A spent fuel rack neutron absorption panel boron-10 areal density inspection probe and method

Abstract

This invention relates to the field of aging assessment of neutron-absorbing materials in spent fuel of nuclear power plants, and in particular to a probe and method for checking boron concentration in neutron-absorbing panels of spent fuel grids. The probe includes a connecting assembly, a source probe, and a detection probe. The source probe and detection probe are installed at the end of the connecting assembly. Neutron-absorbing panels are arranged around the perimeter of the spent fuel grid, and the connecting assembly places the source probe and detection probe in adjacent spent fuel grids. This invention is based on the neutron transmission method. A neutron source is set in the source probe, and the detection probe counts the neutrons that pass through the neutron-absorbing panel, thereby calculating the surface density of neutron poison in the neutron-absorbing panel. Compared to the traditional method of indirectly assessing the surface density of neutron poison through hanging plates, the solution provided by this invention can achieve online and real-time measurement of the surface density of neutron poison in any grid, any neutron-absorbing panel, and at any height in the spent fuel pool.

Description

Technical Field

[0001] This invention relates to the field of aging assessment of neutron-absorbing materials in spent nuclear power plant fuel, and in particular to a probe and method for checking the boron 10 areal density of a spent fuel grid neutron-absorbing panel. Background Technology

[0002] Spent fuel assembly storage racks are the core equipment of a nuclear power plant's spent fuel storage system, primarily used for storing fuel assemblies unloaded from the nuclear reactor. To achieve safe and reliable high-density storage, neutron-absorbing panels containing neutron-absorbing materials (such as boron, samarium, and cadmium) are typically arranged in the storage racks to absorb neutrons generated by spent fuel fission, ensuring the critical safety of the spent fuel pool.

[0003] Since neutron-absorbing materials are a critical component in ensuring the criticality safety of fuel storage racks, regular in-service inspections of neutron absorbers in spent fuel storage racks are required by nuclear safety authorities to verify their effectiveness. Currently, domestic nuclear power plants use a method of suspending test samples and conducting periodic random inspections. For example, CN209343788U designs a neutron-absorbing material test sample suspension device; CN117238542A proposes a method for assessing the aging status of spent fuel neutron absorber materials. This method involves removing the sample for testing to determine the content of neutron-absorbing poisons in the sample, confirming whether it meets design requirements and can continue to function within its design lifespan. This allows for an assessment of whether the fuel rack needs to be replaced or repaired to ensure the safety and reliability of fuel storage.

[0004] However, the existing technology for evaluating the effectiveness of neutron absorbing materials using hanging plates has certain shortcomings: First, it requires the development of a monitoring plan in advance and the hanging of a sufficient number of hanging plates in the spent fuel pool; second, the hanging plates need to be removed and sent for testing periodically, which involves a large workload; third, in the spent fuel pool, specimens are only arranged in typical areas to obtain indirect representative values ​​of the toxic content in the neutron absorbing panels within that area, and it is not possible to directly measure the areal density of the neutron absorbing material. Summary of the Invention

[0005] This invention provides a probe and method for checking the boron 10 areal density of a neutron absorbing panel in a spent fuel grid, which solves the problems of existing methods for evaluating the effectiveness of neutron absorbing materials using hanging plates, such as large quantity, heavy workload, and inability to directly measure the areal density of neutron absorbing materials.

[0006] The technical solution of the present invention is as follows: This invention proposes a probe for checking the boron 10 areal density of a neutron absorption panel in a spent fuel grid. The probe includes a connecting assembly, a source probe, and a detection probe. The source probe and the detection probe are installed at the end of the connecting assembly. Neutron absorption panels are arranged around the perimeter of the spent fuel grid. The connecting assembly places the source probe and the detection probe in adjacent spent fuel grids.

[0007] In some embodiments, the connecting assembly includes two rod-shaped structures. A source probe is installed at the end of one rod-shaped structure of the connecting assembly, and a detection probe is installed at the end of the other rod-shaped structure of the connecting assembly. The source probe and the detection probe are arranged in parallel. The connecting assembly has a length adjustment function to adjust the distance between the source probe and the detection probe.

[0008] In some embodiments, the probe is further provided with a source-taking fixture for mounting a neutron source on the source probe or removing a neutron source from the source probe.

