JP7480004B2 - Nuclear material measurement system and method for measuring nuclear material - Google Patents

Description

The present invention relates to a nuclear material measurement system and a method for measuring nuclear material.

A conventional method for detecting and measuring fissile materials involves irradiating a measurement object with pulsed fast neutrons and measuring the change over time in the production rate of fission neutrons produced by the reaction (nuclear fission reaction) between the fast neutrons and the neutrons whose energy has been slowed down by the measurement object and the fissile material, based on the time of irradiation of the pulsed fast neutrons.

According to Patent Document 1, fission neutrons generated by a fission reaction exponentially decay with a certain time constant (annihilation time). This annihilation time depends on the neutron absorption and moderation characteristics of the material contained in the measurement object, and the total count number of fission neutrons measured by a neutron detector is proportional to the amount of fissionable material and changes depending on the neutron absorption and moderation characteristics of the material contained in the measurement object. Therefore, a calibration test is performed in advance to change the physical property values that indicate the neutron absorption and moderation performance of the material contained in the measurement object, and the relationship between the annihilation time and the total count number of fission neutrons detected in a state in which a known amount of known fissionable material is contained is obtained. This is a method for deriving the amount of unknown fissionable material in the measurement object based on this relationship.

Patent Document 2 proposes a method for measuring fissile material in fuel debris using an X-ray CT scanner. This method measures the amount of nuclear material by correcting the results of gamma-ray measurements of nuclear material in damaged or melted nuclear fuel or nuclides that behave in a similar manner with the results of density measurements made by X-ray CT.

Patent Document 3 proposes a system that combines X-ray CT, photonuclear reactions, the use of photoneutron mixed rays, and neutron activation analysis using an electron linear accelerator and an X-ray generating converter.

Patent Document 4 discloses a nuclear material quantity measurement device that includes an X-ray CT device that irradiates the measurement object with two or more types of X-rays having different energy ranges and detects the transmitted X-rays, and a neutron measurement device that irradiates the measurement object with a neutron beam and counts the number of neutrons emitted from the measurement object.

Patent No. 6179885 Patent No. 6468931 Patent No. 4649580 JP 2020-94906 A

In the method of Patent Document 1, if there is no database of physical property values that indicate the neutron absorption and moderation performance of the material contained in the measurement object, it is not possible to derive the amount of fissile material. In particular, at the Fukushima Daiichi Nuclear Power Plant, it is assumed that the fissile material in the fuel assemblies is in a molten state, and that the structural material, neutron absorbing material, and concrete material are mixed together, making it difficult to build in advance a database of physical property values that indicate the neutron absorption and moderation performance of the material contained in the measurement object.

In the method of Patent Document 2, even if density correction is performed using X-ray CT, it is difficult to directly measure fissile materials because the energy of gamma rays from fissile materials is low.

In the method of Patent Document 3, it is difficult to measure fissile materials using only density distribution information in X-ray CT, and although it is possible to measure difficult-to-measure nuclides such as iodine-129 in photonuclear reactions, it is difficult to measure fissile materials. When using photoneutron mixed radiation, it is difficult to distinguish and measure neutrons produced in photonuclear reactions from those produced by neutron-induced fission reactions, so it is difficult to measure fissile materials. With neutron activation analysis, it is possible to measure the content of chlorine, lead, etc., but it is still difficult to measure fissile materials.

In the nuclear material quantity measurement device described in Patent Document 4, a transport mechanism is provided between the X-ray CT device and the neutron measurement device, and the measurement object is moved to measure the X-rays and neutrons separately. This makes it difficult to standardize the conditions when the measurement object is irradiated with the X-rays and neutrons, and the system becomes large.

It is possible to apply multiple measurement techniques, such as X-ray CT and active neutron analysis, but it is difficult to perform measurements using multiple techniques without changing the electron beam conditions and the target, etc.

As described above, no effective systems or measurement methods have been proposed for detecting and measuring fissile materials in waste and stored materials from nuclear power plants, and in materials containing damaged or melted fuel.

The objective of the present invention is to accurately measure fissile material contained in waste and stored materials from nuclear power plants and in materials containing damaged or melted fuel.

