Monocrystalline silicon neutron irradiation monitoring method and system based on vanadium self-powered detector

Abstract

The invention discloses a monocrystalline silicon neutron irradiation monitoring method and system based on a vanadium self-powered detector, and belongs to the field of nuclear engineering. The monocrystalline silicon neutron irradiation monitoring method based on the vanadium self-powered detector comprises the following steps: calculating a corresponding relation between the burnup depth and nuclide components of a fuel assembly and a corresponding relation between axial burnup distribution of the fuel assembly and fuel circulation and the burnup depth; calculating to obtain a corresponding relationship between the thermal neutron fluence rate of the irradiation pore channel and the burnup cycle and the burnup depth; and taking a position where the thermal neutron fluence rate of the irradiation pore channel does not exceed a given threshold value as a detector mounting area, and calibrating a corresponding relation between a vanadium self-powered detector signal mounted in the detector mounting area and the thermal neutron fluence rate of the irradiation pore channel by using an activated foil, thereby monitoring the thermal neutron fluence rate of the monocrystalline silicon by using the vanadium self-powered detector.

Description

Technical Field

[0001] The invention belongs to the field of nuclear engineering, and in particular relates to a single crystal silicon neutron irradiation monitoring method and system based on a vanadium self-powered detector. Background Art

[0002] Neutron irradiation transmutation doping (NTD) treatment of single crystal silicon can provide semiconductor materials with good comprehensive performance, and has good application prospects in the fields of semiconductor manufacturing, nuclear physics experiments, etc. In order to ensure that the resistivity of single crystal silicon after neutron irradiation accurately reaches the target value, it is necessary to accurately control the cumulative thermal neutron fluence of single crystal silicon neutron irradiation. At present, activated foil is usually used to measure the cumulative thermal neutron fluence of single crystal silicon neutron irradiation, but the activated foil measurement method belongs to offline measurement and cannot monitor the thermal neutron fluence rate online. Although rhodium self-powered detectors can be used for online monitoring of thermal neutron fluence, rhodium has a high burnup rate and a short service life, which cannot meet the needs of long-term use, and the self-powered detectors in the irradiation channel are difficult to frequently repair or replace. Vanadium has a low burnup rate and can have a longer service life as a self-powered detector material, but the current signal output by the self-powered detector made of vanadium cannot directly reflect the thermal neutron fluence rate, and there is a problem of detection accuracy.

[0003] Patent CN103314309A discloses a rhodium-vanadium dual-emitter detector, which uses a rhodium detector to calibrate a vanadium detector and uses the vanadium detector to continue working after the rhodium detector fails. However, this technical solution is used to detect the power distribution of the reactor core, which is very different from the working environment of the irradiation channel of the research reactor. It cannot be applied to the online detection of thermal neutron injection during the treatment of single crystal silicon NTD. At the same time, the detection accuracy after the rhodium detector fails lacks effective guarantee.

[0004] Therefore, providing a single crystal silicon neutron irradiation monitoring method has positive significance for improving the quality of single crystal silicon NTD products. Summary of the invention

[0005] The purpose of the present invention is to provide a single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector, which can accurately monitor the thermal neutron injection rate of single crystal silicon subjected to neutron irradiation for a long time in real time. The present invention also provides a single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector.

[0006] According to an embodiment of one aspect of the present invention, a method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector is provided, the method comprising the following steps:

[0007] Step a): establishing a fuel assembly burnup model for a research reactor used for single crystal silicon neutron irradiation treatment, and calculating the corresponding relationship between the burnup depth and the nuclide composition of the fuel assembly;

[0008] Step b): establishing a core model of the research reactor, and calculating the corresponding relationship between the axial burnup distribution of the fuel assembly and the fuel cycle and burnup depth according to the calculation result of step a);

[0009] Step c): establishing an irradiation channel model of the research reactor, coupling the irradiation channel model with the core model and the heavy water reflector, and calculating the corresponding relationship between the irradiation channel thermal neutron injection rate and the burnup cycle and burnup depth;

[0010] Step d): Calculate the area whose difference from the thermal neutron fluence rate in the irradiation channel does not exceed a given threshold as the detector installation area;

[0011] Step e): providing a vanadium self-powered detector, installing the vanadium self-powered detector in the detector installation area, installing an activated foil in the irradiation channel, adjusting the rod position of the control rod of the research reactor, using the activated foil to measure the corresponding relationship between the rod position of the control rod and the thermal neutron flux rate in the irradiation channel, and then obtaining the output signal intensity of the vanadium self-powered detector and the calibration coefficient of the thermal neutron flux rate in the irradiation channel, and completing the calibration of the vanadium self-powered detector;

[0012] Step f): performing irradiation treatment on the single crystal silicon, and using the vanadium self-powered detector to monitor the thermal neutron injection rate of the single crystal silicon.

