Neutron poison monitoring apparatus

Abstract

Provided in the present disclosure is a neutron poison monitoring apparatus. The neutron poison monitoring apparatus comprises: a container, which is used for accommodating a liquid to be tested that contains a neutron poison; a neutron source, which is configured to emit neutrons to said liquid; a detector, which is configured to detect the number of neutrons and / or the number of photons in said liquid; a multi-channel scaler, which is configured to send to a neutron poison monitoring control apparatus the number of neutrons and / or the number of photons detected by the detector; the neutron poison monitoring control apparatus, which is configured to control the neutron source to emit the neutrons to said liquid, control the detector to detect the number of neutrons or the number of photons in said liquid within a time range after the neutron source is controlled to stop emitting neutrons to said liquid, so as to obtain a plurality of detection values, use a background value to correct each detection value among the plurality of detection values, so as to obtain a plurality of corrected values, and use the plurality of corrected values to determine the concentration of the neutron poison in said liquid; and a shielding device, which is configured to shield external interference received by said liquid and the detector.

Description

Neutron poisoning monitoring device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on and claims priority to an application with CN application number 202311810626.4 and filing date December 26, 2023. The disclosure content of this CN application is hereby incorporated into this disclosure as a whole. Technical Field

[0003] The present disclosure relates to the field of detection, and in particular to a neutron poisoning monitoring device. Background Art

[0004] Traditionally, there are two approaches to detecting neutron poison concentrations: titration and online instrumentation. The titration method requires manual sampling, which carries the risk of radioactive contamination to workers. The test results also have a time lag and lack continuity, but are relatively accurate. The instrumentation method uses online measurement, enabling continuous boron concentration measurement without lag. Summary of the Invention

[0005] In a first aspect of the present disclosure, a neutron poisoning monitoring device is provided, comprising: a container for accommodating a test liquid containing a neutron poison; a neutron source configured to emit neutrons into the test liquid; a detector configured to detect the number of neutrons and / or photons in the test liquid; a multi-channel calibrator configured to transmit the number of neutrons and / or photons detected by the detector to the neutron poisoning monitoring control device; the neutron poisoning monitoring control device configured to control the neutron source to emit neutrons into the test liquid, and control the detector to detect the number of neutrons or photons in the test liquid in each of a plurality of specified time periods within a specified time range after the neutron source is controlled to stop emitting neutrons into the test liquid to obtain a plurality of detection values, correct each of the plurality of detection values ​​using a background value to obtain a plurality of corrected values, and determine the neutron poisoning concentration in the test liquid using the plurality of corrected values; and a shielding device configured to shield the test liquid and the detector from external interference.

[0006] In some embodiments, the neutron poisoning monitoring and control device is configured to control the detector to detect the number of neutrons and / or photons in the liquid to be tested when the liquid to be tested does not include neutrons emitted by the neutron source, so as to measure the background value using the detection results.

[0007] In some embodiments, the neutron poisoning monitoring and control device is configured to control the detector to detect the number of neutrons and / or photons in the liquid to be tested multiple times within the background measurement time period to obtain multiple background detection values, and calculate the average value of the multiple background detection values ​​to obtain the background value.

[0008] In some embodiments, the neutron poisoning monitoring and control device is configured to control the neutron source to delay for a specified period of time after emitting a neutron pulse to the liquid to be tested, and after the delay for the specified period of time and before controlling the neutron source to emit the next neutron pulse to the liquid to be tested, control the detector to detect the number of neutrons and / or photons in the liquid to be tested multiple times to obtain multiple background detection values, and calculate the average value of the multiple background detection values ​​to obtain the background value.

[0009] In some embodiments, the specified time period is a predetermined multiple of the neutron lifetime.

[0010] In some embodiments, the predetermined multiple is not less than 10.

[0011] In some embodiments, the neutron poisoning monitoring and control device is configured to calculate a logarithmic value of each of the multiple correction values ​​to obtain multiple logarithmic values, perform linear fitting on the multiple logarithmic values ​​to obtain a slope of a fitting curve, and determine the neutron poisoning concentration based on the absolute value of the slope.

[0012] In some embodiments, the absolute value of the slope is linearly related to the neutron poison concentration.

[0013] In some embodiments, among the multiple specified time periods, time period 0 is the time period when the neutron source stops emitting neutrons to the liquid to be tested, or is the time period delayed for a specified period of time after the neutron source stops emitting neutrons to the liquid to be tested.