The nuclear material measurement system of the present invention comprises an electron beam accelerator, a target that receives a pulsed high-energy electron beam emitted from the electron beam accelerator and generates pulsed bremsstrahlung and pulsed fast neutrons, a transmission bremsstrahlung detector, and a neutron detector, and is configured to irradiate an object to be measured with pulsed bremsstrahlung and pulsed fast neutrons emitted from the target by irradiation with the same pulsed high-energy electron beam, the transmission bremsstrahlung detector measures the pulsed bremsstrahlung that has penetrated the object to be measured, and the neutron detector measures fast neutrons emitted from the object to be measured by irradiation with pulsed fast neutrons.

The present invention makes it possible to accurately measure the amount of fissile material contained in waste and stored materials from nuclear power plants, as well as materials containing damaged or melted fuel.

1 is a configuration diagram showing an example of a fissile material measurement system according to a first embodiment. 1 is a graph showing an example of the amount of bremsstrahlung radiation produced by electron beam irradiation. 1 is a graph showing an example of a reaction cross section of a reaction that produces one neutron by bremsstrahlung irradiation. 1 is a graph showing an example of changes over time in the intensity of a pulsed high-energy electron beam, the intensity of a pulsed bremsstrahlung, and the intensity of a pulsed fast neutron in Example 1. FIG. 2 is a block diagram showing the nuclear material measurement system of FIG. 1. 4 is a graph showing an example of a pulse-height spectrum of the neutron detector of Example 1. 13 is a graph showing another example of the pulse-height spectrum of the neutron detector according to the first embodiment. 1 is a graph showing an example of a change in fast neutron count rate over time in Example 1. FIG. 11 is a perspective view showing a fissile material measuring system according to a second embodiment. FIG. 10 is a top view of the fissile material measurement system of FIG. FIG. 11 is a perspective view showing a fissile material measuring system according to a third embodiment. FIG. 11 is a perspective view showing a fissile material measuring system according to a fourth embodiment.

The following is a summary of embodiments of the present disclosure.

In a nuclear material measurement system consisting of an electron beam accelerator, an electron beam accelerator control unit, a target for generating pulsed bremsstrahlung and pulsed fast neutrons, a neutron detector, a transmission bremsstrahlung detector, and a data processing and analysis device, pulsed high-speed electrons accelerated by the electron beam accelerator are irradiated onto the target for generating pulsed bremsstrahlung and pulsed fast neutrons.

Here, bremsstrahlung radiation refers to electromagnetic waves (such as X-rays) emitted by the interaction between electrons and a strong electromagnetic field. When a fast-moving charged particle, such as an electron, passes near an atomic nucleus, it is slowed down by the electric field and the energy lost in the process is released. For this reason, it is also called bremsstrahlung X-rays.

By using heavy metals such as gold and lead as targets for generating pulsed bremsstrahlung and pulsed fast neutrons, pulsed bremsstrahlung and pulsed fast neutrons corresponding to the irradiation time and irradiation time width of the pulsed fast electrons are generated. The generated pulsed bremsstrahlung and pulsed fast neutrons are irradiated onto the object to be measured. The pulsed bremsstrahlung that has passed through the object to be measured and attenuated is measured by a transmission bremsstrahlung detector.

A transmission bremsstrahlung detector has detection elements arranged in an array, and measures the intensity distribution of transmission bremsstrahlung by measuring the transmission bremsstrahlung at the position of each detection element. It is believed that the object being measured may contain nuclides that emit gamma rays. These gamma rays are emitted at a constant emission rate regardless of time. On the other hand, pulsed bremsstrahlung generates very high intensity bremsstrahlung within the time range of the pulse, and does not generate any outside the time range of the pulse.

Therefore, by measuring the penetrating bremsstrahlung radiation only during the time range in which the pulsed bremsstrahlung radiation is generated, bremsstrahlung radiation of very high intensity is measured compared to gamma rays from nuclides that emit gamma rays, and the effect of gamma rays from nuclides that emit gamma rays on the penetrating bremsstrahlung radiation measurement can be kept very small.

The measurement object is placed on a measurement object rotation table and rotated to measure the intensity distribution of the transmitted bremsstrahlung from the measurement object from various directions. The density distribution of the measurement object is calculated from the intensity distribution data of the transmitted bremsstrahlung from all directions (360 degrees).

