γ-β composite detection device

Abstract

The present invention belongs to the field of nuclear power maintenance technology, and specifically relates to a γ-β composite detection device. The absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays, so that the first photomultiplier tube and the first signal processing unit can detect β rays according to the light emitted by the first scintillation crystal, and the absorption rate of the second scintillation crystal to β rays is lower than that to γ ​​rays, so that the second photomultiplier tube and the second signal processing unit can detect γ rays according to the light emitted by the second scintillation crystal, thereby realizing the composite detection of γ and β rays, so as to assist in determining the damage of fuel assemblies at different time of leaving the stack. In addition, the first scintillation crystal is used as a detection chamber, which can effectively store the gas to be tested, and can make the first scintillation crystal more fully receive the irradiation of the rays released by the gas to be tested from the inside to the outside, thereby making the γ-β composite detection device more sensitive to the β rays released by the gas to be tested.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power maintenance, and in particular relates to a gamma-beta composite detection device. Background Art

[0002] The most efficient way to detect damage to nuclear fuel assemblies is to detect radioactive fission gases released to the outside. The fission materials in the fuel assemblies mainly include Xe-133, Kr-85, I-131, Cs-136, Cs-134, CS-137 and isotopes of these elements. Among them, the gaseous fission products that are not easily soluble in water are mainly Xe-133 and Kr-85 and their isotopes. The gamma-ray decay branch ratio of Xe-133 is large, and the detection of gamma rays can find obvious energy characteristic peaks, thereby determining Xe-133 and its radioactive activity. However, due to the short half-life, it is difficult to determine the damage of fuel assemblies that have been out of the reactor for a long time by measuring the Xe-133 nuclide. Kr-85 has a long half-life and can be used as a basis for determining the damage of fuel assemblies that have been out of the reactor for a long time. However, the γ decay branch ratio of Kr-85 is small, and it is difficult to detect obvious energy characteristic peaks through γ rays. β rays are continuous spectra, and it is difficult to conduct quantitative and qualitative analysis of radioactive substances when there are multiple radioactive substances. Therefore, it is necessary to effectively detect the radioactivity of nuclear fuel assemblies that have been out of the reactor for a long time. Summary of the invention

[0003] In order to overcome the problems existing in the related art, a γ-β composite detection device is provided.

[0004] According to one aspect of an embodiment of the present disclosure, a γ-β composite detection device is provided, the γ-β composite detection device comprising: a first photomultiplier tube, a second photomultiplier tube, a first scintillation crystal, a second scintillation crystal, a first signal processing unit, and a second signal processing unit;

[0005] The first scintillation crystal has a chamber inside, the chamber is used to store the gas to be measured, and one side surface of the second scintillation crystal is in close contact with the surface of the first scintillation crystal;

[0006] The incident window of the first photomultiplier tube is in close contact with the surface of the first scintillation crystal;

[0007] The incident window of the second photomultiplier tube is in close contact with the other side surface of the second scintillation crystal;

[0008] The first scintillation crystal emits light when irradiated by β and / or γ rays, the absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays, the first photomultiplier tube generates an electrical signal according to the light emitted by the first scintillation crystal, and the first signal processing unit is connected to the first photomultiplier tube and is used to generate a spectrum for identifying β rays according to the electrical signal generated by the first photomultiplier tube;

[0009] The second scintillation crystal emits light when irradiated with β and / or γ rays, the absorption rate of the second scintillation crystal to β rays is lower than that to γ ​​rays, the second photomultiplier tube generates an electrical signal according to the light emitted by the second scintillation crystal, and the second signal processing unit is connected to the second photomultiplier tube and is used to generate a spectrum for identifying γ rays according to the electrical signal generated by the second photomultiplier tube.

[0010] In a possible implementation manner, the outer wall of the first scintillation crystal is shaped like a sphere, and the inner wall of the chamber of the first scintillation crystal is shaped like a sphere.

[0011] In a possible implementation manner, the sphere formed by the outer wall of the first scintillation crystal is concentric with the sphere formed by the inner wall of the chamber of the first scintillation crystal.

[0012] In a possible implementation, one side surface of the second scintillator crystal is a spherical surface, and the spherical surface is concentric with the sphere formed by the outer wall of the first scintillator;

[0013] The other side surface of the second scintillation crystal is a plane parallel to a cut plane of one side surface of the second scintillation crystal.