[0009] In some embodiments, the source probe includes a probe housing, a source detector moderator, a front-side moderator, a neutron source, and a collimating aperture. A neutron source mounting position is provided inside the probe housing. The neutron source is positioned and placed inside the source probe using a source-taking fixture. The source detector moderator is fitted around the neutron source, enclosing the neutron source in directions other than the measurement direction. The source detector moderator slows down fast neutrons outside the measurement direction into thermal neutrons and scatters them in the measurement direction. The front-side moderator is attached to the front end face of the neutron source directly facing the measurement direction. The front-side moderator slows down fast neutrons in the measurement direction of the neutron source. The collimating aperture is located at the center of the front-side moderator and is coaxially aligned with the measurement direction of the emitted neutrons from the neutron source. The source detector moderator, the front-side moderator, the neutron source, and the collimating aperture are encapsulated within the probe housing.

[0010] In some embodiments, the detector probe includes a neutron detector, a neutron absorber, a neutron shield, and a probe housing. The neutron detector is arranged in an array and is positioned on one side near the neutron source measurement direction of the source probe. The neutron absorber is positioned outside the neutron detector and is used to absorb neutrons. The neutron shield is positioned outside the neutron absorber and is used to prevent the scattering counting effect generated by the slowing down of some fast neutrons on the neutron source side on the detector side. The neutron detector, neutron absorber, and neutron shield are encapsulated in the probe housing.

[0011] In some embodiments, the neutron detector is equipped with four probes. The neutron detector is used to count thermal neutrons that pass through the neutron absorption panel and reach the detector. The neutron detector is connected to the back-end processing circuitry via a cable.

[0012] In some embodiments, the neutron source is 252Cf and Am-Be, the source detector moderator is a polyethylene moderator, and the collimation aperture is a trapezoidal aperture structure; the neutron detector is a He3 neutron detector or a BF3 neutron detector, and the size of the detector probe is the same as the size of the source probe.

[0013] This invention proposes a method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel lattice, the method comprising: Step 1: Install the source probe and detector probe onto the connection assembly; Step 2: Install the neutron source onto the source probe using the source-taking fixture and tighten it. Step 3: Measure the surface density of the poison on the neutron absorption panel.

[0014] In some embodiments, during step one, the neutron detector cable of the detector probe is connected to an external processing circuit when installing the source probe and the detector probe.

[0015] In some embodiments, step three specifically includes: Step 3.1: Use a field crane to hoist the connecting assembly for the dual probes onto the grid of the target to be tested. Use a field crane to place the source probe and the detector probe into the target grid. Place the neutron absorption panel to be tested between the source probe and the detector probe. Step 3.2: Raise the probe according to the preset step size and speed, read the count value of the neutron detector through the back-end processing circuit, and install to calculate the surface density.

[0016] The implementation of this invention has the following beneficial effects: 1. This invention proposes a probe and method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel trough. Based on the neutron transmission method, a neutron source is placed in the source probe. The probe counts the neutrons that pass through the neutron-absorbing panel, thereby calculating the areal density of the neutron poison in the neutron-absorbing panel. Compared to the traditional method of indirectly assessing the areal density of neutron poison using a plate, the solution provided by this invention can achieve online, real-time measurement of the areal density of neutron poison in any trough, any neutron-absorbing panel, and at any height in a spent fuel pool.

[0017] 2. This invention proposes a probe and method for checking the boron 10 areal density of the neutron absorbing panel in a spent fuel grid. The source probe and detection probe are designed according to the dimensions of the spent fuel grid in a nuclear power plant. The spacing between the source probe and detection probe is adjusted by mounting holes on the connecting assembly, making it suitable for the testing needs of spent fuel grids of different sizes and spacings. The neutron source in the source probe is a detachable structure, which can be recovered in a special container after testing, ensuring the management and control requirements of the neutron source and the radiation safety of personnel. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a boron 10 areal density testing probe for a neutron absorption panel in a spent fuel grid, as proposed in an embodiment of the present invention. Figure 2 This is a schematic diagram of the installation of a boron 10 areal density testing probe for a neutron absorption panel in a spent fuel grid, as proposed in an embodiment of the present invention. Explanation of reference numerals in the attached drawings: 1. Connecting assembly; 2. Source acquisition fixture; 3. Source probe; 4. Detection probe; 31. Source probe housing; 32. Source detector moderator; 33. Source front moderator; 34. Neutron source; 35. Collimation aperture; 41. Neutron detector; 42. Neutron absorber; 43. Neutron shield; 44. Detection probe housing; 5. Neutron absorption panel. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figures 1 to 2 As shown, the present invention proposes a probe and method for checking the boron 10 areal density of a neutron absorption panel in a spent fuel grid. The probe includes a connecting assembly 1, a source sampling fixture 2, a source probe 3, and a detection probe 4.