The pulsed fast neutrons irradiated to the object to be measured are also slowed down by a neutron reflector installed inside or outside the object to be measured. The slowed down pulsed fast neutrons undergo a nuclear reaction with the fissile material in the object to be measured, producing fast neutrons. These fast neutrons are measured by a neutron detector installed outside the object to be measured.

Since pulsed fast neutrons are generated corresponding to the irradiation time and irradiation time width of the pulsed fast electrons, the timing signal of the pulsed fast electrons is used to measure the peak value and measurement time of the measurement signal from the neutron detector based on the generation time of the pulsed fast neutrons. By collecting peak value data at each measurement time, the change over time in the peak value spectrum at the neutron detector is calculated.

If the number of peak value data at each measurement time is small, pulsed fast neutron irradiation may be repeated multiple times until a sufficient amount of peak value data is collected.

In the pulse-height spectrum of a neutron detector, below a certain value, noise signals that are not due to neutrons are included. In addition to electrical noise signals, noise signals also include noise signals due to gamma rays if the object being measured contains a nuclide that emits gamma rays. Like electrical noise signals, these noise signals due to gamma rays also have a lower pulse-height value compared to signals due to neutrons, so the change over time in the count rate of signals above the pulse-height value of a noise signal measured in advance is calculated.

Based on the change in this counting rate over time, the components of the neutrons are estimated: pulsed fast neutrons from the pulsed bremsstrahlung and pulsed fast neutron generating target, neutrons generated by the reaction of neutrons with fissile material in the object being measured, and neutrons generated from spontaneous fission nuclides contained in the object being measured. The amount of fissile material is calculated from the relationship between the amount of neutrons generated by the reaction of neutrons with fissile material measured in advance and the amount of fission nuclides.

The amount of fissile material derived from the density distribution within the measurement object is compared with the amount of fissile material derived from the neutron measurement results. If the two measurement results match within a certain range, the amount of fissile material derived from the density distribution within the measurement object, or the amount of fissile material derived from the neutron measurement results, is taken as the measurement result of the amount of fissile material contained in the measurement object. If the two measurement results differ outside a certain range, the measurement result with the greater amount of fissile material may be taken as the amount of fissile material contained in the measurement object.

The following describes the embodiments with reference to the drawings.

An example of a nuclear material measurement system according to the first embodiment will be described with reference to Figures 1 to 8.

Figure 1 shows an example of the configuration of the nuclear material measurement system of this embodiment.

The nuclear material measurement system shown in this figure comprises an electron beam accelerator 1, an electron beam accelerator control device 2, a signal converter 15, a transmission bremsstrahlung detector array 40, a neutron detector 50, and a data processing and analysis device 60.

The pulsed high-energy electron beam 10 emitted from the electron beam accelerator 1 is irradiated onto a target 20 for generating pulsed bremsstrahlung radiation and pulsed fast neutrons. This generates pulsed bremsstrahlung radiation 21 and pulsed fast neutrons 22, which are irradiated onto the measurement object 30. The bremsstrahlung radiation that has passed through the measurement object 30 and attenuated is measured by a transmission bremsstrahlung detector array 40. Meanwhile, the pulsed fast neutrons 22 irradiated onto the measurement object 30 are decelerated within the measurement object 30. The decelerated fast neutrons undergo a nuclear reaction with fissile material within the measurement object 30 to generate fast neutrons. These fast neutrons are measured by a neutron detector 50 installed outside the measurement object 30. Heavy metals such as gold and lead are used as the target 20.

The electron beam accelerator control device 2 issues a control signal 3 to the electron beam accelerator 1, and also issues a timing signal 4 to the signal converter 15. The electron beam accelerator 1 that receives the control signal 3 is configured to emit a pulsed high-energy electron beam 10. Furthermore, the signal converter 15 that receives the timing signal 4 is configured to issue a trigger and gate signal 5 to the data processing and analysis device 60. The data measured by the transmission bremsstrahlung detector array 40 and the neutron detector 50 is sent to the data processing and analysis device 60.

Figure 2 is a graph showing an example of the amount of bremsstrahlung radiation produced by electron beam irradiation.

When heavy metals such as gold and lead are irradiated with an electron beam, bremsstrahlung radiation is produced.

As shown in this figure, the maximum energy of the bremsstrahlung radiation generated is almost equal to the energy of the electron beam. The lower the energy of the bremsstrahlung radiation, the greater the amount produced.