[0014] In some embodiments, the detector includes at least one of a neutron detector and a gamma detector; or, the detector is a detector that detects neutrons and gamma photons simultaneously.

[0015] In some embodiments, the detector is a counting detector or an energy spectrum detector.

[0016] In some embodiments, the neutron source is a photoneutron source based on an electron linear accelerator, or a pulsed neutron source based on a neutron tube.

[0017] Other features and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] FIG1 is a schematic structural diagram of a neutron poisoning monitoring device according to an embodiment of the present disclosure;

[0020] FIG2 is a schematic diagram of a measurement cycle for measuring background values ​​according to an embodiment of the present disclosure;

[0021] FIG3 is a schematic diagram of detection values ​​changing over time according to an embodiment of the present disclosure;

[0022] FIG4 is a schematic diagram of a calibration curve of neutron poison concentration according to an embodiment of the present disclosure;

[0023] FIG5 is a schematic structural diagram of a neutron poisoning monitoring device according to another embodiment of the present disclosure;

[0024] FIG6 is a schematic structural diagram of a neutron poisoning monitoring device according to another embodiment of the present disclosure;

[0025] FIG7 is a schematic structural diagram of a neutron poisoning monitoring device according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present disclosure and its application or use. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure.

[0027] Unless specifically stated otherwise, the relative arrangement of components and steps, the numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present disclosure.

[0028] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0029] Technologies, methods and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods and equipment should be considered part of the authorization specification.

[0030] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0031] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0032] The inventors noted that conventional neutron poison concentration detection techniques assume that the background effect on detection results is stable or even negligible. This results in poor measurement accuracy when the background effect changes. For example, in the field of spent fuel processing, when monitoring neutron poison concentrations, the background is non-negligible and background counts vary over time, making existing solutions incapable of producing accurate monitoring results.

[0033] Accordingly, the present disclosure provides a neutron poisoning monitoring device that uses background data to correct the detection value obtained by the detector, thereby obtaining accurate monitoring results.

[0034] Figure 1 is a schematic diagram of the structure of a neutron poisoning monitoring device according to one embodiment of the present disclosure. As shown in Figure 1 , the neutron poisoning monitoring device includes a neutron poisoning monitoring and control device 11, a container 13 for holding a test liquid 12, a neutron source 14, a detector 15, a multi-channel calibrator 16, and a shielding device 17. The test liquid 12 contains neutron poison.

[0035] The neutron source 14 is configured to emit neutrons toward the liquid 12 to be tested.

[0036] In some embodiments, the neutron source 14 is a photoneutron source based on an electron linear accelerator, a pulsed neutron source based on a neutron tube, or other forms of pulsed neutron sources.

[0037] For example, the width of the neutron pulse generated by the pulsed neutron source is between 0.5 and 4 μs, and the pulse frequency is in the range of 100 to 1000 Hz.

[0038] For example, the neutron poison is boron, cadmium, samarium or other well-known neutron poison elements.

[0039] It should be noted here that, since the present disclosure requires detection of the time spectrum of neutrons or gamma particles, the neutron source needs to transmit neutrons intermittently. In this case, an isotope neutron source that continuously transmits neutrons cannot be used.

[0040] The detector 15 is configured to detect the number of neutrons or photons in the liquid 12 to be tested.

[0041] In some embodiments, the detector 15 includes at least one of a neutron detector and a gamma detector. Alternatively, the detector 15 is a detector that detects neutrons and gamma photons simultaneously.

[0042] In some embodiments, the detector 15 is a counting detector or an energy spectrum detector.

[0043] The multi-channel calibrator 16 is configured to send the number of neutrons or photons detected by the detector 15 to the neutron poisoning monitoring and control device 11 .

[0044] The shielding device 17 is configured to shield the liquid 12 to be measured and the detector 15 from external interference.

[0045] For example, the shielding device 17 includes a neutron shielding device and a photon shielding device.

[0046] The neutron poisoning monitoring and control device 11 is configured to control the neutron source 14 to emit neutrons to the liquid to be tested 12. Within a specified time range after the neutron source 14 is controlled to stop emitting neutrons to the liquid to be tested 12, the detector 15 is controlled to detect the number of neutrons or photons in the liquid to be tested 12 in each specified time period of multiple specified time periods to obtain multiple detection values ​​(i.e., time spectra), and each of the multiple detection values ​​is corrected using the background value to obtain multiple corrected values, and the neutron poisoning concentration in the liquid to be tested 12 is determined using the multiple corrected values.

