Design method and system of self-powered neutron detector with high sensitivity and consistency

Abstract

The present invention discloses a design method and system of a highly sensitive and consistent self-powered neutron detector, including: establishing a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector; considering the space charge effect of the insulating layer, performing fine numerical simulation calculations of the self-powered neutron detector; obtaining the optimal detector structure size that meets the initial thermal neutron sensitivity requirements according to the design requirements of the core measurement system; determining the key influencing factors that affect the initial thermal neutron sensitivity and consistency of the self-powered neutron detector, analyzing their influence on the initial thermal neutron sensitivity of the detector, and obtaining the maximum allowable tolerance of the key influencing factors within the range allowed by the consistency; using the self-powered neutron detector burnup layering calculation method and fA-level micro-current signal processing technology to further determine the burnup life of the self-powered neutron detector. The present invention theoretically solves the problems of low thermal neutron sensitivity, poor consistency and frequent replacement of existing self-powered neutron detectors.

Description

Technical Field

[0001] The present invention relates to the technical field of self-powered neutron detector design, and in particular to a design method and system for a long-life self-powered neutron detector with high sensitivity and consistency. Background Art

[0002] Self-sufficient neutron detectors are an important part of the core measurement system. At present, my country has realized the localization of a full set of signal processing equipment for the core measurement system of the third-generation nuclear power reactor. However, the self-sufficient neutron detectors used in domestic nuclear power plants are all imported. In the current volatile international environment, there is a risk of sales ban at any time, and at this stage, imported detectors still have shortcomings such as low service life and frequent replacement. These technical bottlenecks have greatly restricted my country's technical improvement in the field of core key parameter measurement in nuclear energy systems. In addition, the refueling cycle of the Hualong One nuclear power plant is 18 months, while the service life of imported self-sufficient neutron detectors is 48 months, which is between two refueling cycles and three refueling cycles. As a result, the detector must be replaced after two refueling cycles (36 months), wasting the remaining 12 months of the detector's service life, and the actual use efficiency of the detector is low. In addition, the self-sufficient neutron detectors currently developed in China face the problem of poor consistency when mass-produced, with a consistency deviation of ±(1~2)%, which cannot meet the requirements of the core neutron flux measurement system.

[0003] Therefore, the current domestically produced self-sufficient neutron detectors have problems such as low thermal neutron sensitivity, poor consistency and the need for frequent replacement. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the current domestic self-powered neutron detectors have the problems of low thermal neutron sensitivity, poor consistency and need for frequent replacement. The purpose of the present invention is to provide a design method and system for a self-powered neutron detector with high sensitivity and consistency, to provide systematic guidance for the design of a self-powered neutron detector (SPND), to achieve the design of a long-life self-powered neutron detector with high sensitivity and high consistency in theoretical design, and to guide the production and manufacturing of the detector, process control, detector (component) life assessment and component replacement plan design. Thus, the problems of low thermal neutron sensitivity, poor consistency and need for frequent replacement are solved.

[0005] The present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for designing a self-powered neutron detector with high sensitivity and consistency, the method comprising:

[0007] Step 1, by simulating the process of space charge in the insulating layer of the self-powered neutron detector from zero to steady state, a calculation model of space charge effect of the insulating layer of the self-powered neutron detector is established to obtain the space charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in steady state;

[0008] Step 2, based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, taking into account the space charge effect of the insulating layer, a fine numerical simulation calculation of the self-powered neutron detector is performed;

[0009] Step 3, according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector, obtaining the optimal detector structure size that meets the initial thermal neutron sensitivity requirements of the self-powered neutron detector;

[0010] Step 4, based on the optimal detector structure size, analyze the influence of changes in detector material parameters and geometric structure on the initial thermal neutron sensitivity of the self-powered neutron detector, and determine the key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector;

[0011] Step 5, analyzing the influence of key influencing factors on the initial thermal neutron sensitivity of the detector, and using a Monte Carlo simulation program within the range allowed by the consistency of the self-powered neutron detector to obtain the maximum allowable tolerance of the key influencing factors;

[0012] Step 6, using the self-powered neutron detector burnup layering calculation method and fA-level micro-current signal processing technology to further accurately determine the burnup life of the self-powered neutron detector and improve the signal-to-noise ratio of the detector output signal.

[0013] Furthermore, the method further comprises:

[0014] Based on the established relationship between the mechanical properties of the shell material of the self-powered neutron detector assembly and time in a typical pressurized water reactor operating environment, the mechanical properties of the shell of the self-powered neutron detector assembly at the end of the projectile burnup life are determined, and the service life of the shell of the self-powered neutron detector assembly is obtained;

[0015] The self-powered neutron detector assembly has a plurality of self-powered neutron detectors of the same size arranged in the axial direction.

[0016] Furthermore, step 1 includes the following sub-steps:

[0017] Step 11, using Monte Carlo software to establish a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector, using the neutron-photon source at the location of the self-powered neutron detector as the input of GEANT4, performing neutron-photon-electron coupled particle transport, and calculating the charge deposition rate distribution V in the insulating layer q (r,t);

[0018] Step 12, set the time step △t, take the charge deposition rate distribution and charge loss rate distribution at the previous moment in a single time step as the initial value at the current moment, and assume that the charge deposition rate and charge loss rate change linearly in a single time step, perform self-balancing calculation to obtain the stable charge distribution Q(r,t) at the current moment;

[0019] Step 13: Divide the charge distribution Q(r, t) by the volume of the insulating layer to obtain the charge density distribution ρ(r, t); and further obtain the potential distribution of the insulating layer according to the Poisson equation

[0020] Step 14: Based on the potential distribution of the insulating layer Further obtain the electric field distribution in the insulating layer and the current density distribution in the insulation layer

[0021] Step 15, according to the current density distribution and the surface area S(r) of the insulating layer, the new charge loss rate distribution V is calculated q,out (r,t);

[0022] Step 16, when the charge loss rate distribution obtained from two consecutive calculations is less than the convergence residual of the self-balancing iterative calculation, the self-balancing iterative calculation converges; otherwise, repeat steps 11 to 15;

[0023] Step 17, if the net charge deposition rate calculated at the current moment is less than the convergence residual of the global equilibrium iterative calculation, the global equilibrium iterative calculation converges, and the spatial charge, potential, and electric field distribution in the insulating layer of the self-powered neutron detector in the steady state are obtained; otherwise, repeat steps 11 to 16.