Figure 3 is a graph showing an example of the reaction cross section of a reaction that produces one neutron by bremsstrahlung irradiation.

When heavy metals such as gold or lead are irradiated with bremsstrahlung radiation of a certain energy or more, a reaction occurs that produces neutrons, and neutrons are produced. Therefore, when heavy metals such as gold or lead are irradiated with an electron beam of energy above the reaction threshold for the reaction that produces neutrons by bremsstrahlung irradiation, bremsstrahlung radiation and neutrons are produced.

As shown in this figure, in the case of gold, the reaction threshold for producing one neutron by bremsstrahlung irradiation is approximately 8 MeV.

In the case of lead, the reaction threshold for generating one neutron by bremsstrahlung irradiation is approximately 7 MeV. Therefore, by irradiating heavy metals such as gold or lead with electrons of energy of approximately 7 to 8 MeV or more, it is possible to generate both bremsstrahlung and neutrons. Most of the neutron energy generated in this case is fast neutrons of 0.1 MeV or more. In addition, by pulsing the electron beam and irradiating heavy metals such as gold or lead with a pulsed high-energy electron beam 10, it is possible to generate both pulsed bremsstrahlung 21 and pulsed fast neutrons 22.

Figure 4 is a graph showing an example of the change over time in the intensity of a pulsed high-energy electron beam, the intensity of a pulsed bremsstrahlung radiation, and the intensity of a pulsed fast neutron.

Pulsed bremsstrahlung radiation and pulsed fast neutrons are generated according to the irradiation time and duration of the pulsed high-energy electron beam. In other words, the object to be measured is irradiated with pulsed bremsstrahlung radiation and pulsed fast neutrons emitted from the target by irradiation with the same pulsed high-energy electron beam. In the time range where the pulsed fast electron beam is not irradiated, neither pulsed bremsstrahlung radiation nor pulsed fast neutrons are generated.

In this diagram, the pulse width is about 1 μs to several μs. The time interval between pulses is about 2 to 10 ms.

In addition, in this diagram, the end times of each pulse of fast neutrons are used as the reference time.

It is believed that the object being measured may contain nuclides that emit gamma rays. These gamma rays are emitted at a constant emission rate regardless of time. On the other hand, pulsed bremsstrahlung generates very high intensity bremsstrahlung within the time range of the pulse, and is not generated outside the time range of the pulse. Therefore, by measuring penetrating bremsstrahlung only during the time range in which pulsed bremsstrahlung is generated, very high intensity bremsstrahlung is measured compared to gamma rays from nuclides that emit gamma rays, and the effect of gamma rays from nuclides that emit gamma rays on penetrating bremsstrahlung measurement can be kept very small.

Figure 5 is a block diagram showing the nuclear material measurement system of Figure 1.

Figure 5 shows the internal processing of the data processing and analysis device 60. That is, the data processing and analysis device 60 receives data from the transmission bremsstrahlung detector array 40 to calculate the density distribution of the measurement object, and receives data from the neutron detector 50 to measure the change in neutrons over time. This allows the amount of fissile material to be quantified.

In addition, in this figure, the measurement object 30 is configured to be rotatable.

By rotating the measurement object 30, the intensity distribution of the transmitted bremsstrahlung from the measurement object is measured from various directions. The data processing and analysis device 60 derives the density distribution of the measurement object from the intensity distribution data of the transmitted bremsstrahlung from all directions of 360 degrees.

The pulsed fast neutrons 22 irradiated to the object to be measured 30 are decelerated within the object to be measured 30. The decelerated pulsed fast neutrons undergo a nuclear reaction with the fissile material within the object to be measured, generating fast neutrons. These fast neutrons are measured by a neutron detector 50 installed outside the object to be measured. A neutron absorbing material such as cadmium is installed on the outside (surrounding) of the neutron detector 50, and the neutron absorbing material absorbs thermal neutrons, making it possible to measure only the fast neutrons. Cadmium, etc. are substances that are not thought to be mixed into the object to be measured.

Since pulsed fast neutrons corresponding to the irradiation time and irradiation time width of the pulsed fast electrons are generated, the timing signal of the pulsed fast electrons is used to measure the peak value and measurement time of the measurement signal from the neutron detector based on the generation time of the pulsed fast neutrons. By collecting peak value data at each measurement time, the change over time of the peak value spectrum in the neutron detector 50 is derived. If the number of peak value data at each measurement time is small, the pulsed fast neutrons may be irradiated multiple times until a sufficient amount of peak value data is collected.

