Method and system for monitoring neutron irradiation in monocrystalline silicon based on vanadium self-powered detector

Abstract

The application discloses a kind of single crystal silicon neutron irradiation monitoring method and system based on vanadium self-powered detector, belong to nuclear engineering field.Therein, single crystal silicon neutron irradiation monitoring method based on vanadium self-powered detector includes the following steps: the corresponding relationship of burnup depth and fuel assembly nuclear composition and the corresponding relationship of axial burnup distribution of fuel assembly and fuel cycle, burnup depth are calculated, and then the corresponding relationship of irradiation channel thermal neutron fluence and burnup cycle, burnup depth is calculated;With the position of irradiation channel thermal neutron fluence not more than given threshold as detector installation area, the corresponding relationship of vanadium self-powered detector signal and irradiation channel thermal neutron fluence installed in detector installation area is calibrated using activated foil, so as to monitor single crystal silicon thermal neutron fluence using vanadium self-powered detector.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nuclear engineering, and particularly relates to a single crystal silicon neutron irradiation monitoring method and system based on a vanadium self-powered detector. BACKGROUND

[0002] Neutron 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 and nuclear physics testing. In order to ensure that the resistivity of single crystal silicon after neutron irradiation reaches the target value accurately, it is necessary to accurately control the cumulative thermal neutron fluence of single crystal silicon after neutron irradiation. At present, the cumulative thermal neutron fluence of single crystal silicon after neutron irradiation is usually measured by using an activated foil. However, the activated foil measurement method belongs to offline measurement and cannot be used for online monitoring of the thermal neutron fluence rate. Although a rhodium self-powered detector can be used for online monitoring of the thermal neutron fluence, the burnup rate of rhodium is high and the service life is short, which cannot meet the long-term use requirement. The self-powered detector in the irradiation channel is difficult to frequently maintain or replace. The burnup rate of vanadium is low, and as a self-powered detector material, vanadium can have a longer service life. However, 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. The rhodium detector is used to calibrate the vanadium detector, and the vanadium detector continues to work after the rhodium detector fails. However, this technical solution is used for detection of the reactor core power distribution, which is quite different from the working environment of the research reactor irradiation channel, and cannot be applied to online detection of the thermal neutron fluence in the single crystal silicon NTD process. In addition, the detection accuracy after the rhodium detector fails lacks effective guarantee.

[0004] Therefore, it is necessary to provide a single crystal silicon neutron irradiation monitoring method, which has a positive significance for improving the quality of single crystal silicon NTD products. SUMMARY

[0005] The present application aims to provide a single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector, which can accurately and real-timely monitor the thermal neutron fluence rate of single crystal silicon subjected to neutron irradiation treatment. The present application 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 application, a single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector is provided, which comprises the following steps:

[0007] Step a): establishing a fuel assembly burnup model of 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 axial burnup distribution of the fuel assembly and the corresponding relationship between the fuel cycle and the burnup depth according to the calculation result of step a) ;

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

[0010] Step d) : calculating a region where the difference between the thermal neutron fluxes in the irradiation holes does not exceed a given threshold as a detector installation region;

[0011] Step e) : providing a vanadium self-powered detector, installing the vanadium self-powered detector in the detector installation region, installing an activation foil in the irradiation hole, adjusting the rod position of the control rod of the research reactor, measuring the corresponding relationship between the rod position of the control rod and the thermal neutron flux in the irradiation hole by using the activation foil, and further obtaining the output signal intensity of the vanadium self-powered detector and the calibration coefficient of the thermal neutron flux in the irradiation hole, thereby completing the calibration of the vanadium self-powered detector;

[0012] Step f) : performing single crystal silicon irradiation treatment, and monitoring the thermal neutron flux of the single crystal silicon by using the vanadium self-powered detector.

[0013] The method has a vanadium self-powered detector with rich engineering application experience in the application of large advanced non-power water reactors, effectively overcomes the shortcomings of low burnup rate and long burnup life of rhodium self-powered neutron detectors, and can realize online monitoring of the irradiation neutron flux of single crystal silicon.