[0024] Furthermore, step 2 includes:

[0025] Step 21, based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, further construct a fine numerical simulation calculation model of the self-powered neutron detector;

[0026] Step 22, inputting the spatial charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in steady state into the fine numerical simulation calculation model of the self-powered neutron detector, accurately reconstructing the spatial electric field in the insulating layer of the self-powered neutron detector, and performing fine numerical simulation calculation of the self-powered neutron detector, further improving the accuracy of the simulation calculation of the self-powered neutron detector (SPND);

[0027] Among them, the detailed numerical simulation calculation model of the self-powered neutron detector is formed by adding the electromagnetic field interaction process to PhysicsList.cc of GEANT4.

[0028] Further, step 3 includes:

[0029] Step 31, according to the design requirements of the core measurement system, obtain the number N of self-powered neutron detectors distributed axially in the self-powered neutron detector assembly, the length L of a single self-powered neutron detector, and the maximum outer diameter R of a single self-powered neutron detector;

[0030] Step 32, using the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and the fine numerical simulation calculation model of the self-powered neutron detector, optimize the structural size of the self-powered neutron detector to ensure the highest initial thermal neutron sensitivity, and obtain the optimal detector structural size that meets the highest initial thermal neutron sensitivity requirement of the self-powered neutron detector.

[0031] Furthermore, the optimal detector structure dimensions include the collector thickness at the optimal initial thermal neutron sensitivity, the insulating layer thickness at the optimal initial thermal neutron sensitivity, and the emitter size at the optimal initial thermal neutron sensitivity.

[0032] Further, step 4 includes:

[0033] Step 41, analyzing the factors affecting the initial thermal neutron sensitivity and consistency of the detector by the material parameters and geometric structure of the detector according to the optimal detector structure size;

[0034] Step 42, adopting a single control variable method and using a Monte Carlo simulation program to analyze the influence of changes in influencing factors on the initial thermal neutron sensitivity of the detector, and determine the key influencing factors that affect the initial thermal neutron sensitivity of the self-powered neutron detector.

[0035] Furthermore, the influencing factors include emitter impurity elements and content, emitter purity, emitter density, emitter length, emitter radius, emitter thickness uniformity, insulating layer impurity element composition and content, insulating layer purity, insulating layer density, insulating layer thickness, collector impurity elements and content, collector purity, collector density, collector thickness, etc.

[0036] Furthermore, step 6 includes the following sub-steps:

[0037] Step 61, using a self-powered neutron detector burnup layering calculation method to obtain a relationship between the burnup of the emitter and time, and obtain the burnup life of the self-powered neutron detector;

[0038] Step 62, adopting fA-level micro-current signal processing technology to expand the measurement lower limit of the micro-current signal and improve the signal-to-noise ratio of the detector output signal.

[0039] In a second aspect, the present invention provides a highly sensitive and consistent self-powered neutron detector design system, which uses the highly sensitive and consistent self-powered neutron detector design method described above; the system comprises:

[0040] A calculation model building unit is used to build a calculation model of the space charge effect of the insulation layer of the self-powered neutron detector by simulating the process of the space charge in the insulation layer of the self-powered neutron detector from nothing to something and then to a steady state, so as to obtain the space charge, potential and electric field distribution in the insulation layer of the self-powered neutron detector in a steady state;

[0041] A fine calculation model building unit is used to perform fine numerical simulation calculations of the self-powered neutron detector based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and taking into account the space charge effect of the insulating layer;

[0042] An optimal structural dimension obtaining unit is used to obtain an optimal detector structural dimension that meets the initial thermal neutron sensitivity requirement of the self-powered neutron detector according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector;

[0043] A key influencing factor determination unit is used to analyze the influence of changes in detector material parameters and geometric structure on the initial thermal neutron sensitivity of the self-powered neutron detector based on the optimal detector structure size, and determine the key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector;

[0044] The maximum allowable tolerance analysis unit is used to analyze the impact of key influencing factors on the initial thermal neutron sensitivity of the detector. Within the range allowed by the consistency of the self-powered neutron detector, the maximum allowable tolerance of the key influencing factors is obtained by using the Monte Carlo simulation program;

[0045] The burnup life determination unit is used to further accurately determine the burnup life of the self-powered neutron detector by using the burnup layering calculation method of the self-powered neutron detector and the fA-level micro-current signal processing technology, and improve the signal-to-noise ratio of the detector output signal;

[0046] The service life determination unit is used to determine the mechanical properties of the shell of the self-powered neutron detector assembly at the end of the projectile burnup life according to the established relationship between the mechanical properties of the shell material of the self-powered neutron detector assembly and time in a typical pressurized water reactor operating environment, so as to obtain the service life of the shell of the self-powered neutron detector assembly; wherein the self-powered neutron detector assembly arranges a plurality of self-powered neutron detectors of the same size in the axial direction.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0048] The invention discloses a method and system for designing a self-powered neutron detector with high sensitivity and consistency. The new method proposed in the invention ensures the high sensitivity and consistency of the SPND detector from the design level, and guarantees the long life of the SPND detector and the detector assembly, which is of great significance for the manufacture of the SPND detector and the assembly. The invention can provide systematic guidance for the design of self-powered neutron detectors, realize the design of self-powered neutron detectors with high sensitivity and high consistency and long life in theoretical design, and guide the production and manufacturing of detectors and process control, detector (assembly) life assessment and assembly replacement scheme design. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0050] Figure 1 A flow chart of the design method of a highly sensitive and consistent self-powered neutron detector of the present invention;

[0051] Figure 2 Schematic diagram of the relationship between the charge change rate (net deposition rate, deposition rate and loss rate) in the Rh-SPND insulating layer of the present invention and time;

[0052] Figure 3 Schematic diagram of charge density at different times in the Rh-SPND insulating layer of the present invention;

[0053] Figure 4 Schematic diagram of potential distribution in the Rh-SPND insulation layer at different times of the present invention;

[0054] Figure 5 Schematic diagram of the electric field distribution in the Rh-SPND insulation layer at different times of the present invention;

[0055] Figure 6 This is a schematic diagram of the relationship between the initial thermal neutron sensitivity of the SPND detector of the present invention and the length of the emitter;

[0056] Figure 7 Schematic diagram of the relationship between the initial thermal neutron sensitivity of the SPND detector of the present invention and the radius of the emitter;

[0057] Figure 8 Schematic diagram of the relationship between the initial thermal neutron sensitivity of the SPND detector of the present invention and the thickness of the insulating layer;

[0058] Fig. 9 This is a comparison chart of the burnup analysis results of the SPND detector of the present invention;

[0059] Fig.10 This is a schematic diagram of the nanohardness variation trend of 316L stainless steel after irradiation according to the present invention;