[0013] This method uses vanadium self-powered detectors with rich engineering application experience in large-scale advanced passive pressurized water reactors, effectively overcomes the shortcomings of rhodium self-powered neutron detectors such as low burnup rate and long burnup life, and can realize online monitoring of single crystal silicon irradiation neutron injection.

[0014] Furthermore, in some embodiments, in the step b), the core model is calculated using an adaptive grid in the axial direction.

[0015] Furthermore, in step c) in some embodiments, a Monte Carlo program is used for modeling and calculation.

[0016] The full-core Monte Carlo high-precision modeling and analysis technology can accurately obtain the thermal neutron injection rate of the irradiation channel position in the heavy water reflector area at different fuel cycles and different burnup depths. The vanadium self-powered detector is arranged in the neutron detector channel around the single crystal silicon irradiation channel. The neutron detector is isolated from the strong radiation medium of the research reactor through the channel, which effectively overcomes technical difficulties such as maintenance and replacement. In the single crystal silicon neutron irradiation test phase, the relationship between the vanadium self-powered detector calibration factor and the core state is obtained. In the single crystal silicon neutron irradiation production phase, the calibration factor is used to obtain the single crystal silicon irradiation neutron injection, which effectively improves the hit rate of the single crystal silicon neutron irradiation target resistivity.

[0017] Furthermore, in some embodiments, in step c), based on the calculation results of step a) and step b), the axial nuclide nucleon density distribution of the fuel assembly is obtained by Lagrange interpolation method as material information input into the Monte Carlo program.

[0018] Furthermore, in some embodiments, in the step d), the given threshold does not exceed 10%.

[0019] Furthermore, in some embodiments, in the step d), calculation is performed within a given radius around the irradiation channel to determine the detector installation area.

[0020] Furthermore, in some embodiments, in the step e), at least two vanadium self-powered detectors are installed around each irradiation channel.

[0021] Furthermore, in some embodiments, in the step e), at least one vanadium self-powered detector is installed on both sides of a line connecting the center of the irradiation channel and the center of the research reactor core.

[0022] Furthermore, in some embodiments, in the step e), the scale coefficient is calculated by least squares fitting.

[0023] According to another embodiment of the present invention, a single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector is provided, which is used in the single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector provided in any of the above embodiments, and includes a vanadium self-powered detector, a signal transmission cable and a signal processor. The vanadium self-powered detector monitors the thermal neutron flux rate in the detector installation area and transmits the electrical signal to the signal processor through the signal transmission cable, and the signal processor calculates and outputs the corresponding thermal neutron flux rate in the irradiation channel according to the scale factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of a single crystal silicon neutron irradiation device for a research reactor in one embodiment;

[0025] Figure 2 Schematic diagram of the structure of a single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector in one embodiment.

[0026] Meaning of the reference symbols:

[0027] 1- research reactor core; 2- single crystal silicon irradiation channel; 3- self-powered detector installation position; 4- heavy water reflector; 5- single crystal silicon; 6- vanadium self-powered detector; 7- signal transmission cable; 8- signal processor; 9- human-machine terminal.

[0028] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. For the sake of simplicity, the above drawings only schematically illustrate the structures related to the technical features of the present invention, and do not strictly draw the complete device and all details according to the actual proportion. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0030] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0031] In the description of this article, unless otherwise clearly specified and limited, the technical terms "installed", "connected", "connected" and the like should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection; it can be a movable connection or a fixed connection or an integrated connection. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

[0032] In the description of this document, terms indicating orientation or positional relationships, such as "up", "down", "left", "right", "horizontal", "vertical", "height", "length", and "width", are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be construed as a limitation on the embodiments in this document.