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

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

[0016] By using full-core Monte Carlo high-precision modeling and analysis technology, the thermal neutron fluxes of the heavy water reflector regions at different fuel cycles and different burnup depths can be accurately obtained. The vanadium self-powered detector is arranged in the neutron detector hole around the single crystal silicon irradiation hole, and the neutron detector is isolated from the strong radiation medium of the research reactor through the hole, effectively overcoming technical difficulties such as maintenance and replacement. The relationship between the calibration factor of the vanadium self-powered detector and the core state is obtained during the single crystal silicon neutron irradiation test stage, and the single crystal silicon irradiation neutron flux is obtained by using the calibration factor during the single crystal silicon neutron irradiation production stage, effectively improving the hit rate of the single crystal silicon neutron irradiation target resistivity.

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

[0018] Further, in some embodiments, in step d), the given threshold value is not more than 10%.

[0019] Further, in some embodiments, in step d), the calculation is performed within a given radius range on the side of the irradiation channel to determine the detector installation area.

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

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

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

[0023] According to another aspect of the embodiments of the present application, a vanadium self-powered detector based single crystal silicon neutron irradiation monitoring system is provided, which is used in the vanadium self-powered detector based single crystal silicon neutron irradiation monitoring method provided in any of the preceding 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 fluence rate of the detector installation area and transmits an electrical signal to the signal processor through the signal transmission cable, and the signal processor calculates and outputs the corresponding thermal neutron fluence rate in the irradiation channel according to the calibration coefficient. BRIEF DESCRIPTION OF DRAWINGS

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

[0025] Figure 2 FIG. 6 is a schematic diagram of a vanadium self-powered detector based single crystal silicon neutron irradiation monitoring system in an embodiment.

[0026] Meaning of reference signs:

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

[0028] The above drawings are intended to explain the present application in detail, so that those skilled in the art can understand the technical concept of the present application, and are not intended to limit the present application. For the sake of brevity, the above drawings only schematically show the structures related to the technical features of the present application, and do not strictly show the complete device and all the details according to the actual proportion. DETAILED DESCRIPTION

[0029] The present application will be further described in detail by specific embodiments in conjunction with the drawings.

[0030] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those skilled in the art will appreciate that embodiments of the present application can be combined with other embodiments in various ways without structural conflict.

[0031] In the description herein, unless otherwise explicitly specified and limited, the technical terms "mount", "connect", "connection" and the like should be understood in a broad sense, for example, can be mechanical connection, can be electrical connection; can be movable connection, or can be fixed connection or integral. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present application according to the specific circumstances.

[0032] In the description herein, the terms indicating the orientation or position relationship such as "upper", "lower", "left", "right", "transverse", "vertical", "height", "length", "width" and the like are intended to accurately describe the embodiments and simplify the description, and are not intended to limit the parts or structures involved to have a specific orientation, to be installed or operated in a specific orientation, and cannot be understood as limiting the embodiments herein.

[0033] In the description herein, 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 number, specific order or primary and secondary relationship of the technical features described. In the description herein, the meaning of "a plurality of" is at least two.

[0034] Single crystal silicon neutron irradiation production is one of the important applications of research reactors. In the process of single crystal silicon neutron irradiation, in order to ensure that the resistivity of single crystal silicon after neutron irradiation reaches the target value accurately, and to improve the hit rate of the target resistivity of single crystal silicon neutron irradiation, the cumulative thermal neutron fluence of single crystal silicon neutron irradiation must be accurately controlled. The traditional method uses activated foil method to measure the cumulative thermal neutron fluence of single crystal silicon neutron irradiation, which belongs to offline measurement method and cannot monitor the change of single crystal silicon irradiation neutron fluence with time online. Some schemes propose to use rhodium self-powered neutron detector to monitor the single crystal silicon irradiation thermal neutron fluence online, which can monitor the change of single crystal silicon irradiation thermal neutron fluence with time in real time. However, the rhodium self-powered neutron detector has high burnup rate and short burnup life, and the service life is usually only a few years, which cannot meet the demand of long-time online measurement of single crystal silicon irradiation neutron fluence. In addition, the rhodium self-powered neutron detector is arranged on the outer wall of the single crystal silicon irradiation hole, and it is difficult to implement maintenance and replacement of the rhodium self-powered neutron detector in the strong radiation environment of the research reactor.