[0060] Fig.11 A system structure block diagram is designed for the self-powered neutron detector with high sensitivity and consistency of the present invention. DETAILED DESCRIPTION

[0061] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0062] In view of the problems of low thermal neutron sensitivity, poor consistency and frequent replacement of domestic self-sufficient neutron detectors, the present invention designs a design method and system for self-sufficient neutron detectors with high sensitivity and consistency. The key factors affecting the performance of self-sufficient neutron detectors mainly include initial thermal neutron sensitivity, consistency and service life (including burnup life and service life). (1) Regarding the initial thermal neutron sensitivity of the self-sufficient neutron detector: on the one hand, the detector is finely modeled by using Monte Carlo simulation software to accurately track the source of the detector output current; on the other hand, by studying the influence of the size structure of different emitters, insulating materials, and collector materials on the detector output signal, the high sensitivity design of the detector is achieved under the premise of meeting the engineering design requirements. (2) Regarding consistency: by analyzing the sensitivity consistency verification mechanism of self-sufficient neutron detectors with different materials, structures and manufacturing processes, the key manufacturing and process parameters that affect the consistency factors of the self-sufficient neutron detector are found, and the tolerance range of each key parameter when the detector sensitivity consistency is met is given, so as to theoretically achieve the high sensitivity and consistency design of the self-sufficient neutron detector. (3) Regarding long life: On the one hand, Monte Carlo modeling and a hierarchical calculation method are used to accurately calculate the burnup life of the detector. On the other hand, by combining theory with experiment, the relationship between the mechanical properties of the detector component shell material and time in a typical pressurized water reactor operating environment is established, which enables accurate evaluation and prediction of the mechanical properties of the detector component shell at the end of the projectile burnup life.

[0063] The method of the present invention adopts a method combining self-balanced iterative calculation and global equilibrium iterative calculation to obtain the spatial charge, electric field and potential distribution in the SPND insulating layer in steady state. Specifically, (1) a calculation model of the spatial charge effect of the insulating layer of a self-powered neutron detector is established, and a "SPND insulating layer spatial charge effect calculation program" is constructed; (2) on the basis of step (1), a fine numerical simulation calculation of the SPND detector is carried out, and a "SPND fine numerical simulation calculation program" is constructed; (3) according to the sensitivity design requirements of SPND, two sets of calculation programs developed by the present invention are used to obtain the optimal detector structure size that meets the initial thermal neutron sensitivity requirements of SPND; (4) based on the optimal detector structure size determined in step (3), the influence of changes in the detector material parameters and geometric structure on the initial thermal neutron sensitivity of the detector is studied, and the factors affecting the initial thermal neutron sensitivity and consistency of the SPND detector are determined. (5) on the basis of step (4), the influence of the above key influencing factors on the initial thermal neutron sensitivity of the detector is studied, and within the range allowed by the SPND consistency, the maximum allowable tolerances of the key dimensions and key material parameters of the SPND detector are obtained through the above SPND Monte Carlo fine simulation program; (6) according to the SPND burnup stratification refinement algorithm and fA-level microcurrent signal processing technology, the SPND burnup life is further accurately obtained; (7) according to the relationship between the mechanical properties of the detector component shell material under the typical pressurized water reactor operating environment established by the present invention, the mechanical properties of the detector component shell at the end of the projectile burnup life are accurately judged, thereby obtaining the service life of the detector component shell.

[0064] The present invention provides systematic guidance for the design of self-powered neutron detectors. Through the present invention, the design of self-powered neutron detectors with high sensitivity, high consistency and long life can be achieved in theoretical design, which is of great significance for guiding the production and manufacturing and process control of detectors, detector (component) life assessment and component replacement plan design.

[0065] Example 1

[0066] like Figure 1 As shown, the design method of the self-powered neutron detector with high sensitivity and consistency of the present invention ensures the initial thermal neutron sensitivity and consistency of the detector from the source of theoretical design by systematically establishing the design criteria of the self-powered neutron detector, and provides a theoretical basis for the production and process control of the detector. Finally, the design of the self-powered neutron detector with high sensitivity and consistency and long life and the detector assembly is realized according to the operating function requirements of different nuclear reactors.

[0067] The method includes:

[0068] Step 1, by simulating the process of space charge in the insulating layer of the self-powered neutron detector from zero to steady state, a calculation model of space charge effect of the insulating layer of the self-powered neutron detector (SPND) is established to obtain the space charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector (SPND) in steady state;

[0069] When the electrons generated by the emitter of the self-powered neutron detector (SPND) pass through the insulating layer to the collector, they may be deposited due to insufficient energy, or the electrons in the insulating layer may be ionized and leave their original position, leaving a positive charge in place. Since the conductivity of the insulating layer is very poor, these charges cannot flow away or be neutralized in time and will accumulate in the insulating layer, thus forming a space charge distribution in the insulating layer, and then generating an electric field. The existence of the electric field will affect the electron transport process in the insulating layer, and then affect the generation of the detector output signal. This phenomenon is called the space charge effect of SPND. Therefore, in order to obtain accurate SPND thermal neutron sensitivity, the space charge effect must be taken into account in the Monte Carlo modeling calculation.

[0070] When the detector is just placed in a stable neutron-photon field, the amount of charge in the insulating layer is zero and the electric field strength is also zero. Then, as the amount of charge continues to accumulate, the electric field strength also increases, and the amount of charge lost due to the existence of the electric field gradually increases. Eventually, the amount of charge accumulated per unit time is equal to the amount of charge lost from the insulating layer, and the space charge and electric field reach a steady state. Therefore, if you want to calculate the space charge, potential, and electric field distribution in the SPND insulating layer, you need to simulate the process of the space charge in the insulating layer from nothing to something and then to a steady state.