[0014] In a possible implementation, the axial section of the second scintillation crystal is a trapezoidal section, the longer base of the trapezoidal section is located on one side surface of the second scintillation crystal, and the shorter base of the trapezoidal section is located on the other side surface of the second scintillation crystal.

[0015] In a possible implementation manner, the first scintillator crystal includes a plastic scintillator.

[0016] In a possible implementation, the second scintillation crystal includes sodium iodide or lanthanum bromide.

[0017] In a possible implementation, the γ-β composite detection device comprises: a gas processing unit;

[0018] The gas processing unit is in communication with the chamber of the first scintillation crystal and is used for processing the gas input into the chamber of the first scintillation crystal.

[0019] In a possible implementation, the gas processing unit includes: an air inlet, a filter, a dryer, a refrigerator, an ion trap, and an air outlet;

[0020] The filter is in communication with the air inlet and is used to filter solid particles, gaseous iodine and gaseous cesium in the gas input from the air inlet;

[0021] The dryer is connected to the filter and is used to filter water vapor of the gas output by the filter;

[0022] The refrigerator is connected to the dryer and is used to cool the gas output from the dryer;

[0023] The ion trap is connected to the refrigerator and is used to filter the charged ions of the gas output by the refrigerator;

[0024] One end of the gas outlet is connected to the ion trap, and the other end of the gas outlet is connected to the chamber. The gas output by the ion trap is input into the chamber through the gas outlet.

[0025] In a possible implementation, the γ-β composite detection device is wrapped with a lead chamber on the outside.

[0026] The beneficial effect of the present invention is that: in the embodiment of the present disclosure, the absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays, so that the first photomultiplier tube and the first signal processing unit can detect β rays according to the light emitted by the first scintillation crystal, and the absorption rate of the second scintillation crystal to β rays is lower than that to γ ​​rays, so that the second photomultiplier tube and the second signal processing unit can detect γ rays according to the light emitted by the second scintillation crystal, thereby realizing the composite detection of γ and β rays, realizing quantitative and qualitative analysis of radioactive gases such as Xe-133 and Kr-85, so as to assist in determining the damage of fuel assemblies at different time of leaving the pile. In addition, using the first scintillation crystal as a detection chamber can not only effectively store the gas to be tested, but also make the first scintillation crystal more fully receive the irradiation of the rays released by the gas to be tested from the inside to the outside, thereby making the γ-β composite detection device more sensitive to detect the β rays released by the gas to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a γ-β composite detection device according to an exemplary embodiment.

[0028] Figure 2 It is a block diagram of a γ-β composite detection device according to an exemplary embodiment. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Generally speaking, fuel assemblies that have been out of the stack for a short time have a higher content of Xe-133 gas. The energy characteristic peak of Xe-133 can be found by detecting gamma rays to analyze its radioactive activity.

[0031] Since the nuclides released from damaged fuel assemblies are mainly: Xe-133, Kr-85, I-131, Cs-136, Cs-134, Cs-137 and isotopes of Xe and Kr, most of the remaining nuclides are medium- and short-lived, and most of them decay within about a week after leaving the reactor. The isotope half-lives of Xe and Kr are generally too short, and they are basically not present in the nuclear fuel assemblies two months after leaving the reactor. The half-life of I-131 is 8.02d, the half-life of Cs-134 is 752.63d, and the half-life of Cs-137 is 11013d. However, the above nuclides are isotopes that are easily soluble in water. Once the fuel assembly is damaged, most of the leaked I-131, Cs-134 and Cs-137 will remain in the coolant. Therefore, for long-term stored fuel assemblies, the most important gaseous nuclide in the gas to be tested is Kr-85. Therefore, for fuel assemblies that have been out of the reactor for a long time, Kr-85 nuclides can be detected. The γ decay branch ratio of Kr-85 is only 0.43%, and it is difficult to detect obvious characteristic peaks. β rays can be detected to analyze Kr-85.

