of the activated source.
2. The method of claim 1, wherein, The initial gamma spectrum is measured by a high-purity germanium detector; the self-absorption effect correction is simulated by a Monte Carlo method to simulate the self-absorption process of the activated source, including calculating a self-absorption correction factor and combining it with the initial gamma spectrum.
3. The method of claim 1, wherein, The geometric model of the activated source is divided into grids, including: determining the type and size of the grid according to the geometric shape of the activated source, the distribution of the spatial measuring points, and the requirements of the inversion algorithm; based on the type and size of the mesh, meshing the geometric model of the activation source such that the discretized three-dimensional activity distribution is represented by vectors n is the number of meshes.
4. The method of claim 3, wherein the method is based on a three-dimensional radioactivity inversion of the source of activation using the counts of the gamma detector. When measuring the gamma ray counts at multiple measuring points in space, the number m of measuring points is greater than the number n of grids.
5. The method of claim 4, wherein the method is based on the inversion of the three-dimensional activity distribution from the gamma detector counts. The three-dimensional spatial response function of the detector is calculated in flux form, including: Based on the Monte Carlo method, the photon flux density generated by a unit strength gamma point source located at an internal position of the activation source at a detector position is simulated Based on the Monte Carlo method, the photon flux density generated by a unit strength gamma point source located at an internal position of the activation source at a detector position is simulated Based on the Monte Carlo method, the photon flux density generated by a unit strength gamma point source located at an internal position of the activation source at a detector position is simulated and the normalized three-dimensional spatial response function is calculated by the following equation, wherein, is the photon flux and is solved by the Monte Carlo method; is the total response of the entire source to the detector, V denotes the volume integral.
6. The method of claim 5, wherein the method is a three-dimensional radioactivity inversion method based on the gamma detector counts of the activated source. The establishment of the response equation set includes: The detector count is represented as R = [R1,R2,…,R...]. m ], where m is the number of detection points; based on the three-dimensional spatial response function, constructing an equation set: wherein, represents the contribution to the detector count of a photon generated in the i-th grid of the activation source at the position of the measurement point at time t. .
7. The method of claim 6, wherein the method is a three-dimensional radioactivity inversion method based on the gamma detector counts of the activated source, characterized in that, When solving the equation set, it is required that m > n.
8. The method of claim 5, wherein the method is a three-dimensional radioactivity inversion method based on the gamma detector counts. The specific process of calculating the three-dimensional spatial response function in flux form includes: A point source model is established, which is set at any position of a spatial volume source with an anisotropic gamma point source with a source intensity of 1 wherein E represents energy, is a photon energy spectrum, is a Dirac function, represents the angle of the photon; Defining the detector response characteristics for isotropic gamma detectors located at positions outside the volume source wherein the detector sensitivity coefficient wherein, is the gamma reaction cross section of the detector; obtaining photons generated at an in-source location a three-dimensional spatial response function of the detector for an out-of-source location wherein, at the source spectrum, the source-in-position and the photon detector type and position are known, C m is a constant, represents the count of a radioactive source located at by a gamma detector located at and and represent the energy and angular direction differentials, respectively; Will normalization, 。 9. A computer apparatus / device / system comprising a memory, a processor, and a computer program stored on the memory, characterized in that: The processor executes the computer program to implement the steps of the method of any one of claims 1 to 8.
10. A computer readable storage medium having stored thereon computer programs / instructions, characterized in that: The computer program / instructions are executed by the processor to implement the steps of the method of any one of claims 1 to 8.