[0021] A source probe and a detection probe are installed at the end of the connecting assembly 1. The connecting assembly 1 includes two rod-like structures. The source probe is installed at the end of one rod-like structure, and the detection probe is installed at the end of the other rod-like structure. The source probe and the detection probe are arranged in parallel. This invention connects to the source probe and the detection probe through the connecting assembly 1. By driving the connecting assembly 1, the detection probe moves along the height direction of the neutron absorption panel 5 at a preset speed and height for detection. The connecting assembly 1 has an adjustment function, which can adjust the distance between the source probe and the detection probe to meet the spacing requirements of different types of spent fuel grids. The connecting assembly 1 is spliced ​​together by connecting rods of different lengths, which can be used for the detection needs of grids of different heights.

[0022] like Figure 2 As shown, neutron absorption panels 5 are arranged around the grid, and source probe 3 and detection probe 4 each occupy one grid so that neutrons can penetrate through the neutron absorption panels 5 for detection.

[0023] The source probe is used to slow down the fast neutrons generated by the neutron source into thermal neutrons. After passing through the neutron absorption plate, the thermal neutrons enter the detection unit for counting, thereby realizing the measurement of the surface density of the neutron poison. The source probe includes a probe housing, a source detector moderator 32, a front-side moderator, a neutron source 34, and a collimation aperture 35. The neutron source 34 is mounted inside the probe housing and positioned within the probe using a source-taking fixture 2. The source detector moderator 32 is positioned around the neutron source 34, enclosing it in the non-measurement direction. The source detector moderator 32 slows down fast neutrons outside the measurement direction into thermal neutrons and scatters them in the measurement direction, increasing the number of thermal neutrons in that direction. The front-side moderator is close to the front face of the neutron source 34 facing the measurement direction. It slows down fast neutrons in the measurement direction, further increasing the total number of thermal neutrons in that direction. The collimation aperture 35 is located at the center of the front-side moderator and is coaxially aligned with the measurement direction of the emitted neutrons from the neutron source 34, forming a directional neutron passage. The collimation aperture 35 reduces the influence of neutrons from other directions and expands the detector's three-dimensional measurement range. The source detector moderator 32, the source front moderator 33, the neutron source 34, the collimating aperture 35, and other components are all encapsulated in the probe housing, which is connected to the outside via the connecting assembly 1. The trapezoidal collimating aperture 35 has a height that covers the height of the neutron detector 41, and a solid angle that covers the detection range of the neutron detector 41.

[0024] Neutron Source 34 can be used 252 The Cf and Am-Be neutron sources 34 are installed, removed, and replaced using the source-taking fixture 2. When the equipment is in use, the neutron source 34 tube and neutron source 34 are inserted into the source assembly using the source-taking fixture 2. When the equipment is not in use, the neutron source 34 tube and neutron source 34 are removed using the source-taking fixture 2 and stored in a suitable shielding device and source library to ensure the management and control of the neutron source 34 and the radiation safety of personnel. The source probe contains a high-density polyethylene moderator to slow down and scatter fast neutrons in the non-measurement direction towards the measurement direction, while simultaneously slowing down fast neutrons in the measurement direction, further increasing the total number of thermal neutrons in the measurement direction. The source probe's dimensions are designed according to the grid size, compatible with both quadrilateral and hexagonal grids for detection. The source probe is connected to the connection assembly 1 through mounting holes on the housing.