[0071] In the calculation process of the present invention, by discretizing time, the stable net charge deposition rate distribution in the insulating layer at each discrete moment is calculated. When the net charge deposition rate at a certain moment is less than the set convergence limit, the charge distribution inside the insulating layer reaches a steady state, and then the distribution of the electric field and potential in the insulating layer is obtained. Among them, the net charge deposition rate corresponding to each discrete moment needs to be obtained by iterative calculation using the net charge deposition rate at the previous moment as the initial value, that is, a charge self-balancing iterative calculation needs to be performed in a single time step. After obtaining the stable net charge deposition rate distribution of the insulating layer at the current moment, the charge self-balancing calculation is performed in the next time step until a stable charge distribution is finally obtained. This process is a global equilibrium iterative calculation. In step 1 of the present invention, the spatial charge effect (spatial charge, potential, electric field distribution) in the insulating layer of the self-powered neutron detector in steady state is calculated, and the detailed calculation steps are as follows:

[0072] Step 11, using GEANT4 Monte Carlo software to establish a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector, using the neutron-photon source at the location of the self-powered neutron detector as the input of GEANT4, performing neutron-photon-electron coupled particle transport, and calculating the charge deposition rate distribution V in the insulating layer q (r,t);

[0073] Step 12, set the time step △t, take the charge deposition rate distribution and charge loss rate distribution at the previous moment in a single time step as the initial value at the current moment, and assume that the charge deposition rate and charge loss rate change linearly in a single time step, perform self-balancing calculation to obtain the stable charge distribution Q(r,t) at the current moment;

[0074] Q(r,t)=Q(r,t-Δt)+0.5·Δt[V q (r,t)+V q (r,t-Δt)]

[0075] Step 13: Divide the charge distribution Q(r, t) by the volume of the insulating layer to obtain the charge density distribution ρ(r, t); and further obtain the potential distribution of the insulating layer according to the Poisson equation

[0076]

[0077]

[0078] Where L is the SPND length, r1 is the inner radius of the insulation layer, r2 is the outer radius of the insulation layer, and ε is the dielectric constant of the insulation material.

[0079] Step 14: Based on the potential distribution of the insulating layer Further obtain the electric field distribution in the insulating layer and the current density distribution in the insulation layer

[0080]

[0081]

[0082] Where σ is the conductivity of the insulating material.

[0083] Step 15, according to the current density distribution and the surface area S(r) of the insulating layer, the new charge loss rate distribution V is calculated q,out (r,t);

[0084]

[0085] Step 16, when the charge loss rate distribution obtained from two consecutive calculations is less than the convergence residual of the self-balancing iterative calculation, the self-balancing iterative calculation converges; otherwise, repeat steps 11 to 15;

[0086] Step 17, if the net charge deposition rate calculated at the current moment is less than the convergence residual of the global equilibrium iterative calculation, the global equilibrium iterative calculation converges, and the spatial charge, potential, and electric field distribution in the insulating layer of the self-powered neutron detector in the steady state are obtained; otherwise, repeat steps 11 to 16.

[0087] Based on the above basic ideas, the present invention has developed a "SPND insulation layer space charge effect calculation program" corresponding to the self-powered neutron detector insulation layer space charge effect calculation model based on the GEANT4 Monte Carlo software. Through this program, the accurate calculation of the insulation layer space charge effect when the SPND size structure is arbitrarily set can be realized, and finally the calculation formula of the radial potential distribution in the SPND insulation layer is given.

[0088] Step 2, based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, taking into account the space charge effect of the insulating layer, a fine numerical simulation calculation of the self-powered neutron detector is performed;

[0089] Specifically, step 2 includes:

[0090] Step 21, based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, further construct a fine numerical simulation calculation model of the self-powered neutron detector;

[0091] Step 22, inputting the spatial charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in steady state into the fine numerical simulation calculation model of the self-powered neutron detector, accurately reconstructing the spatial electric field in the insulating layer of the self-powered neutron detector, and performing fine numerical simulation calculation of the self-powered neutron detector, further improving the accuracy of the simulation calculation of the self-powered neutron detector (SPND);

[0092] Among them, the "SPND fine numerical simulation calculation program" corresponding to the self-powered neutron detector fine numerical simulation calculation model is formed by adding the electromagnetic field interaction process to PhysicsList.cc of GEANT4.

[0093] In addition, a large number of information recording functions are added to SteepingAction.cc, EventAction.cc and RunAction.cc of GEANT4, which ultimately enables the "SPND fine numerical simulation calculation program" developed by the present invention to accurately calculate physical quantities such as average volume flux density, average surface flux density, average surface current density, charge deposition, energy deposition, particle energy spectrum, detector output total signal, component of detector output signal, electron escape probability, secondary particle energy spectrum generated by specified physical processes, reaction rate, decay current, initial thermal neutron sensitivity, etc.

[0094] Step 3, according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector, obtaining the optimal detector structure size that meets the initial thermal neutron sensitivity requirements of the self-powered neutron detector;

[0095] A SPND detector assembly usually arranges several SPNDs of the same size at equal intervals in its axial direction to measure the axial operating parameter distribution of the detector channel and ensure measurement accuracy when some SPND detectors fail.

[0096] Therefore, in practical engineering applications, firstly, according to the design requirements of the core measurement system, the number N of self-powered neutron detectors distributed axially in the self-powered neutron detector assembly, the length L of a single self-powered neutron detector and the maximum outer diameter R of a single self-powered neutron detector are obtained; then, the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and the fine numerical simulation calculation model of the self-powered neutron detector are used to optimize the structural dimensions of the self-powered neutron detector to ensure the highest initial thermal neutron sensitivity, and the optimal detector structural dimensions that meet the highest initial thermal neutron sensitivity requirements of the self-powered neutron detector are obtained.

[0097] A typical SPND is a three-coaxial cylindrical structure, which consists of an emitter, an insulator, and a collector from the inside to the outside. The specific structural optimization design steps and ideas are as follows:

[0098] (1) Collector: The function of the collector is to receive the electrons emitted from the emitter, thereby forming the detector output current signal. The collector is usually made of high temperature and radiation resistant materials such as Inconel. On the one hand, as the outer shell of a single SPND, the collector needs to have a certain mechanical strength, which requires that the tube wall of the collector cannot be too thin; on the other hand, if the tube wall of the collector is too thick, it will affect the neutron flux density entering the SPND. In actual engineering applications, the two sets of calculation programs developed by the present invention can be used to model the SPND, and the collector thickness can be changed during the calculation process to obtain the collector thickness for the optimal initial thermal neutron sensitivity.

[0099] (2) Insulation layer: The insulation layer is usually made of materials with good electrical insulation such as aluminum oxide and magnesium oxide. Its function is to separate the emitter and the collector. It is necessary to ensure that there is a certain degree of insulation between the emitter and the collector (usually the insulation resistance of SPND is required to be no less than 10 12 Ω), and at the same time, most of the electrons emitted by the emitter can be received by the collector to ensure that the detector has a sufficiently large neutron sensitivity. Assuming that the inner radius of the SPND insulation layer is r1, the outer radius is r2, the length is L, and the resistivity is ρ, the insulation resistance R between the inner and outer surfaces of the insulation layer is:

[0100]

[0101] According to the above-mentioned relationship between the insulation resistance and the inner and outer diameters of the insulation layer, two sets of calculation programs developed by the present invention are used to model the SPND. The thickness of the insulation layer is changed during the calculation process to obtain the relationship between the initial thermal neutron sensitivity of the SPND and the thickness of the insulation layer, thereby obtaining the thickness of the insulation layer when the optimal initial thermal neutron sensitivity is obtained.