Figures 6 and 7 are graphs showing examples of pulse-height spectrum of a neutron detector.

In the peak value spectrum of the neutron detector 50 (Figure 5), noise signals that are not due to neutrons are included below a certain value. In addition to electrical noise signals, noise signals also include noise signals due to gamma rays if the object being measured contains a nuclide that emits gamma rays. Like electrical noise signals, these noise signals due to gamma rays also have a lower peak value compared to signals due to neutrons, and so the change over time in the count rate of signals equal to or greater than the peak value of a noise signal measured in advance is derived. Noise signals due to bremsstrahlung are also included, but as the measurement of the change over time of fast neutrons is performed outside the time range in which bremsstrahlung is generated, there is no effect on the measurement of the change over time of fast neutrons.

Figure 8 is a graph showing an example of the change in fast neutron count rate over time in this embodiment.

Based on the change over time in the fast neutron count rate (solid line), the components of the pulsed fast neutrons (dashed line) from the pulsed bremsstrahlung and pulsed fast neutron generating target, the neutrons generated by the reaction of neutrons with fissile material in the measurement object (dash-dotted line), and the neutrons generated from spontaneous fission nuclides contained in the measurement object (dash-dotted line) are derived.

The amount of fissile material is derived from the relationship between the amount of neutrons produced by the reaction of previously measured fissile material with neutrons and the amount of fissile nuclides. The amount of fissile material derived from the density distribution in the measurement object is compared with the amount of fissile material derived from the neutron measurement results. If the two measurement results match within a certain range, the amount of fissile material derived from the density distribution in the measurement object or the amount of fissile material derived from the neutron measurement results is taken as the measurement result of the amount of fissile material contained in the measurement object. If the two measurement results differ outside a certain range, the measurement result with the greater amount of fissile material may be taken as the amount of fissile material contained in the measurement object.

Figure 9 is a perspective view showing the fissile material measurement system of Example 2.

In this diagram, a container 33 for the measurement object and a neutron detector 50 are installed on a rotating table 31 for the measurement object. The neutron detector 50 is arranged so as to surround the periphery of the container 33 for the measurement object. The container 33 for the measurement object is also simply called the "container."

By irradiating the target 20 with a pulsed high-energy electron beam 10, pulsed bremsstrahlung radiation 21 and pulsed fast neutrons 22 are generated. The bremsstrahlung radiation transmitted through the measurement object container 33 is detected by the transmitted bremsstrahlung detector array 40.

The transmitted bremsstrahlung detector array 40 has a configuration in which transmitted bremsstrahlung detectors 40a and transmitted bremsstrahlung detector shields 40b are alternately stacked and arranged in an array. The transmitted bremsstrahlung radiation is measured at the position of each transmitted bremsstrahlung detector 40a to measure the intensity distribution of the transmitted bremsstrahlung radiation. In this figure, the transmitted bremsstrahlung detectors are stacked in the height direction, so that the intensity distribution in the height direction can be accurately measured. Note that the arrangement of the transmitted bremsstrahlung detectors 40a and the transmitted bremsstrahlung detector shields 40b is not limited to that shown in this figure.

Figure 10 is a top view of the fissile material measurement system of Figure 9.

In Figure 10, the measurement object rotation table 31 in Figure 9 is omitted.

The measurement object (not shown) is placed inside the measurement object container 33. The measurement object container 33 is preferably a rotationally symmetric shape such as a cylindrical shape. The transmission bremsstrahlung detector array 40 is placed outside the measurement object container 33 in a position where the detector array is lined up in the height direction of the measurement object container 33. In addition, one or more neutron detectors 50 are placed outside the measurement object container 33 at a position that is not on a straight line connecting the target 20 and the transmission bremsstrahlung detector array 40. The multiple neutron detectors 50 may be placed in rotationally symmetric positions. The measurement object container 33 is placed on the measurement object rotation table 31. The measurement object container 33 rotates with the rotation of the measurement object rotation table 31, but the transmission bremsstrahlung detector array 40 and the neutron detector 50 do not rotate. The measurement object is irradiated with pulsed bremsstrahlung radiation 21 and pulsed fast neutrons 22, and after one pulse irradiation, the measurement object container 33 is rotated, stopped, and then one pulse irradiation is repeated, rotating 360 degrees to perform pulse irradiation.