[0033] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0034] Single crystal silicon neutron irradiation production is one of the important applications of research reactors. During the single crystal silicon neutron irradiation process, in order to ensure that the resistivity of the single crystal silicon after neutron irradiation accurately reaches the target value and improve the hit rate of the target resistivity of the single crystal silicon neutron irradiation, the cumulative thermal neutron injection of the single crystal silicon neutron irradiation must be accurately controlled. The traditional method uses the activated foil method to measure the cumulative thermal neutron injection of single crystal silicon neutron irradiation, which is an offline measurement method and cannot monitor the changes of the neutron injection of the single crystal silicon irradiation over time online. Some schemes have proposed a method of using rhodium self-powered neutron detectors to monitor the thermal neutron injection of single crystal silicon irradiation online, which can monitor the changes of the thermal neutron injection of single crystal silicon irradiation over time in real time. However, the rhodium self-powered neutron detector has a high burnup rate and a short burnup life. Usually, its service life is only a few years, which cannot meet the needs of long-term online measurement of the neutron injection of single crystal silicon irradiation. In addition, the rhodium self-powered neutron detector is arranged on the outer wall of the single crystal silicon irradiation channel. It is difficult to inspect and replace the rhodium self-powered neutron detector under the strong radiation environment of the research reactor.

[0035] In order to solve the above problems, an embodiment of one aspect of the present invention provides a method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector, which uses a vanadium self-powered detector to monitor the thermal neutron flux of single crystal silicon irradiation online. The vanadium self-powered detector has the characteristics of high measurement accuracy, low burnup rate, and long burnup life. The service life is up to ten or even several decades, which can meet the needs of long-term online monitoring of the thermal neutron flux of single crystal silicon irradiation. At the same time, by arranging the vanadium self-powered detector in the neutron detector channel around the single crystal silicon irradiation channel, the position of the neutron detector channel is determined by neutron calculation program analysis, so that the thermal neutron flux at the neutron detector channel position and the thermal neutron flux at the single crystal silicon irradiation channel position are within ±10%. The neutron detector is isolated from the strong radiation medium of the research reactor through the channel, which effectively overcomes technical difficulties such as maintenance and replacement.

[0036] When the vanadium self-powered detector is arranged in the neutron detector channel around the single crystal silicon irradiation channel, the current signal output by the vanadium self-powered detector cannot directly reflect the thermal neutron injection rate at the position of the single crystal silicon. It is necessary to calibrate the vanadium self-powered detector and determine the scale factor. The scale factor is defined as the ratio of the current signal of the vanadium self-powered detector to the thermal neutron injection rate of the single crystal silicon. In addition, when the core state of the research reactor changes and causes the neutron energy spectrum to change, due to the difference in the position of the vanadium self-powered detector and the single crystal silicon, the changes in the thermal neutron energy spectrum received by the two are different, so the scale factor needs to be corrected. Based on the corrected scale factor, combined with the current signal of the vanadium self-powered detector, the thermal neutron injection rate of the single crystal silicon irradiation can be monitored online, effectively improving the hit rate of the single crystal silicon neutron irradiation target resistivity.

[0037] In one embodiment, the method comprises the following steps:

[0038] Step a): Establish a database of nuclide composition of fuel assemblies at different burnup depths.

[0039] The Monte Carlo program based on probability theory is used to calculate the nuclide distribution at each burnup depth for each type of fuel assembly in the research reactor, and the corresponding relationship between the burnup depth and the nuclide composition of the fuel assembly is obtained to form a fuel assembly nuclide composition database.

[0040] Step b): Carry out multi-fuel cycle calculations for the research reactor core.

[0041] The whole core of the research reactor was modeled using a nuclear design program based on the deterministic method. The control rod positions at different burnup depths were considered, and the adaptive grid technology was used axially to complete the multi-fuel cycle calculations of the research reactor. The axial burnup distribution of each box of fuel assembly in the whole core at different fuel cycles and different burnup depths was obtained, and the corresponding relationship between the axial burnup distribution of the fuel assembly and the fuel cycle and burnup depth was obtained.

[0042] Step c): Establish a high-precision Monte Carlo model of the research reactor core and perform high-precision Monte Carlo calculations.

[0043] Using the fuel assembly nuclide composition database obtained in step a) and the axial burnup distribution of the fuel assembly obtained in step b), the Lagrange interpolation method is used to obtain the axial nuclide nucleon density distribution of each box of fuel assemblies, and the material information required for the full-core Monte Carlo modeling is generated. At the same time, the Monte Carlo program is used to perform high-precision modeling of the irradiation channel, and the full-core Monte Carlo high-precision modeling of the coupled research reactor core area and the heavy water reflector area is achieved, such as Figure 1 As shown, it includes a research reactor core 1, a single crystal silicon irradiation channel 2, and a heavy water reflector 4. A full-core Monte Carlo calculation is carried out to couple the research reactor core region and the heavy water reflector region to accurately obtain the thermal neutron injection rate of the irradiation channel position in the heavy water reflector region under different fuel cycles and different burnup depths. Thus, the corresponding relationship between the thermal neutron injection rate of the single crystal silicon irradiation channel 2 and the burnup cycle and burnup depth is obtained.