[0102] (3) Emitter: After the emitter material captures neutrons, it emits gamma rays and beta rays. The interaction between gamma rays and detector materials will emit secondary electrons. These beta rays or secondary electrons form the detector output current signal after reaching the collector. After the size of the collector and the insulating layer is determined, the size of the emitter is also determined.

[0103] Step 4, based on the optimal detector structure size, analyze the influence of changes in detector material parameters and geometric structure on the initial thermal neutron sensitivity of the self-powered neutron detector, and determine the key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector;

[0104] Specifically, step 4 includes:

[0105] Step 41, based on the optimal detector structure size, analyze the factors affecting the detector material parameters and geometric structure on the initial thermal neutron sensitivity and consistency of the detector; the influencing factors include emitter impurity elements and content, emitter purity, emitter density, emitter length, emitter radius, emitter thickness uniformity, insulating layer impurity element composition and content, insulating layer purity, insulating layer density, insulating layer thickness, collector impurity elements and content, collector purity, collector density, collector thickness, etc.

[0106] Step 42, adopting a single control variable method and using a Monte Carlo simulation program to analyze the influence of changes in influencing factors on the initial thermal neutron sensitivity of the detector, and find out the key influencing factors that affect the initial thermal neutron sensitivity of the self-powered neutron detector.

[0107] Step 5, analyzing the influence of key influencing factors on the initial thermal neutron sensitivity of the detector, and using a Monte Carlo simulation program within the range allowed by the consistency of the self-powered neutron detector to obtain the maximum allowable tolerance of the key influencing factors;

[0108] On the basis of the key influencing factors of SPND initial thermal neutron sensitivity and consistency obtained in step 4, according to the consistency requirements of the core measurement system for the detector, the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and the fine numerical simulation calculation model of the self-powered neutron detector are used to study the influence of the changes of the above key factors on the thermal neutron sensitivity. Under the premise of meeting the requirements of SPND initial thermal neutron sensitivity, the maximum allowable tolerance of the above key dimensions or parameters is obtained to ensure the consistency of the detector from the design perspective.

[0109] Step 6, using the self-powered neutron detector burnup layering calculation method and fA-level micro-current signal processing technology to further accurately determine the burnup life of the self-powered neutron detector and improve the signal-to-noise ratio of the detector output signal;

[0110] Specifically, step 6 includes the following sub-steps:

[0111] Step 61, using a self-powered neutron detector burnup layering calculation method to obtain a relationship between the burnup of the emitter and time, and obtain the burnup life of the self-powered neutron detector;

[0112] Step 62, adopting fA-level micro-current signal processing technology to expand the measurement lower limit of the micro-current signal and improve the signal-to-noise ratio of the detector output signal.

[0113] Specifically, when the SPND detector is working in the core, its neutron sensitivity will gradually decrease with the consumption of sensitive materials. According to NB / T 20150 (2012), the SPND signal-to-noise ratio involved in the protection function should not be less than 10, and the SPND signal-to-noise ratio involved in the monitoring function should not be less than 2. The present invention adopts a layered calculation method for projectile burnup. By using the layered calculation method, the relationship between the change of projectile burnup and time can be accurately obtained, and the accurate SPND burnup life can be obtained. In addition, in the patent work of the present invention, a fA-level micro-current signal processing technology was developed, which expanded the measurement lower limit of the existing micro-current signal and further improved the signal-to-noise ratio.

[0114] Step 7, based on the established relationship between the change in mechanical properties of the self-powered neutron detector assembly shell material under a typical pressurized water reactor operating environment and time, determine the mechanical properties of the self-powered neutron detector assembly shell at the end of the projectile burnup life, and obtain the service life of the self-powered neutron detector assembly shell; wherein the self-powered neutron detector assembly arranges a plurality of self-powered neutron detectors of the same size in the axial direction.

[0115] Specifically, the shell of the SPND assembly serves as the pressure boundary of the reactor's primary circuit. At the end of the burnup life of the SPND assembly, it is necessary to ensure that it can be completely pulled out of the core. This requires evaluating the service life of the SPND assembly shell each time the core is replaced, and maximizing the life of the SPND assembly according to the burnup life calculated in step 6. The present invention establishes the relationship between the change of the mechanical properties of the SPND assembly shell material over time under a typical pressurized water reactor operating environment, which can be used to accurately determine the mechanical properties of the detector assembly shell at the end of the projectile burnup life, thereby determining whether the detector assembly can be successfully pulled out of the core at the end of the detector life.

[0116] The emitter materials of SPND are materials with high thermal neutron reaction cross sections such as rhodium, vanadium, cobalt, hafnium, and silver.

[0117] The insulating materials of SPND are inorganic insulating materials such as silicon dioxide, magnesium oxide, and aluminum oxide.

[0118] The collector material of SPND is nickel-based alloy Inconel600 with low neutron reaction cross section.

[0119] In the specific implementation, this embodiment takes the design of rhodium self-powered neutron detector and components as an example:

[0120] Step 1: Establish a computational model for the space charge effect in the insulating layer of the Rh-SPND

[0121] In the process of passing through the insulating layer to the collector, the electrons generated by the Rh-SPND emitter may be deposited due to insufficient energy, or the electrons in the insulating layer may be ionized and leave their original position, leaving a positive charge in place. Since the conductivity of the insulating layer is very poor, these charges cannot flow away or be neutralized in time and will accumulate in the insulating layer, thereby forming a spatial charge distribution in the insulating layer, and then generating an electric field. The existence of the electric field will affect the electron transport process in the insulating layer, and then affect the generation of the detector output signal. This phenomenon is called the spatial charge effect of Rh-SPND. Therefore, in order to obtain accurate Rh-SPND thermal neutron sensitivity, the spatial charge effect must be taken into account in the Monte Carlo modeling calculation.

[0122] When the detector is just placed in a stable neutron-photon field, the amount of charge in the insulating layer is zero and the electric field strength is also zero. Then, as the amount of charge continues to accumulate, the electric field strength also increases, and the amount of charge lost due to the existence of the electric field gradually increases. Eventually, the amount of charge accumulated per unit time is equal to the amount of charge lost from the insulating layer, and the space charge and electric field reach a steady state. Therefore, if you want to calculate the space charge, potential, and electric field distribution in the Rh-SPND insulating layer, you need to simulate the process of the space charge in the insulating layer from nothing to something and then to a steady state.