[0047] It's important to note that the concentration of neutron poisoning can be determined by measuring the temporal variation of neutron counts obtained by a neutron detector, or by measuring the temporal variation of gamma photon counts obtained by a photon detector. According to neutron nuclear reaction theory, the number of gamma photons generated by neutron-matter reactions is proportional to the neutron flux; that is, the gamma photon count is proportional to the neutron count. Therefore, neutron poisoning concentration can also be determined by using gamma photon counting.

[0048] In some embodiments, among the multiple specified time periods, time period 0 is the time period when the neutron source stops emitting neutrons into the liquid to be tested, or is the time period of a specified delay after the neutron source stops emitting neutrons into the liquid to be tested, N0 is the number of neutrons and / or photons detected in time period 0, and N(t) is the number of neutrons and / or photons detected in time period t, where 1≤t≤T, and T is the maximum time period. For example, in the case of a pulsed neutron source, T can be a time period immediately before the next neutron pulse is emitted, or can be a moment immediately before the next neutron pulse is emitted.

[0049] It should be noted that for a period of time after the controlled neutron source stops emitting neutrons into the test liquid, for example, after the pulse ends, the neutron and gamma photon counts follow a negative exponential decay pattern. Fast neutrons generated by the neutron source undergo two primary processes upon entering and being absorbed by the test liquid.

[0050] 1) Energy loss through inelastic scattering or elastic scattering: After entering the liquid to be measured, the fast neutrons (e.g., in the MeV energy range) generated by the neutron source will undergo inelastic or elastic scattering with the nuclides in the liquid, rapidly losing energy and thus leaving the fast neutron region and entering the slow neutron region.

[0051] 2) Neutron Diffusion and Absorption: After entering the slow neutron region, the neutron's movement through the medium can be considered a diffusion process. At the end of the neutron diffusion process, the neutron is absorbed by various nuclides in the liquid. The neutron absorption cross section σ is inversely proportional to the neutron's velocity v, hence the term "1 / v region."

[0052] In the 1 / v region, the probability of a neutron being absorbed in any time segment is constant, which allows the survival probability of a neutron in this process to be expressed using the exponential decay law:

[0053] In formula (1), N0 is the number of neutrons in the liquid during time period 0, N(t) is the number of neutrons during time period t, and τ is the lifetime of the neutrons in the liquid.

[0054] Since process 1) is very short, ranging from nanoseconds to tens of nanoseconds, while process 2) often takes on the order of 10 microseconds, the time taken by process 1) is negligible relative to the entire process. The neutron's lifetime in the liquid being measured, or its survival time, is primarily determined by process 2). In process 2), the neutron's lifetime, τ, is determined by the following formula:

[0055] Among them, t0 represents the time when the neutron enters the liquid to be tested, t c represents the time it takes for the neutron to be absorbed, represents the average value of the two time differences measured experimentally, which is equal to the neutron lifetime τ. n represents the number of nuclides in the liquid, n i represents the number density of nuclide i (1 / cm 3 ), σ 0,i represents the neutron absorption cross section of the nuclide at 25.3 meV energy, and v0 is the velocity of the 25.3 meV neutron, which is 2.2×10 5cm / s. Since the neutron poison element has a huge cross section, its proportion in the denominator on the right side of formula (2) is significant. Therefore, the change in the concentration of the neutron poison element in the liquid will significantly affect the size of τ, and the measurement of the neutron poison element concentration can be achieved by analyzing τ.

[0056] Taking the reciprocal of both sides of formula (8), we get:

[0057] Using a similar analysis as before, Σ 0，a (Thermal neutron macroscopic absorption cross section) can be considered to come from neutron poisons and other elements, while the thermal neutron macroscopic absorption cross section of other elements is almost unchanged, so The value of is linearly related to the concentration of neutron poison.

[0058] Taking the logarithm of both sides of formula (1), we get:

[0059] From formula (4), we can see that on the semi-logarithmic graph, the number of neutrons and time are linearly related, and the absolute value of the linear slope is the inverse of the neutron lifetime. Therefore, the curve of neutron count variation with time (time spectrum curve) is measured, and the slope is obtained by linear fitting after taking the logarithm. The absolute value of this slope is linearly related to the neutron poison concentration value.

[0060] Considering that the neutron poisoning monitoring device may be operated in an environment where the background influence is large and the background value changes slowly, the neutron poisoning monitoring device must take the background count N into consideration. bkg The impact on the measurement is achieved by measuring the background value and deducting it from the detection value obtained by the detector.