[0035] In order to solve the above problems, an embodiment of one aspect of the present application provides a single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector, which uses a vanadium self-powered detector to monitor the single crystal silicon irradiation thermal neutron fluence online. The vanadium self-powered detector has the characteristics of high measurement accuracy, low burnup rate, long burnup life, etc., and has a service life of ten or even dozens of years, which can meet the demand of long-time online monitoring of single crystal silicon irradiation thermal neutron fluence. At the same time, the vanadium self-powered detector is arranged in the neutron detector hole around the single crystal silicon irradiation hole, and the position of the neutron detector hole is determined by neutron analysis program, so that the deviation of the thermal neutron fluence of the neutron detector hole position and the thermal neutron fluence of the single crystal silicon irradiation hole position is within ±10%. The neutron detector is isolated from the strong radiation medium of the research reactor through the hole, which effectively overcomes the technical problems of maintenance and replacement.

[0036] When the vanadium self-powered detector is arranged in the neutron detector hole around the single crystal silicon irradiation hole, the current signal output by the vanadium self-powered detector cannot directly reflect the thermal neutron fluence rate at the single crystal silicon position, and the vanadium self-powered detector needs to be calibrated and the scale factor needs to be determined. The scale factor is defined as the ratio of the current signal of the vanadium self-powered detector to the thermal neutron fluence rate of the single crystal silicon. In addition, when the state of the research reactor core changes and causes the change of the neutron energy spectrum, due to the difference between the vanadium self-powered detector and the single crystal silicon position, the changes of 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 single crystal silicon irradiation thermal neutron fluence rate can be monitored online, and the hit rate of the target resistivity of single crystal silicon neutron irradiation can be effectively improved.

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

[0038] Step a): Establishing the database of fuel assembly nuclide composition under different burnup depths.

[0039] The Monte Carlo program based on the probability method is used to calculate the nuclide distribution of each type of fuel assembly of the research reactor at each burnup depth, to obtain the correspondence between the burnup depth and the nuclide composition of the fuel assembly, and to form the database of the nuclide composition of the fuel assembly.

[0040] Step b): Carrying out the multi-fuel cycle calculation of the research reactor core.

[0041] The nuclear design program based on the deterministic method is used to model the full core of the research reactor, considering the control rod position under different burnup depths, and the adaptive grid technology is used in the axial direction to complete the multi-fuel cycle calculation of the research reactor, to obtain the axial burnup distribution of each fuel assembly in the full core under different fuel cycles and different burnup depths, and to obtain the correspondence between the axial burnup distribution of the fuel assembly and the fuel cycle and the burnup depth.

[0042] Step c): Establishing the Monte Carlo high-precision model of the research reactor core and carrying out the Monte Carlo high-precision calculation.

[0043] The database of the nuclide composition of the fuel assembly obtained in step a) and the axial burnup distribution of the fuel assembly obtained in step b) are used to obtain the axial nuclide density distribution of each fuel assembly by using the Lagrange interpolation method, to generate the material information required for the Monte Carlo modeling of the full core. At the same time, the Monte Carlo program is used to model the irradiation hole with high precision, to realize the high-precision modeling of the full core coupling the research reactor core region and the heavy water reflector region, as shown in Figure 1 The full core Monte Carlo calculation coupling the research reactor core region and the heavy water reflector region is carried out to accurately obtain the thermal neutron flux at the position of the irradiation hole in the heavy water reflector region under different fuel cycles and different burnup depths. Thus, the correspondence between the thermal neutron flux of the single-crystal silicon irradiation hole 2 and the burnup cycle and the burnup depth is obtained.

[0044] Step d): Determining the installation position of the vanadium self-sufficient energy detector.