[0032] Figure 1 FIG. 1 is a schematic diagram of a γ-β composite detection device according to an exemplary embodiment. Figure 1 As shown, the γ-β composite detection device may include: a first photomultiplier tube 2, a second photomultiplier tube 3, a first scintillation crystal 5, a second scintillation crystal 4, a first signal processing unit (not shown in the figure), and a second signal processing unit (not shown in the figure);

[0033] The first scintillation crystal 5 has a chamber 6 inside, and the chamber 6 is used to store the gas to be tested. One side surface of the second scintillation crystal 4 is in close contact with the surface of the first scintillation crystal 5. The shapes of the first scintillation crystal 5 and the second scintillation crystal 4 can be any shape, such as a rectangular parallelepiped, a column or a polyhedron. The cavity of the first scintillation crystal 5 can also be any shape, such as a rectangular parallelepiped, a column or a polyhedron. The shapes of the first scintillation crystal 5 and the second scintillation crystal 4 can be the same or different.

[0034] The first scintillation crystal 5 can emit light when irradiated by β and / or γ rays, and the absorption rate of the first scintillation crystal 5 to β rays is higher than that to γ ​​rays. For example, the material of the first scintillation crystal can be a plastic scintillator, and the absorption efficiency of the plastic scintillator to β rays is about 100 times higher than that to γ ​​rays. (The material of the first scintillation crystal is not limited in the embodiment of the present disclosure, as long as the absorption rate of the material to β rays is higher than that to γ ​​rays). The incident window of the first photomultiplier tube 2 is close to the surface of the first scintillation crystal 5. The first photomultiplier tube 2 generates an electrical signal according to the light emitted by the first scintillation crystal 5. The first signal processing unit is connected to the first photomultiplier tube 2. Since the internal fission gas in the fuel assembly with a long discharge time is considered to contain only long-period Kr-85, and Kr-85 mainly releases β rays, in addition, the absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays. In this way, the first signal processing unit can generate a spectrum for identifying β rays according to the electrical signal generated by the first photomultiplier tube. Therefore, the first scintillation crystal, the first photomultiplier tube and the first signal processing unit can be mainly used to detect the beta rays of the fuel assembly with a long out-of-stack time.

[0035] The second scintillation crystal 4 can emit light when irradiated with β and / or γ rays. The absorption rate of the second scintillation crystal 4 to β rays is lower than that to γ ​​rays. For example, the material of the second scintillation crystal can be NaI (sodium iodide), LaBr3 (lanthanum bromide), etc. (the material of the second scintillation crystal is not limited in the embodiment of the present disclosure, as long as the absorption rate of the material to β rays is lower than that to γ ​​rays). The incident window of the second photomultiplier tube 3 is in close contact with the other side surface of the second scintillation crystal 4. The second photomultiplier tube 3 generates an electrical signal according to the light emitted by the second scintillation crystal 4. The second signal processing unit is connected to the second photomultiplier tube 3. Since there are multiple radioactive nuclides releasing gamma rays in the fuel assembly with a short out-of-combustion time, the gamma rays of a specific nuclide have a specific energy value, which can show an obvious peak on the spectrum of the second signal processing unit to confirm which nuclide it is, while the beta rays can only form a continuous graph without a peak, and since the second scintillation crystal has a low absorption efficiency for beta rays and a high absorption efficiency for gamma rays, the measurement signal of the second photomultiplier tube for beta rays can exist as a radioactive background in the measurement signal of the second photomultiplier tube for gamma rays, so that the second signal processing unit can generate a spectrum for identifying gamma rays according to the electrical signal generated by the second photomultiplier tube. Therefore, the second scintillation crystal, the second photomultiplier tube and the second signal processing unit can be mainly used to detect gamma rays for the fuel assembly with a short out-of-combustion time.

[0036] In the disclosed embodiment, the absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays, so that the first photomultiplier tube and the first signal processing unit can detect β rays according to the light emitted by the first scintillation crystal, and the absorption rate of the second scintillation crystal to β rays is lower than that to γ ​​rays, so that the second photomultiplier tube and the second signal processing unit can detect γ rays according to the light emitted by the second scintillation crystal, thereby realizing the composite detection of γ and β rays, realizing the quantitative and qualitative analysis of radioactive gases such as Xe-133 and Kr-85, and thus being able to assist in determining the damage of fuel assemblies at different times of leaving the stack. In addition, using the first scintillation crystal as a detection chamber can not only effectively store the gas to be detected, but also allow the first scintillation crystal to be more fully irradiated by the rays released by the gas to be detected from the inside to the outside, thereby allowing the γ-β composite detection device to more sensitively detect the β rays released by the gas to be detected.