[0061] In some embodiments, the neutron poisoning monitoring and control device is configured to control the detector to detect the number of neutrons and / or photons in the liquid to be tested, when the liquid to be tested does not contain neutrons emitted by the neutron source, so as to measure the background value using the detection results. For example, the following embodiments 1 and 2 can be used to measure the background value.

[0062] Example 1

[0063] During the background measurement period, the neutron poisoning monitoring and control device controls the detector to repeatedly detect the number of neutrons in the test liquid to obtain multiple background detection values. It should be noted that during the background measurement period, the test liquid does not include neutrons emitted by the neutron source. Next, the average of these multiple background detection values ​​is calculated to obtain the background value.

[0064] For example, a measurement cycle is divided into a background measurement time period and a beam-out measurement time period. A background value is measured during the background measurement time period. During the beam-out measurement time period, a neutron source is controlled to emit neutrons into a liquid to be measured. Within a specified time range after the neutron source stops emitting neutrons into the liquid to be measured, a detector is controlled to detect the number of neutrons in the liquid to be measured in each of a plurality of specified time periods to obtain a plurality of detection values. Each detection value is then corrected using the obtained background value to obtain a plurality of corrected values.

[0065] Example 2

[0066] As shown in Figure 2, after controlling the neutron source to emit a neutron pulse to the liquid to be tested, the neutron poisoning monitoring and control device delays for a specified time period T1. The specified time period T1 is a predetermined multiple of the neutron lifetime, which is not less than 10.

[0067] For example, when the neutron lifetime does not exceed τ 0 , the specified delay time T1 is 10τ 0 . This specified delay time ensures that the liquid to be tested does not contain neutrons emitted by the neutron source.

[0068] After a specified delay of time T1 and before the neutron poisoning monitoring and control device controls the neutron source to emit the next neutron pulse into the liquid under test, such as during time T2 in Figure 2, the neutron poisoning monitoring and control device controls the detector to detect the number of neutrons in the liquid under test multiple times to obtain multiple background detection values. The background value is obtained by calculating the average of the multiple background detection values.

[0069] It should be noted that the background counts due to background radioactivity have a white noise spectrum in their temporal distribution. Therefore, the background counts can be calculated as the average value of the time channels (the channels in MCS (multichannel scaling) represent a time interval).

[0070] In some embodiments, the neutron poisoning monitoring and control device is configured to calculate a logarithmic value for each of the plurality of correction values ​​to obtain a plurality of logarithmic values. For example, the logarithmic values ​​may be natural logarithmic values. Subsequently, a linear fit is performed on the plurality of logarithmic values ​​to obtain a slope of the fitted curve, and the neutron poisoning concentration is determined based on the absolute value of the slope.

[0071] It should be noted here that, since the absolute value of the slope is linearly related to the neutron poison concentration, the neutron poison concentration can be determined based on the absolute value of the slope.

[0072] For example, for different neutron poison concentrations, each detection value is first corrected using the obtained background value to obtain multiple corrected values. Next, the natural logarithm of each of the multiple corrected values ​​is calculated according to formula (4). In this case, a schematic diagram of the change of detection values ​​over time is shown in Figure 3. Next, a linear fit is performed on the multiple natural logarithm values ​​to obtain the slope of the fitted curve, and the neutron poison concentration is then determined based on the absolute value of the slope, as shown in Figure 4.

[0073] As can be seen from FIG. 4 , by adopting the above-mentioned embodiment of the present disclosure, the concentration of neutron poison can be accurately measured.

[0074] In addition, it should be noted that since the amount of time spectrum statistics is and Therefore, the statistic is essentially a differential signal. This differential characteristic reduces the requirement for neutron source stability, and the actual detection device does not need to detect the intensity fluctuation of the neutron source.

[0075] FIG5 is a schematic diagram of the structure of a neutron poisoning monitoring device according to another embodiment of the present disclosure. FIG5 differs from FIG1 in that, in the embodiment shown in FIG5 , the detector 15 only includes a photon detector 151 , and the shielding device 17 includes a neutron shielding device 171 and a photon shielding device 172 .

[0076] FIG6 is a schematic structural diagram of a neutron poisoning monitoring device according to another embodiment of the present disclosure. FIG6 differs from FIG5 in that, in the embodiment shown in FIG6 , the detector 15 only includes a neutron detector 152 .

[0077] FIG7 is a schematic structural diagram of a neutron poisoning monitoring device according to another embodiment of the present disclosure. FIG7 differs from FIG6 in that, in the embodiment shown in FIG7 , the detector 15 includes a photon detector 151 and a neutron detector 152 .