[0044] Step d): Determine the installation location of the vanadium self-powered detector.

[0045] The thermal neutron flux rate near the single crystal silicon irradiation channel 2 (within a given radius) is calculated, and an area where the difference between the thermal neutron flux rate in the single crystal silicon irradiation channel 2 and the thermal neutron flux rate in the fuel cycle period does not exceed a given threshold is found as the detector installation area. In a preferred embodiment, the given threshold does not exceed 10%.

[0046] During the neutron irradiation of single crystal silicon, the single crystal silicon will rotate at a uniform speed around the axis along with the storage tank (device for loading single crystal silicon). Considering the accuracy of thermal neutron injection measurement, at least one position is selected on both sides of the connecting line a between the center of the research reactor core 1 and the center of the single crystal silicon irradiation channel 2 (in the range of 0° to 180° and 180° to 360°) as the self-powered detector installation position 3.

[0047] Step e): Calibration of the vanadium self-powered detector.

[0048] When the core state of the research reactor changes, causing the neutron energy spectrum to change, due to the difference in the position of the vanadium self-powered detector and the single crystal silicon, the changes in the thermal neutron energy spectrum received by the two are different, so it is necessary to introduce a calibration coefficient for correction. The main factors affecting the neutron energy spectrum of the vanadium self-powered detector and the single crystal silicon position include: control rod position, changes in core loading, fuel element burnup, vanadium self-powered detector emitter self-burnup, etc. After analysis, the present invention found that the calibration coefficient is mainly affected by the control rod position. This technical solution determines the fitting relationship between the vanadium self-powered detector calibration factor and the core control rod position in the single crystal silicon neutron irradiation test stage, and applies the fitting relationship in the single crystal silicon neutron irradiation production stage to obtain the vanadium self-powered detector calibration factor corresponding to different control rod positions. The specific steps are as follows:

[0049] During the single crystal silicon neutron irradiation test phase, the vanadium self-powered detector was transferred to the self-powered detector installation position 3, and the activated foil was installed in the single crystal silicon irradiation channel 2. The activated foil method was used to measure the thermal neutron injection rate in the single crystal silicon irradiation channel 2, and the relationship between the thermal neutron injection rate of the single crystal silicon and the position of the core control rod was obtained. At the same time, the output current of the vanadium self-powered detector was measured, and the relationship between the output current of the vanadium self-powered detector and the position of the core control rod was obtained. Based on the above two data, the least square fitting relationship between the calibration coefficient of the vanadium self-powered detector and the position of the core control rod was determined:

[0050]

[0051] Where F is the scale factor, I is the current output by the vanadium self-powered detector, φ Si It represents the thermal neutron injection rate of the single crystal silicon irradiation channel 2.

[0052] Thus, the calibration of the vanadium self-powered detector is completed, and the actual thermal neutron injection rate of the single crystal silicon in the single crystal silicon irradiation channel can be determined according to the output current of the vanadium self-powered detector.

[0053] Step f): During the single crystal silicon neutron irradiation production stage, a vanadium self-powered detector is used to monitor the thermal neutron flux rate received by the single crystal silicon in real time, thereby accurately determining the cumulative thermal neutron flux of the single crystal silicon.

[0054] Another embodiment of the present invention provides a single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector. The system structure is as follows: Figure 2 As shown, it includes: a vanadium self-powered detector 6 installed in a self-powered detector installation position 3, a signal processor 8, a human-machine terminal 9 and a signal transmission cable 7 for signal transmission.

[0055] The self-powered detector installation position 3 is determined by the single crystal silicon neutron irradiation monitoring method based on the vanadium self-powered detector provided in the above embodiment, and is set in an area around the single crystal silicon irradiation channel 2 where the difference in thermal neutron injection rate does not exceed 10%. The vanadium self-powered detector 6 is installed in the self-powered detector installation position 3. The signal transmission cable is connected to the vanadium self-powered detector 6, and can transmit the electrical signal of the vanadium self-powered detector 6 to the signal processor 8, so that the signal processor 8 can convert the electrical signal into the actual thermal neutron injection rate received by the single crystal silicon 5 placed in the single crystal silicon irradiation channel 2 according to the scale factor determined in the above embodiment, and then output the real-time thermal neutron injection rate and the cumulative thermal neutron injection result to the human-machine terminal 9.