Multiple pulses may be irradiated at one stationary position. Intensity distribution data of the transmitted bremsstrahlung after a 360-degree rotation is collected, and the density distribution of the object to be measured is derived based on the collected data. Measurements may also be performed while rotating the object rather than stationary. For fast neutrons, time-dependent change data of the fast neutron count rate after a 360-degree rotation is collected, and the collected data at each position is averaged, making it possible to derive the amount of fissile material in the object to be measured even if it is unevenly distributed.

Figure 11 is a perspective view showing the fissile material measurement system of the third embodiment.

In this figure, in addition to the configuration of Example 2, a neutron reflector 35 and a shielding body 41 for the transmission bremsstrahlung detector array are further installed.

The neutron reflector 35 is installed so as to surround the side of the measurement object container 33. The neutron reflector 35 has the role of reflecting neutrons and slowing down high-speed neutrons. A neutron detector 50 is installed between the measurement object container 33 and the neutron reflector 35. Two openings are provided in a part of the neutron reflector 35. One of them is located facing the opening, and a transmission bremsstrahlung detector array 40 is installed therein. The target 20 is installed inside the other one. The neutron reflector 35 contains graphite, iron, lead, etc.

Figure 12 is a perspective view showing the fissile material measurement system of Example 4.

In this figure, instead of the measurement object rotation table 31 (FIG. 9) of Example 2, a measurement object rotation and vertical movement table 32 is installed. In addition, the transmission bremsstrahlung detectors 40a and the transmission bremsstrahlung detector shields 40b that make up the transmission bremsstrahlung detector array 40 are stacked alternately in the horizontal direction.

The object to be measured (not shown) is placed inside the container 33 for the object to be measured. The container 33 for the object to be measured is placed on the platform 32 for rotating and vertically moving the object to be measured.

By irradiating the target 20 with the pulsed high-energy electron beam 10, pulsed bremsstrahlung radiation and pulsed fast neutrons are generated, and these are irradiated to the measurement object. In this case, after one pulse irradiation, the measurement object container 33 is rotated, stopped, and one pulse irradiation is repeated again, and pulse irradiation is performed by rotating 360 degrees. Multiple pulses may be irradiated at one stationary position. After collecting the intensity distribution data of the transmitted bremsstrahlung radiation after rotating 360 degrees, the measurement object container 33 is moved upward. After moving, the measurement object is irradiated with pulsed bremsstrahlung radiation 21 and pulsed fast neutrons 22, and after one pulse irradiation, the measurement object container 33 is rotated, stopped, and one pulse irradiation is repeated again, and pulse irradiation is performed by rotating 360 degrees. It is again moved upward, and by repeating this, the intensity distribution data of the transmitted bremsstrahlung radiation in all vertical directions is collected.

It is also possible to perform measurements while rotating and moving vertically at the same time, moving in a helical shape. In other words, measurements can be performed while moving in the rotational and vertical directions without stopping, and irradiating the measurement object with pulsed bremsstrahlung radiation and pulsed fast neutrons while moving.

The system disclosed herein can measure the change over time in the count rate of fast neutrons based on the time of generation of pulsed fast neutrons, and at the same time, the intensity distribution of bremsstrahlung radiation passing through the object being measured. This makes it possible to measure fissile materials in waste and stored materials from nuclear power plants, as well as in materials containing damaged or molten fuel, using multiple measurement methods, such as active neutron methods and X-ray CT, without changing the electron beam conditions, target, or measurement system.

1: Electron beam accelerator, 2: Electron beam accelerator control device, 3: Control signal, 4: Timing signal, 5: Trigger and gate signal, 10: Pulsed high energy electron beam, 15: Signal converter, 20: Target, 21: Pulsed bremsstrahlung, 22: Pulsed fast neutron, 30: Measurement object, 31: Measurement object rotation table, 32: Measurement object rotation and up/down movement table, 33: Measurement object container, 35: Neutron reflector, 40: Transmission bremsstrahlung detector array, 40a: Transmission bremsstrahlung detector, 40b: Transmission bremsstrahlung detector shield, 41: Transmission bremsstrahlung detector array shield, 50: Neutron detector, 60: Data processing and analysis device.