[0025] like Figure 2As shown, the detector probe includes a neutron detector 41, a neutron absorber 42, a neutron shield 43, and a probe housing 44. The neutron detector 41 is arranged in an array, positioned on one side of the neutron source 34 near the source probe, in the measurement direction. All four probes of the neutron detector 41 simultaneously measure and count thermal neutrons that pass through the neutron absorption panel 5 and reach the detector. The neutron detector 41 is connected to the back-end processing circuitry via cables. The neutron absorber 42 is located outside the neutron detector 41 and is used to absorb neutrons. The neutron shield 43 is located outside the neutron absorber 42 and is used to prevent the scattering counting effect caused by the slowing down of some fast neutrons from the source side at the detector side. The neutron detector 41, neutron absorber 42, and neutron shield 43 are all encapsulated within the probe housing 44, which is connected to the outside via a connecting assembly 1.

[0026] The detection probe is used to count the thermal neutrons that pass through the neutron-absorbing panel 5 and reach the detector. The change in transmittance reflects the change in the surface density of the poison in the neutron-absorbing panel. The probe can use He3, BF3, or other neutron detectors 41 as detection sensors to count the thermal neutrons after passing through the neutron-absorbing panel 5. Four neutron detectors 41 are arranged in an array along the transverse direction of the neutron-absorbing panel 5 to measure the surface density of different areas of the neutron-absorbing panel 5. The signals from the neutron detectors 41 are transmitted to the signal processing unit at the back end via connecting cables. A neutron shield 43 is installed in the detection probe to shield against interference caused by the scattering counting effect. The size of the detection probe is the same as that of the source probe, and it is connected to the connecting assembly 1 through mounting holes on the outer shell.

[0027] After the neutron source 34 is installed, the in-situ detection probe is transported to the designated detection surface of the designated grid. Part of the neutrons emitted by the source probe are absorbed by the neutron absorption panel 5, and the other part is captured by the neutron detector 41 in the detection probe 4. By comparing the count with the zero-dose plate (standard plate), the surface density of the poison in the neutron absorption panel 5 of the current detection object can be evaluated and calculated.

[0028] The neutron absorber 42 areal density detection probe of the present invention consists of a source probe, a detector probe, and a connecting assembly 1. The working principle of the detection probe is as follows: Figure 1 As shown, the details are as follows: A thermal neutron of intensity I0 passes through neutron-absorbing panel 5, and is partially absorbed, with the unabsorbed portion having intensity I. Based on the exponential decay law of radiation in matter, I0, I, and the surface density of the neutron-absorbing poison have the following relationships, as shown in Equations 1 to 3: Formula 1 Formula 2 Formula 3 Where I is the thermal neutron intensity after passing through the neutron absorber; I0 is the thermal neutron intensity before passing through the neutron absorber; u m ρ is the mass attenuation coefficient of the neutron absorber for thermal neutrons. s is the surface density of the neutron-absorbing poison; T is the neutron transmittance; k is a constant.

[0029] After calibrating the coefficients in the above formula using an unused, standard neutron absorbing panel 5 with a known surface density, the actual neutron absorbing panel 5 can be measured.

[0030] This invention proposes a method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel lattice, the method comprising: Step 1: Install the source probe and detector probe on the connection assembly 1; install the source probe and detector probe on the connection assembly 1, and connect the neutron detector 41 cable to the external processing circuit.

[0031] Step 2: Install the neutron source 34 onto the source probe using the source tooling 2 and tighten it.

[0032] Step 3: Measure the surface density of the poison on neutron absorption panel 5.

[0033] Step 3.1: Use a field crane to hoist the connecting assembly 1 that connects the dual probes to the top of the target grid frame, use a field crane to place the source probe and detector probe inside the target grid frame, and place the neutron absorption panel 5 to be tested between the source probe and the detector probe; Step 3.2: Raise the probe according to the preset step size and speed, read the count value of the neutron detector 41 through the back-end processing circuit, and calculate the surface density.

[0034] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A spent fuel rack neutron absorption panel boron- 10 areal density inspection probe characterized by, The probe includes a connection assembly (1), a source probe and a detection probe. The source probe and the detection probe are installed at the end of the connection assembly (1). Neutron absorption panels (5) are arranged around the spent fuel grid. The connection assembly (1) places the source probe and the detection probe in an adjacent spent fuel grid.