[0056] The single crystal silicon neutron irradiation monitoring method based on the vanadium self-powered detector provided in the embodiment of the present invention can effectively overcome the shortcomings of the rhodium self-powered neutron detector such as low burnup rate and long burnup life, and can realize online monitoring of the neutron injection of single crystal silicon irradiation. At the same time, the high-precision Monte Carlo modeling and analysis technology of the whole core of the research reactor can accurately obtain the thermal neutron injection rate of the irradiation channel position of the heavy water reflector layer area at different fuel cycles and different burnup depths. The vanadium self-powered detector of the present invention is arranged in the neutron detector channel around the single crystal silicon irradiation channel, and the neutron detector is isolated from the strong radiation medium of the research reactor through the channel, which effectively overcomes technical difficulties such as maintenance and replacement. In the single crystal silicon neutron irradiation test stage, the relationship between the vanadium self-powered detector calibration factor and the core state is obtained, and the calibration factor is used to obtain the single crystal silicon irradiation neutron injection in the single crystal silicon neutron irradiation production stage, which effectively improves the hit rate of the single crystal silicon neutron irradiation target resistivity.

[0057] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the method steps involved, and the combination of the implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector, characterized in that: The following steps are involved: Step a): establishing a fuel assembly burnup model for a research reactor used for single crystal silicon neutron irradiation treatment, and calculating the corresponding relationship between the burnup depth and the nuclide composition of the fuel assembly; Step b): establishing a core model of the research reactor, and calculating the corresponding relationship between the axial burnup distribution of the fuel assembly and the fuel cycle and burnup depth according to the calculation result of step a); Step c): establishing an irradiation channel model of the research reactor, coupling the irradiation channel model with the core model and the heavy water reflector, and calculating the corresponding relationship between the irradiation channel thermal neutron injection rate and the burnup cycle and burnup depth; Step d): Calculate the area whose difference from the thermal neutron fluence rate in the irradiation channel does not exceed a given threshold as the detector installation area; Step e): providing a vanadium self-powered detector, installing the vanadium self-powered detector in the detector installation area, installing an activated foil in the irradiation channel, adjusting the rod position of the control rod of the research reactor, using the activated foil to measure the corresponding relationship between the rod position of the control rod and the thermal neutron flux rate in the irradiation channel, and then obtaining the output signal intensity of the vanadium self-powered detector and the calibration coefficient of the thermal neutron flux rate in the irradiation channel, and completing the calibration of the vanadium self-powered detector; Step f): performing single crystal silicon irradiation treatment and using the vanadium self-powered detector to monitor the thermal neutron injection rate of the single crystal silicon.

2. The method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector according to claim 1, characterized in that: In the step b), the core model is calculated using an adaptive grid in the axial direction.

3. The method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector according to claim 1, characterized in that: In the step c), a Monte Carlo program is used for modeling and calculation.

4. The method for monitoring single crystal silicon neutron irradiation based on vanadium self-powered detector according to claim 3, characterized in that: In the step c), based on the calculation results of the steps a) and b), the axial nuclide nucleon density distribution of the fuel assembly is obtained by using the Lagrange interpolation method as material information input into the Monte Carlo program.

5. The method for monitoring single crystal silicon neutron irradiation based on vanadium self-powered detector according to claim 1, characterized in that: In the step d), the given threshold does not exceed 10%.

6. The method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector according to claim 1 or 5, characterized in that: In the step d), calculation is performed within a given radius around the irradiation channel to determine the detector installation area.

7. The method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector according to claim 6, characterized in that: In the step e), at least two vanadium self-powered detectors are installed around each irradiation channel.

8. The method for monitoring single crystal silicon neutron irradiation based on vanadium self-powered detector according to claim 7, characterized in that: In the step e), at least one vanadium self-powered detector is installed on both sides of the line connecting the center of the irradiation channel and the center of the research reactor core.

9. The method for monitoring single crystal silicon neutron irradiation based on a vanadium self-powered detector according to claim 1 or 5, characterized in that: In the step e), the scale coefficient is calculated by least square fitting.

10. A single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector, characterized in that: The single crystal silicon neutron irradiation monitoring system based on vanadium self-powered detector is used for the single crystal silicon neutron irradiation monitoring method based on vanadium self-powered detector according to any one of claims 1 to 9, and comprises Vanadium self-powered detectors, signal transmission cables and signal processors; The vanadium self-powered detector monitors the thermal neutron fluence rate in the detector installation area and transmits the electrical signal to the signal processor through the signal transmission cable. The signal processor calculates and outputs the thermal neutron fluence rate in the corresponding irradiation channel according to the scale factor.

Images