[0037] In a possible implementation, the outer wall of the first scintillation crystal may be spherical, and the inner wall of the chamber of the first scintillation crystal may also be spherical. For example, the sphere formed by the outer wall of the first scintillation crystal is concentric with the sphere formed by the inner wall of the chamber of the first scintillation crystal. In this way, the area of ​​the first scintillation crystal irradiated by radiation can be effectively increased, the sensitivity of the first scintillation crystal in detecting radiation can be increased, and the volume of the gas stored in the chamber can be increased. In an example, the detection efficiency of the first scintillation crystal for β-rays can be increased to more than 50%.

[0038] In a possible implementation, when the first scintillator crystal is spherical in shape, one side surface of the second scintillator crystal can be processed into a spherical surface, and the spherical surface can be concentric with the shape of the first scintillator; the other side surface of the second scintillator crystal is a plane parallel to the cut surface of the one side surface of the second scintillator crystal. In this way, the area of ​​the second scintillator crystal irradiated by radiation can be effectively increased, and the side of the second scintillator crystal that is close to the first scintillator crystal can be more closely fitted with the outer surface of the first crystal, thereby increasing the sensitivity of the second scintillator crystal in detecting radiation.

[0039] In a possible implementation, the axial section of the second scintillation crystal may be a trapezoidal section, wherein the longer base of the trapezoidal section is located on one side surface of the second scintillation crystal, and the shorter base of the trapezoidal section is located on the other side surface of the second scintillation crystal.

[0040] In a possible implementation, the lead chamber 1 can be wrapped around the outside of the first photomultiplier tube 2, the second photomultiplier tube 3, the first scintillation crystal 5, and the second scintillation crystal 4. The lead chamber can shield external radiation rays to further improve the accuracy of detection.

[0041] Figure 2 FIG. 1 is a block diagram of a γ-β composite detection device according to an exemplary embodiment. Figure 2As shown, the γ-β composite detection device may further include: a gas processing unit.

[0042] The gas processing unit is in communication with the chamber of the first scintillation crystal and is used to process the gas introduced into the chamber of the first scintillation crystal;

[0043] like Figure 2 As shown, the gas processing unit may include: an air inlet, a filter, a dryer, a refrigerator, an ion trap, and an air outlet;

[0044] The filter is communicated with the air inlet and is used for filtering solid particles, gaseous iodine and gaseous cesium in the gas input from the air inlet;

[0045] The dryer is connected to the filter and is used to filter water vapor of the gas output by the filter;

[0046] The refrigerator is connected to the dryer to cool the gas coming out of the dryer;

[0047] The ion trap is connected to the refrigerator and is used to filter the charged ions in the refrigerator.

[0048] For example, the gas to be tested enters the detection device from the gas inlet and first reaches the gas processing unit;

[0049] The gas to be tested first passes through a filter in the gas processing unit to filter out solid particles and active gases such as iodine and cesium;

[0050] The gas to be tested passes through the dryer to filter out water vapor and iodine and cesium dissolved in the water vapor, which can effectively avoid the interference of active gases such as iodine and cesium on the test results;

[0051] The gas to be tested passes through the refrigerant, which cools the gas and prepares it for entering the detection unit and further filtering the water vapor in the gas;

[0052] The gas to be tested passes through the ion trap to filter out the charged ions in the gas;

[0053] The gas to be measured enters the detection gas cavity (an example of the cavity of the first scintillation crystal), and the γ detector (an example of the first scintillation crystal and the first photomultiplier tube) and the β detector (an example of the first scintillation crystal and the first photomultiplier tube) respectively detect the γ rays and β particles in the gas cavity, and the detection signal of the γ detector enters the γ spectrometer (an example of the second signal processing unit) to form a spectrum for identifying the γ rays, and the detection signal of the β detector enters the β signal processing unit to form a spectrum for identifying the β rays.