2. The spent fuel rack neutron absorber panel boron- 10 areal density inspection probe of claim 1, wherein, The connecting component (1) includes two rod-shaped structures. A source probe is installed at the end of one rod-shaped structure of the connecting component (1), and a detection probe is installed at the end of the other rod-shaped structure of the connecting component (1). The source probe and the detection probe are arranged in parallel. The connecting component (1) has a length adjustment function to adjust the distance between the source probe and the detection probe.

3. The spent fuel rack neutron absorber panel boron- 10 areal density inspection probe of claim 1, wherein, The probe is also provided with a source acquisition tool (2), which is used to install the neutron source (34) on the source probe or to remove the neutron source (34) from the source probe.

4. The spent fuel rack neutron absorber panel boron- 10 areal density inspection probe of claim 3, wherein, The source probe includes a probe housing, a source detector moderator (32), a source front moderator, a neutron source (34), and a collimation aperture (35). The probe housing contains a mounting position for the neutron source (34). The neutron source (34) is positioned and placed inside the source probe using a source-taking fixture (2). The source detector moderator (32) is positioned and arranged around the neutron source (34), enclosing the neutron source (34) in the non-measurement direction. The source detector moderator (32) will block fast-moving neutrons outside the measurement direction. The neutrons are slowed down into thermal neutrons and scattered in the measurement direction; the source front slower is close to the front end of the neutron source (34) facing the measurement direction, and the source front slower is used to slow down the fast neutrons in the measurement direction of the neutron source (34); the collimation hole (35) is opened at the center of the source front slower and is coaxially aligned with the measurement direction of the neutron emitted by the neutron source (34); the source detector slower (32), the source front slower, the neutron source (34) and the collimation hole (35) are encapsulated in the probe shell.

5. A boron 10 areal density testing probe for a spent fuel grid neutron absorption panel (5) according to claim 4, characterized in that, The detector probe includes a neutron detector (41), a neutron absorber (42), a neutron shield (43), and a probe housing (44). The neutron detector (41) is arranged in an array and is located on one side of the neutron source (34) near the source probe in the measurement direction. The neutron absorber (42) is located outside the neutron detector (41) and is used to absorb neutrons. The neutron shield (43) is located outside the neutron absorber (42) and is used to prevent the scattering counting effect generated by some fast neutrons on the neutron source (34) side after slowing down on the detector side. The neutron detector (41), neutron absorber (42), and neutron shield (43) are encapsulated in the probe housing (44).

6. The probe for checking the boron 10 areal density of a spent fuel grid neutron absorption panel according to claim 5, characterized in that, The neutron detector (41) is equipped with four probes. The neutron detector (41) is used to count thermal neutrons that pass through the neutron absorption panel (5) and reach the detector. The neutron detector (41) is connected to the back-end processing circuit via a cable.

7. The probe for checking the boron 10 areal density of a spent fuel grid neutron absorption panel according to claim 6, characterized in that, The neutron source (34) uses 252Cf and Am-Be, the source detector moderator (32) is a polyethylene moderator, and the collimation aperture (35) is a trapezoidal aperture structure; the neutron detector (41) uses a He3 neutron detector (41) or a BF3 neutron detector (41), and the size of the detector probe is the same as the size of the source probe.

8. A method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel grid, wherein the method uses the probe described in any one of claims 1-7, characterized in that, The method includes: Step 1: Install the source probe and detector probe onto the connection assembly (1); Step 2: Install the neutron source (34) onto the source probe using the source sampling fixture (2) and tighten it; Step 3: Measure the surface density of the poison on the neutron absorption panel (5).

9. A method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel grid according to claim 8, characterized in that, In step one, when installing the source probe and the detector probe, the neutron detector (41) cable of the detector probe is connected to the external processing circuit.

10. A method for checking the boron 10 areal density of a neutron-absorbing panel in a spent fuel grid according to claim 8, characterized in that, Step three specifically includes: Step 3.1: Use a field crane to hoist the connecting assembly (1) that connects the dual probes to the top of the grid frame to be tested. Use a field crane to place the source probe and the detector probe inside the grid frame. Place the neutron absorption panel (5) to be tested between the source probe and the detector probe. Step 3.2: Raise the probe according to the preset step size and speed, read the count value of the neutron detector (41) through the back-end processing circuit, and install the calculation surface density.

Images