[0078] By implementing the above-mentioned embodiments of the present disclosure, the concentration of neutron poisons can be accurately measured online in an environment with a high background value, thereby providing an effective measurement solution for online monitoring of neutron poison concentration in nuclear devices.

[0079] The device provided by the present disclosure effectively solves the need to measure the concentration of neutron poisons in nuclear devices, and is of great significance for ensuring the criticality safety of nuclear devices.

[0080] In some embodiments, the functional units described above may be implemented as general-purpose processors, programmable logic controllers (PLC), digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or any appropriate combination thereof, for performing the functions described in the present disclosure.

[0081] Those skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware, or by a program to instruct the relevant hardware, and the program may be stored in a computer-readable storage medium, which may be a read-only memory, a disk, or an optical disk, etc.

[0082] The description of the present disclosure is provided for purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the disclosed form. Many modifications and variations will be apparent to those skilled in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present disclosure and to enable those skilled in the art to understand the present disclosure and design various embodiments with various modifications suitable for specific applications.

Claims

1. A neutron poison monitoring device, comprising: A container for containing a liquid to be measured including a neutron poison; A neutron source configured to emit neutrons towards the liquid to be measured; A detector configured to detect the number of neutrons and / or photons in the liquid to be measured; A multi-channel scaler configured to send the number of neutrons and / or photons detected by the detector to the neutron poison monitoring control device; A neutron poison monitoring control device configured to control the neutron source to emit neutrons towards the liquid to be measured, and within a specified time range after controlling the neutron source to stop emitting neutrons towards the liquid to be measured, control the detector to detect the number of neutrons or photons in the liquid to be measured in each of a plurality of specified time periods to obtain a plurality of detection values, correct each of the plurality of detection values using a background value to obtain a plurality of corrected values, and determine the neutron poison concentration in the liquid to be measured using the plurality of corrected values; A shielding device configured to shield the liquid to be measured and the detector from external interference.

2. The neutron poison monitoring device according to claim 1, wherein The neutron poison monitoring control device is configured to control the detector to detect the number of neutrons and / or photons in the liquid to be measured when the liquid to be measured does not include neutrons emitted by the neutron source, so as to measure the background value using the detection result.

3. The neutron poison monitoring device according to claim 2, wherein The neutron poison monitoring control device is configured to control the detector to detect the number of neutrons and / or photons in the liquid to be measured multiple times within a background measurement time period to obtain a plurality of background detection values, and calculate the average value of the plurality of background detection values to obtain the background value.

4. The neutron poison monitoring device according to claim 2, wherein The neutron poison monitoring control device is configured to control the neutron source to emit a neutron pulse towards the liquid to be measured, delay for a specified duration, and within the specified duration after the delay and before controlling the neutron source to emit the next neutron pulse towards the liquid to be measured, control the detector to detect the number of neutrons and / or photons in the liquid to be measured multiple times to obtain a plurality of background detection values, and calculate the average value of the plurality of background detection values to obtain the background value.

5. The neutron poison monitoring device according to claim 4, wherein The specified duration is a predetermined multiple of the neutron lifetime.

6. The neutron poison monitoring device according to claim 5, wherein The predetermined multiple is not less than 10.

7. The neutron poison monitoring device according to claim 1, wherein The neutron poison monitoring control device is configured to calculate the logarithm of each of the plurality of corrected values to obtain a plurality of logarithm values, perform linear fitting on the plurality of logarithm values to obtain the slope of the fitting curve, and determine the neutron poison concentration according to the absolute value of the slope.

8. The neutron poison monitoring device according to claim 7, wherein The absolute value of the slope has a linear relationship with the neutron poison concentration.

9. The neutron poison monitoring device according to claim 1, wherein Among the multiple specified time periods, the 0 time period is the time period when the neutron source stops emitting neutrons to the liquid to be measured, or the time period after the neutron source stops emitting neutrons to the liquid to be measured and delays for a specified duration.

10. The neutron poison monitoring device according to any one of claims 1-9, wherein the detector includes at least one of a neutron detector and a γ detector; or the detector is a detector that simultaneously detects neutrons and γ photons.

11. The neutron poison monitoring device according to claim 10, wherein the detector is a counting type detector or an energy spectrum type detector.

12. The neutron poison monitoring device according to any one of claims 1-9, wherein the neutron source is an optical neutron source based on an electron linear accelerator or a pulsed neutron source based on a neutron tube.

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