[0123] The present invention adopts the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector (SPND), and can calculate the following: Figure 2 The relationship between the charge change rate (net deposition rate, deposition rate and loss rate) in the Rh-SPND insulating layer and time, and Figure 3 , Figure 4 and Figure 5 The charge density, potential distribution and electric field distribution in the Rh-SPND insulating layer at different times are shown in FIG. Figure 4 The potential distribution curve along the radial direction in the SPND insulating layer and the electron kinetic energy threshold in the insulating layer can be further obtained.

[0124] Step 2: Detailed numerical simulation of SPND detector considering the space charge effect of the insulating layer

[0125] On the basis of using GEANT4 Monte Carlo software to establish the Rh-SPND calculation model in step 1, the present invention further develops a "SPND fine numerical simulation calculation program" corresponding to the fine numerical simulation calculation model of the self-powered neutron detector. The program uses the space charge, potential, and electric field distribution of the insulating layer obtained in step 1 as input, accurately reconstructs the space electric field in the SPND insulating layer, and further improves the accuracy of the SPND simulation calculation. In addition, a large number of information recording functions are added to the calculation program, which ultimately enables the SPND fine numerical simulation calculation program developed by the present invention to accurately calculate the average volume flux density, average surface flux density, average surface current density, charge deposition, energy deposition, particle energy spectrum, detector output total signal, detector output signal composition, electron escape probability, secondary particle energy spectrum generated by a specified physical process, reaction rate, decay current, initial thermal neutron sensitivity and other physical quantities.

[0126] Table 1 shows the variation of electron escape probability with emitter radius, Table 2 shows the variation of electron escape probability with insulating layer thickness, and Table 3 gives detailed information on the initial thermal neutron sensitivity of Rh-SPND. The results show that the electron escape probability varies greatly with the increase of emitter radius and insulating layer thickness, and emitter radius and insulating layer thickness are important factors affecting electron escape probability and initial thermal neutron sensitivity.

[0127] Table 1 Variation of electron escape probability with emitter radius (unit: %)

[0128]

[0129] Table 2 Variation of electron escape probability with insulating layer thickness (unit: %)

[0130]

[0131]

[0132] Table 3 Details of the initial thermal neutron sensitivity of Rh-SPND

[0133]

[0134] Step 3: Under the premise of meeting the engineering design requirements, achieve high sensitivity design through SPND structural optimization design

[0135] A SPND detector assembly usually has several SPNDs of the same size arranged at equal intervals in the axial direction to measure the distribution of the axial operating parameters of the detector channel and ensure the measurement accuracy when some SPND detectors fail. Therefore, in actual engineering applications, firstly, according to the design requirements of the core measurement system, the number N of SPNDs distributed axially in the detector assembly, the length L of a single SPND, and the maximum outer diameter R of a single SPND are obtained; then, based on steps 2 and 3, the structural dimensions of the SPND are optimized and designed using the "SPND insulation layer space charge effect calculation program" and "SPND fine numerical simulation calculation program" of the present invention to ensure the highest initial thermal neutron sensitivity.

[0136] For the collector, the mechanical strength of a single Rh-SPND and the influence of the collector thickness on the initial thermal neutron sensitivity of the Rh-SPND are comprehensively considered, and by using the calculation program of the present invention to perform Rh-SPND modeling calculations, it is found that in actual engineering applications, the optimal thickness of the Rh-SPND collector is about 0.25 mm.

[0137] For the insulation layer, assuming that the inner radius of the SPND insulation layer is r1, the outer radius is r2, the length is L, and the resistivity is ρ, the insulation resistance R between the inner and outer surfaces of the insulation layer is:

[0138]

[0139] The insulation resistance requirement for SPND is usually not less than 10 12 Ω, taking the silicon dioxide insulating layer as an example, its resistivity is 1×10 13 Ω·m, considering a certain design margin, the relationship between the inner and outer diameters and the length of the Rh-SPND insulation layer is ln(r2 / r1)≥1.256l. On this basis, the Rh-SPND modeling calculation is performed using the calculation program of the present invention, and it is found that in actual engineering applications, the optimal thickness of the Rh-SPND insulation layer is about 0.12mm to 0.20mm.

[0140] The results of modeling calculations show that: Figure 6As shown in , when the detector length is constant and the emitter radius is constant, the thicker the insulating layer, the smaller the initial thermal neutron sensitivity of the detector; Figure 7 and Figure 8 As shown, when the thickness of the insulating layer remains unchanged, the initial thermal neutron sensitivity of the detector increases with the increase of the emitter length and the increase of the emitter radius.

[0141] Step 4: Based on step 3, analyze the key factors affecting the sensitivity and consistency of the self-powered neutron detector

[0142] On the basis of determining the optimal structure size of SPND in step 3, the influence of SPND material properties and geometric structure on the initial thermal neutron sensitivity and consistency of the detector is studied. The influencing factors studied include emitter impurity elements and content, emitter purity, emitter density, emitter length, emitter radius, emitter thickness uniformity, insulating layer impurity element composition and content, insulating layer purity, insulating layer density, insulating layer thickness, collector impurity elements and content, collector purity, collector density, collector thickness, etc. The single control variable method is adopted, and the above "SPND insulating layer space charge effect calculation program" and "SPND fine numerical simulation calculation program" of the present invention are used to study the influence of the above factors on the initial thermal neutron sensitivity of the detector when they change. The results show that the emitter length, emitter radius and insulating layer thickness are the key factors affecting the sensitivity and consistency of the self-powered neutron detector.

[0143] Step 5: According to the engineering design requirements, determine the key dimension tolerance or parameter tolerance of the detector that meets the SPND initial thermal neutron sensitivity consistency requirements.

[0144] On the basis of the SPND initial thermal neutron sensitivity and key influencing factors of consistency obtained in step 4, according to the consistency requirements of the core measurement system for the detector, the "SPND insulating layer space charge effect calculation program" and "SPND fine numerical simulation calculation program" of the present invention are used to study the influence of changes in emitter length, emitter radius and insulating layer thickness on thermal neutron sensitivity. On the premise of meeting the SPND initial thermal neutron sensitivity requirements, the maximum allowable tolerances of the three key dimensions of emitter length, emitter radius and insulating layer thickness are obtained to ensure the consistency of the detector from a design perspective.