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

[0046] In the process of neutron irradiation of monocrystalline silicon, the monocrystalline silicon rotates at a uniform speed around the axis with the storage tank (a device for loading monocrystalline silicon). In order to ensure the accuracy of thermal neutron flux measurement, at least one position on each side of the connecting line a (0° to 180°, 180° to 360°) between the center of the reactor core 1 and the center of the monocrystalline silicon irradiation hole 2 is selected as the installation position 3 of the self-powered detector.

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

[0048] When the state of the research reactor core changes and causes the neutron energy spectrum to change, due to the difference in the positions of the vanadium self-powered detector and the monocrystalline silicon, the changes in the thermal neutron energy spectrum received by the two are different, and therefore a calibration coefficient needs to be introduced for correction. The main factors affecting the neutron energy spectrum at the positions of the vanadium self-powered detector and the monocrystalline silicon include the control rod position, changes in the core load, fuel element burnup, and the burnup of the emitter body of the vanadium self-powered detector. Through analysis, it is found that the calibration coefficient is mainly affected by the control rod position. The technical solution determines the fitting relationship between the calibration factor of the vanadium self-powered detector and the control rod position of the core during the monocrystalline silicon neutron irradiation test phase, and applies the fitting relationship to obtain the calibration factor of the vanadium self-powered detector corresponding to different control rod positions during the monocrystalline silicon neutron irradiation production phase. The specific steps are as follows:

[0049] During the monocrystalline silicon neutron irradiation test phase, the vanadium self-powered detector is transferred to the self-powered detector installation position 3, and the activated foil is loaded into the monocrystalline silicon irradiation hole 2. The thermal neutron flux in the monocrystalline silicon irradiation hole 2 is measured by the activated foil method, and the relationship between the thermal neutron flux of the monocrystalline silicon and the control rod position of the core is obtained. At the same time, the output current of the vanadium self-powered detector is measured, and the relationship between the output current of the vanadium self-powered detector and the control rod position of the core is obtained. Based on the above two data, the least squares fitting relationship between the calibration factor of the vanadium self-powered detector and the control rod position of the core is determined.

[0050]

[0051] wherein F represents the calibration factor, I represents the output current of the vanadium self-powered detector, and φ Si represents the thermal neutron flux of the monocrystalline silicon irradiation hole 2.

[0052] Thus, the calibration of the vanadium self-powered detector is completed, and the actual thermal neutron flux of the monocrystalline silicon in the irradiation hole can be determined according to the output current of the vanadium self-powered detector.

[0053] Step f): during the monocrystalline silicon neutron irradiation production phase, the thermal neutron flux received by the monocrystalline silicon is monitored in real time by the vanadium self-powered detector, so as to accurately determine the cumulative thermal neutron flux of the monocrystalline silicon.

[0054] The embodiment of another aspect of the present application provides a single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector, which has a structure as shown in the figure and comprises a vanadium self-powered detector 6 installed in a self-powered detector installation site 3, a signal processor 8, a man-machine terminal 9 and a signal transmission cable 7 for signal transmission. Figure 2

[0055] The self-powered detector installation site 3 is determined by the single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector provided in the foregoing embodiment, and is arranged in a region around the single crystal silicon irradiation hole 2, in which the difference in thermal neutron fluence rate is not more than 10%. The vanadium self-powered detector 6 is installed in the self-powered detector installation site 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 fluence rate received by the single crystal silicon 5 placed in the single crystal silicon irradiation hole 2 according to the scale factor determined in the foregoing embodiment, and then output the real-time thermal neutron fluence rate and the cumulative thermal neutron fluence result to the man-machine terminal 9.

[0056] The single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector provided by the embodiment of the present application can effectively overcome the shortcomings of low burnup rate and long burnup life of a rhodium self-powered neutron detector, and can realize online monitoring of the single crystal silicon irradiation neutron fluence. Meanwhile, the high-precision modeling analysis technology of the whole core Monte Carlo of a research reactor can be used to accurately obtain the thermal neutron fluence rate at the position of the irradiation hole in the heavy water reflector region at different fuel cycles and different burnup depths. The vanadium self-powered detector of the present application is arranged in the neutron detector hole around the single crystal silicon irradiation hole, and the neutron detector is isolated from the strong radiation medium of the research reactor through the hole, which effectively overcomes the technical difficulties in maintenance and replacement. The relationship between the scale factor of the vanadium self-powered detector and the core state is obtained during the single crystal silicon neutron irradiation test stage, and the single crystal silicon irradiation neutron fluence is obtained by using the scale factor during the single crystal silicon neutron irradiation production stage, which effectively improves the hit rate of the target resistivity of the single crystal silicon neutron irradiation.