[0054] If the target is a fuel assembly with a short out-of-combustion time, the energy characteristic peak is analyzed on the gamma spectrum to achieve the analysis of Xe-133 nuclide;

[0055] If the fuel assembly is out of the reactor for a long time, the activity influence of interfering nuclides can be eliminated by detecting the total beta count and assisting the gamma detector to perform energy spectrum analysis, thus achieving quantitative analysis of Kr-85.

[0056] Among them, the β signal processing module can adopt an independent functional module design method, which is mainly divided into a power supply module, a data processing module, a VF (voltage-frequency) conversion module, a zero adjustment potentiometer, etc. The radioactive signal processing unit composed of these two parts jointly performs analog signal processing, digital-to-analog conversion, and digital signal processing on the β and γ pulse electrical signals transmitted by the detector to form an analyzable energy spectrum.

[0057] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A γ-β composite detection device, characterized in that: The γ-β composite detection device comprises: a first photomultiplier tube, a second photomultiplier tube, a first scintillation crystal, a second scintillation crystal, a first signal processing unit, and a second signal processing unit; The first scintillation crystal has a chamber inside, the chamber is used to store the gas to be measured, and one side surface of the second scintillation crystal is in close contact with the surface of the first scintillation crystal; The incident window of the first photomultiplier tube is in close contact with the surface of the first scintillation crystal; The incident window of the second photomultiplier tube is in close contact with the other side surface of the second scintillation crystal; The first scintillation crystal emits light when irradiated by β and / or γ rays, the absorption rate of the first scintillation crystal to β rays is higher than that to γ ​​rays, the first photomultiplier tube generates an electrical signal according to the light emitted by the first scintillation crystal, and the first signal processing unit is connected to the first photomultiplier tube and is used to generate a spectrum for identifying β rays according to the electrical signal generated by the first photomultiplier tube; The second scintillation crystal emits light when irradiated with β and / or γ rays, the absorption rate of the second scintillation crystal to β rays is lower than the absorption rate to γ ​​rays, the second photomultiplier tube generates an electrical signal according to the light emitted by the second scintillation crystal, and the second signal processing unit is connected to the second photomultiplier tube and is used to generate a spectrum for identifying γ rays according to the electrical signal generated by the second photomultiplier tube; The outer wall of the first scintillation crystal is shaped like a sphere, and the inner wall of the chamber of the first scintillation crystal is shaped like a sphere; The first scintillator crystal comprises a plastic scintillator; The second scintillation crystal includes sodium iodide or lanthanum bromide.

2. The γ-β composite detection device according to claim 1, characterized in that: The sphere formed by the outer wall of the first scintillation crystal is concentric with the sphere formed by the inner wall of the chamber of the first scintillation crystal.

3. The γ-β composite detection device according to claim 1, characterized in that: One side surface of the second scintillation crystal is a spherical surface, and the spherical surface is concentric with the sphere formed by the outer wall of the first scintillation crystal; The other side surface of the second scintillation crystal is a plane parallel to the tangent plane of the one side surface of the second scintillation crystal.

4. The γ-β composite detection device according to claim 1, characterized in that: The axial section of the second scintillation crystal is a trapezoidal section, the longer bottom side of the trapezoidal section is located on one side surface of the second scintillation crystal, and the shorter bottom side of the trapezoidal section is located on the other side surface of the second scintillation crystal.

5. The γ-β composite detection device according to claim 1, characterized in that: The γ-β composite detection device further comprises: a gas processing unit; The gas processing unit is in communication with the chamber of the first scintillation crystal and is used for processing the gas input into the chamber of the first scintillation crystal.

6. The γ-β composite detection device according to claim 5, characterized in that: The gas processing unit comprises: an air inlet, a filter, a dryer, a refrigerator, an ion trap and an air outlet; The filter is in communication with the air inlet and is used to filter solid particles, gaseous iodine and gaseous cesium in the gas input from the air inlet; The dryer is connected to the filter and is used to filter water vapor of the gas output by the filter; The refrigerator is connected to the dryer and is used to cool the gas output from the dryer; The ion trap is connected to the refrigerator and is used to filter the charged ions of the gas output by the refrigerator; One end of the gas outlet is connected to the ion trap, and the other end of the gas outlet is connected to the chamber. The gas output by the ion trap is input into the chamber through the gas outlet.

7. The γ-β composite detection device according to claim 1, characterized in that: The outer side of the γ-β composite detection device is wrapped with a lead chamber.

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