Claims (15)

An electron beam accelerator;
a target that receives the pulsed high-energy electron beam emitted from the electron beam accelerator and generates pulsed bremsstrahlung radiation and pulsed fast neutrons;
a transmission bremsstrahlung detector;
A neutron detector;
An electron beam accelerator control device,
the electron beam accelerator control device issues a control signal to the electron beam accelerator for controlling an irradiation time and an irradiation time width of the pulse high-energy electron beam;
a configuration in which the pulsed bremsstrahlung radiation and the pulsed fast neutrons emitted from the target by irradiation with the same pulsed high-energy electron beam are irradiated onto a measurement object,
the transmission bremsstrahlung detector measures the pulsed bremsstrahlung that has been transmitted through the measurement object within a time range of irradiation of the pulsed high-energy electron beam based on a timing signal generated by the electron beam accelerator control device together with the control signal ;
The neutron detector measures fast neutrons emitted from the object to be measured by irradiation with the pulsed fast neutrons outside the irradiation time range of the pulsed high-energy electron beam based on the timing signal emitted by the electron beam accelerator control device together with the control signal . A nuclear material measurement system. The nuclear material measurement system of claim 1, wherein the pulsed fast neutrons are generated by setting the energy of the pulsed high-energy electron beam to an energy equal to or greater than the reaction threshold of a reaction that produces neutrons by irradiating the target with the pulsed bremsstrahlung radiation. The nuclear material measurement system according to claim 1 or 2, wherein a neutron absorbing material is installed around the neutron detector. A neutron reflector is installed on the outside of the container of the measurement object,
The nuclear material measuring system according to any one of claims 1 to 3, wherein the neutron detector is installed between the container and the neutron reflector. The nuclear material measurement system according to claim 4, wherein the container of the measurement object is rotatably installed. The nuclear material measurement system according to claim 5, wherein the container of the measurement object is installed so as to be rotatable 360 degrees. The nuclear material measurement system according to claim 5 or 6, wherein the container for the measurement object is installed so as to be movable in the direction of its rotation axis. Further comprising a data processing and analysis device;
8. The nuclear material measurement system according to claim 1, wherein the data processing and analysis device calculates a density distribution of the measurement object from the measurement data of the transmission bremsstrahlung detector, and calculates an amount of fissile material contained in the measurement object from the density distribution. The nuclear material measurement system according to claim 8, wherein the data processing and analysis device identifies spontaneous fission nuclides contained in the measurement object from the measurement data of the neutron detector. an electron beam accelerator control device issuing a control signal to the electron beam accelerator for controlling an irradiation time and an irradiation time width of a pulse high-energy electron beam;
irradiating a target with the pulsed high-energy electron beam from the electron beam accelerator to generate pulsed bremsstrahlung radiation and pulsed fast neutrons, which are then irradiated onto a measurement object;
measuring the pulsed bremsstrahlung that has passed through the measurement object by a transmission bremsstrahlung detector within a time range of irradiation of the pulsed high-energy electron beam based on a timing signal generated by the electron beam accelerator control device together with the control signal ;
and measuring fast neutrons emitted from the object to be measured by the irradiation of the pulsed fast neutrons by a neutron detector outside the irradiation time range of the pulsed high-energy electron beam based on the timing signal generated by the electron beam accelerator control device together with the control signal ,
A method for measuring nuclear material, wherein the pulsed bremsstrahlung radiation and the pulsed fast neutrons are emitted from the target by irradiation with the same pulsed high-energy electron beam. The method for measuring nuclear material according to claim 10, further comprising a step of rotating the container of the object to be measured. The method for measuring nuclear material according to claim 11, wherein the container of the object to be measured is rotated 360 degrees. The method for measuring nuclear material according to claim 11 or 12, further comprising a step of moving the container of the object to be measured in the direction of its rotation axis. The method for measuring nuclear material according to any one of claims 10 to 13, further comprising the steps of calculating a density distribution of the measurement object from the measurement data of the transmission bremsstrahlung detector, and calculating the amount of fissile material contained in the measurement object from the density distribution. The method for measuring nuclear material according to any one of claims 10 to 14, wherein spontaneous fission nuclides contained in the measurement object are identified from the measurement data of the neutron detector.

Images