[0057] The above embodiments are intended to further illustrate the present application in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present application. Within the scope of the present application, the method steps involved are optimized or equivalently replaced, and the embodiments in different embodiments are combined without structural and principle conflicts, which all fall within the protection scope of the present application.​

Claims

1. A method for monitoring neutron irradiation in monocrystalline silicon based on a self-powered detector with vanadium, characterized by that, The method comprises the following steps: Step a): establishing a fuel assembly burnup model of a research reactor for neutron irradiation of single crystal silicon, and calculating the corresponding relationship between burnup depth and nuclide composition of the fuel assembly; Step b): establishing a core model of the research reactor, and calculating the corresponding relationship between axial burnup distribution of the fuel assembly and fuel cycle, 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 a heavy water reflector, and calculating the corresponding relationship between irradiation channel thermal neutron flux and burnup cycle, burnup depth; Step d): calculating a region where the difference between thermal neutron fluxes in the irradiation channels does not exceed a given threshold as a detector installation region; Step e): providing a vanadium self-powered detector, installing the vanadium self-powered detector in the detector installation region, installing an activation foil in the irradiation channel, adjusting the rod position of a control rod of the research reactor, measuring the corresponding relationship between the rod position of the control rod and the thermal neutron flux in the irradiation channel by using the activation foil, and further obtaining a calibration coefficient of output signal intensity of the vanadium self-powered detector and the thermal neutron flux in the irradiation channel, thereby completing calibration of the vanadium self-powered detector; Step f): performing single crystal silicon irradiation and monitoring the thermal neutron flux of the single crystal silicon by using the vanadium self-powered detector.

2. The method according to claim 1, wherein the vanadium self-powered detector is a single crystal silicon neutron irradiation monitor. In the step b), the core model is calculated in the axial direction by using an adaptive grid.

3. The method of claim 1, wherein the vanadium self-powered detector is a single crystal silicon neutron exposure monitor. In the step c), modeling and calculation are performed by using a Monte Carlo program.

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

5. The method of claim 1, wherein the vanadium-based self-powered detector is a single crystal silicon neutron exposure monitor. In the step d), the given threshold is not more than 10%.

6. The method according to claim 1 or 5, wherein the vanadium self-powered detector is a single crystal silicon neutron irradiation monitor. In the step d), calculation is performed within a given radius range around the irradiation channel to determine the detector installation region.

7. The method according to claim 6, wherein the vanadium self-powered detector is a single crystal silicon neutron radiation monitor. In the step e), at least two vanadium self-powered detectors are installed around each irradiation channel.

8. The method according to claim 7, wherein the vanadium self-powered detector is a single crystal silicon neutron radiation monitor. In the step e), at least one vanadium self-powered detector is installed on each side of a line connecting the center of the irradiation channel and the center of the core of the research reactor.

9. The method according to claim 1 or 5, wherein the vanadium self-powered detector is a single crystal silicon neutron irradiation monitor. In the step e), the calibration coefficient is calculated by using least square fitting.

10. A single-crystal silicon neutron irradiation monitoring system based on a vanadium self-sufficient energy detector, characterized in that, The single crystal silicon neutron irradiation monitoring system based on a vanadium self-powered detector is used in the single crystal silicon neutron irradiation monitoring method based on a vanadium self-powered detector as claimed in any one of claims 1 to 9, and comprises a vanadium self-powered detector, a signal transmission cable, and a signal processor; The vanadium self-powered detector monitors the thermal neutron flux of the detector installation region and transmits an electric signal to the signal processor through the signal transmission cable, and the signal processor calculates and outputs the corresponding thermal neutron flux in the irradiation channel according to the calibration coefficient.

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