[0145] Step 6: Use a hierarchical calculation method to accurately calculate the burnup life of SPND

[0146] When the SPND detector is working in the core, its neutron sensitivity will gradually decrease with the consumption of sensitive materials. The present invention adopts a projectile burnup layering calculation method. Fig. 9The burnup life analysis results of the self-powered neutron detector emitter are compared with the burnup life analysis method of the self-powered neutron detector described in the present invention. The calculation accuracy of the burnup life is greatly improved through the layered and refined calculation of the present invention.

[0147] Step 7: SPND Component Housing Service Life Assessment and Prediction

[0148] The shell of the SPND assembly serves as the pressure boundary of the reactor's primary circuit. At the end of the burnup life of the SPND assembly, it is necessary to ensure that it can be completely pulled out of the core. This requires evaluating the service life of the SPND assembly shell each time the core is replaced, and maximizing the life of the SPND assembly based on the burnup life calculated in the sixth step. The present invention establishes the relationship between the change of the mechanical properties of the detector assembly shell material over time under a typical pressurized water reactor operating environment, which can be used to accurately determine the mechanical properties of the detector assembly shell at the end of the projectile burnup life, thereby determining whether the detector assembly can be successfully pulled out of the core at the end of the detector life. Fig.10 The accelerated aging analysis method for the material performance of the shell of the self-powered neutron detector assembly of the present invention is the nanohardness of 316L stainless steel after irradiation, based on which the mechanical properties of the detector assembly shell at the end of the projectile burnup life can be accurately inferred.

[0149] The new method proposed in the present invention ensures the high sensitivity and consistency of the SPND detector from the design level, and ensures the long life of the SPND detector and the detector assembly, which is of great significance for the manufacture of the SPND detector and the assembly. The present invention can provide systematic guidance for the design of self-powered neutron detectors, realize the design of self-powered neutron detectors with high sensitivity and high consistency and long life in theoretical design, and guide the production and manufacturing of detectors and process control, detector (assembly) life assessment and assembly replacement scheme design.

[0150] Example 2

[0151] like Fig.11 As shown, the difference between this embodiment and embodiment 1 is that this embodiment provides a self-powered neutron detector design system with high sensitivity and consistency, and the system uses the self-powered neutron detector design method with high sensitivity and consistency of embodiment 1; the system includes:

[0152] A calculation model building unit is used to build a calculation model of the space charge effect of the insulation layer of the self-powered neutron detector by simulating the process of the space charge in the insulation layer of the self-powered neutron detector from nothing to something and then to a steady state, so as to obtain the space charge, potential and electric field distribution in the insulation layer of the self-powered neutron detector in a steady state;

[0153] A fine calculation model building unit is used to perform fine numerical simulation calculations of the self-powered neutron detector based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and taking into account the space charge effect of the insulating layer;

[0154] An optimal structural dimension obtaining unit is used to obtain an optimal detector structural dimension that meets the initial thermal neutron sensitivity requirement of the self-powered neutron detector according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector;

[0155] A key influencing factor determination unit is used to analyze the influence of changes in detector material parameters and geometric structure on the initial thermal neutron sensitivity of the self-powered neutron detector based on the optimal detector structure size, and determine the key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector;

[0156] The maximum allowable tolerance analysis unit is used to analyze the impact of key influencing factors on the initial thermal neutron sensitivity of the detector. Within the range allowed by the consistency of the self-powered neutron detector, the maximum allowable tolerance of the key influencing factors is obtained by using the Monte Carlo simulation program;

[0157] The burnup life determination unit is used to further accurately determine the burnup life of the self-powered neutron detector by using the burnup layering calculation method of the self-powered neutron detector and the fA-level micro-current signal processing technology, and improve the signal-to-noise ratio of the detector output signal;

[0158] The service life determination unit is used to determine the mechanical properties of the shell of the self-powered neutron detector assembly at the end of the projectile burnup life according to the established relationship between the mechanical properties of the shell material of the self-powered neutron detector assembly and time in a typical pressurized water reactor operating environment, so as to obtain the service life of the shell of the self-powered neutron detector assembly; wherein the self-powered neutron detector assembly arranges a plurality of self-powered neutron detectors of the same size in the axial direction.

[0159] Among them, the execution process of each unit can be executed according to the process steps of the high-sensitivity and consistent self-powered neutron detector design method in Example 1, and will not be repeated one by one in this embodiment.

[0160] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0161] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0162] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0163] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0164] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing a self-powered neutron detector with high sensitivity and consistency, characterized in that: The method includes: Step 1, establishing a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector, and obtaining the space charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in a steady state; Step 2, based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, taking into account the space charge effect of the insulating layer, a fine numerical simulation calculation of the self-powered neutron detector is performed; Step 3, according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector, obtaining the optimal detector structure size that meets the initial thermal neutron sensitivity requirements of the self-powered neutron detector; Step 4, determining key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector according to the optimal detector structure size; Step 5, analyzing the influence of the key influencing factors on the initial thermal neutron sensitivity of the detector, and using a Monte Carlo simulation program within the range allowed by the consistency of the self-powered neutron detector to obtain the maximum allowable tolerance of the key influencing factors; Step 6, using the self-powered neutron detector burnup layering calculation method and fA-level micro-current signal processing technology to further determine the burnup life of the self-powered neutron detector and improve the signal-to-noise ratio of the detector output signal; Step 1 includes the following sub-steps: Step 11, using Monte Carlo software to establish a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector, using the neutron-photon source at the location of the self-powered neutron detector as the input of GEANT4, performing neutron-photon-electron coupled particle transport, and calculating the charge deposition rate distribution in the insulating layer; Step 12, setting the time step, taking the charge deposition rate distribution and charge loss rate distribution at the previous moment in a single time step as the initial value at the current moment, and assuming that the charge deposition rate and the charge loss rate change linearly within a single time step, performing self-balancing calculation to obtain a stable charge distribution at the current moment; Step 13, dividing the charge distribution by the volume of the insulating layer to obtain a charge density distribution; and further obtaining an insulating layer potential distribution according to the Poisson equation; Step 14, further obtaining the electric field distribution in the insulating layer and the current density distribution in the insulating layer according to the electric potential distribution of the insulating layer; Step 15, calculating a new charge loss rate distribution according to the current density distribution and the outer surface area of ​​the insulating layer; Step 16, when the charge loss rate distribution obtained from two consecutive calculations is less than the convergence residual of the self-balancing iterative calculation, the self-balancing iterative calculation converges; otherwise, repeat steps 11 to 15; Step 17, if the net charge deposition rate calculated at the current moment is less than the convergence residual of the global equilibrium iterative calculation, the global equilibrium iterative calculation converges, and the spatial charge, potential, and electric field distribution in the insulating layer of the self-powered neutron detector in the steady state are obtained; otherwise, repeat steps 11 to 16.

2. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 1, characterized in that: The method further includes: Based on the established relationship between the mechanical properties of the shell material of the self-powered neutron detector assembly and time in a typical pressurized water reactor operating environment, the mechanical properties of the shell of the self-powered neutron detector assembly at the end of the projectile burnup life are determined, and the service life of the shell of the self-powered neutron detector assembly is obtained; Wherein, the self-powered neutron detector assembly arranges a plurality of self-powered neutron detectors of the same size in the axial direction.

3. The method for designing a highly sensitive and consistent self-powered neutron detector according to claim 1, characterized in that: Step 2 includes: Based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, a fine numerical simulation calculation model of the self-powered neutron detector is further constructed; Inputting the spatial charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in steady state into the self-powered neutron detector fine numerical simulation calculation model, reconstructing the spatial electric field in the insulating layer of the self-powered neutron detector, and performing the self-powered neutron detector fine numerical simulation calculation; The self-powered neutron detector fine numerical simulation calculation model is formed by adding the electromagnetic field interaction process to PhysicsList.cc of GEANT4.

4. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 1, characterized in that: Step 3 includes: According to the design requirements of the core measurement system, the number of self-powered neutron detectors distributed axially in the self-powered neutron detector assembly, the length of a single self-powered neutron detector and the maximum outer diameter of a single self-powered neutron detector are obtained; The calculation model of space charge effect of the insulating layer of the self-powered neutron detector and the fine numerical simulation calculation model of the self-powered neutron detector are used to optimize the structural dimensions of the self-powered neutron detector and obtain the optimal detector structural dimensions that meet the highest initial thermal neutron sensitivity requirements.

5. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 4, characterized in that: The optimal detector structure dimensions include the collector thickness at the optimal initial thermal neutron sensitivity, the insulating layer thickness at the optimal initial thermal neutron sensitivity, and the emitter size at the optimal initial thermal neutron sensitivity.

6. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 1, characterized in that: Step 4 includes: According to the optimal detector structure size, analyzing the factors affecting the detector material parameters and geometric structure on the initial thermal neutron sensitivity and consistency of the detector; The single control variable method is used to analyze the influence of the influencing factors on the initial thermal neutron sensitivity of the detector by using the Monte Carlo simulation program, and the key influencing factors affecting the initial thermal neutron sensitivity of the self-powered neutron detector are determined.

7. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 6, characterized in that: The influencing factors include emitter impurity elements and content, emitter purity, emitter density, emitter length, emitter radius, emitter thickness uniformity, insulating layer impurity element composition and content, insulating layer purity, insulating layer density, insulating layer thickness, collector impurity elements and content, collector purity, collector density, and collector thickness.

8. The method for designing a self-powered neutron detector with high sensitivity and consistency according to claim 1, characterized in that: Step 6 includes the following sub-steps: The burnup layering calculation method of the self-powered neutron detector is used to obtain the relationship between the burnup of the emitter and time, and the burnup life of the self-powered neutron detector is obtained. Adopting fA-level micro-current signal processing technology, the measurement lower limit of micro-current signals is expanded and the signal-to-noise ratio of the detector output signal is improved.

9. A self-powered neutron detector design system with high sensitivity and consistency, characterized by: The system includes: A calculation model building unit is used to build a calculation model of the space charge effect of the insulating layer of the self-powered neutron detector, and obtain the space charge, potential and electric field distribution in the insulating layer of the self-powered neutron detector in a steady state; A fine calculation model building unit is used to perform fine numerical simulation calculations of the self-powered neutron detector based on the calculation model of the space charge effect of the insulating layer of the self-powered neutron detector and taking into account the space charge effect of the insulating layer; An optimal structural dimension obtaining unit is used to obtain an optimal detector structural dimension that meets the initial thermal neutron sensitivity requirement of the self-powered neutron detector according to the design requirements of the core measurement system and the sensitivity design requirements of the self-powered neutron detector; A key influencing factor determination unit, used to determine the key influencing factors affecting the initial thermal neutron sensitivity and consistency of the self-powered neutron detector according to the optimal detector structure size; A maximum allowable tolerance analysis unit is used to analyze the influence of the key influencing factors on the initial thermal neutron sensitivity of the detector, and to obtain the maximum allowable tolerance of the key influencing factors by using a Monte Carlo simulation program within the range allowed by the consistency of the self-powered neutron detector; The burnup life determination unit is used to further determine the burnup life of the self-powered neutron detector by using the burnup layering calculation method of the self-powered neutron detector and the fA-level micro-current signal processing technology, so as to improve the signal-to-noise ratio of the detector output signal; A service life determination unit is used to determine the mechanical properties of the shell of the self-powered neutron detector assembly at the end of the projectile burnup life according to the established relationship between the mechanical properties of the shell material of the self-powered neutron detector assembly and time in a typical pressurized water reactor operating environment, so as to obtain the service life of the shell of the self-powered neutron detector assembly; The execution process of the calculation model building unit is: Step 11, using Monte Carlo software to establish a calculation model for the space charge effect of the insulating layer of the self-powered neutron detector, using the neutron-photon source at the location of the self-powered neutron detector as the input of GEANT4, performing neutron-photon-electron coupled particle transport, and calculating the charge deposition rate distribution in the insulating layer; Step 12, setting the time step, taking the charge deposition rate distribution and charge loss rate distribution at the previous moment in a single time step as the initial value at the current moment, and assuming that the charge deposition rate and the charge loss rate change linearly within a single time step, performing self-balancing calculation to obtain a stable charge distribution at the current moment; Step 13, dividing the charge distribution by the volume of the insulating layer to obtain a charge density distribution; and further obtaining an insulating layer potential distribution according to the Poisson equation; Step 14, further obtaining the electric field distribution in the insulating layer and the current density distribution in the insulating layer according to the electric potential distribution of the insulating layer; Step 15, calculating a new charge loss rate distribution according to the current density distribution and the outer surface area of ​​the insulating layer; Step 16, when the charge loss rate distribution obtained from two consecutive calculations is less than the convergence residual of the self-balancing iterative calculation, the self-balancing iterative calculation converges; otherwise, repeat steps 11 to 15; Step 17, if the net charge deposition rate calculated at the current moment is less than the convergence residual of the global equilibrium iterative calculation, the global equilibrium iterative calculation converges, and the spatial charge, potential, and electric field distribution in the insulating layer of the self-powered neutron detector in the steady state are obtained; otherwise, repeat steps 11 to 16.

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