JP7307040B2 - Radioactivity concentration evaluation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating the radioactivity concentration of materials, equipment and waste generated at nuclear facilities.

Conventionally, it is necessary to check whether the radioactivity concentration of materials, equipment and waste generated at nuclear facilities (hereinafter collectively referred to as "radioactive waste") is below a predetermined value before being disposed of. be. Low-level radioactive waste whose radioactivity concentration is below a specified value is disposed of by a predetermined method. Regarding the disposal of radioactive waste, there is a system called a clearance system. In the clearance system, among radioactive wastes, the radioactivity concentration of radioactive materials is low and there is no need to consider the effect on human health. It is a system that can be disposed of or reused as general waste with the approval and confirmation of . In order to apply the clearance system to dispose of radioactive waste, it is necessary to confirm that the radioactivity concentration of the radioactive waste is below the clearance level at which it can be disposed and reused in the same way as general waste. be. The clearance level is the amount of radiation that is sufficiently small compared to the radiation level in the natural world and does not need to be treated as a radioactive substance for safety reasons. The clearance level is expressed in radioactivity concentration, that is, radioactivity per unit weight (becquerel/gram: Bq/g). , evaluate the radioactivity from the measured radiation and divide it by the measured weight to evaluate the radioactivity concentration (Bq/g).

When evaluating the radioactivity concentration of radioactive waste, there is a method of storing the radioactive waste in a container and measuring the radiation emitted from the radioactive waste outside the container. For example, as a prior art of this type, there is a method for measuring the density of a radioactive substance in which a gamma ray is irradiated from a radiation source for external irradiation to a container filled with an object to be measured containing a radioactive substance (see, for example, Patent Document 1). In this method, the first detection value obtained by measuring the sum of the gamma rays originating from the radiation source for external irradiation and the gamma rays originating from the object to be measured, and the second detection value obtained by measuring only the gamma rays emitted from the object to be measured , to measure the density of radioactive substances in the object to be measured.

Also, as another prior art, radioactive waste is placed in a container, the weight or density of the radioactive waste in the container is measured, and at least one of gamma rays and neutrons emitted from the radioactive waste in the container is measured. There is a radioactivity measuring device for radioactive waste that has been produced (see, for example, Patent Document 2).

JP-A-62-91879 JP-A-2003-75540

By the way, according to the government's review standards, in order to allow clearance of radioactive waste, the clearance specified for each nuclide, including the measured and evaluated radioactivity concentration (Bq/g) and the uncertainty of the result, is required. I am asking for a lower level. If the uncertainty of the measurement results is large, part of the volume assumed to be able to be cleared cannot be cleared and must be disposed of as low-level radioactive waste, resulting in an increase in management costs.

For this reason, when assessing the clearance level of radioactivity concentration of radioactive waste generated at nuclear facilities, the radioactive waste is stored uniformly in a container such as a predetermined iron box, or placed on a metal mesh tray at a height. While adhering to the restrictions, the uncertainty is kept small by arranging them so that they do not overlap, and the coefficient for converting the radiation count measured in the entire container to radioactivity is set on the safe side so that the radioactivity concentration can be greatly evaluated.

However, in order to store radioactive waste uniformly in a predetermined container such as an iron box, a lot of pretreatment work is required, such as cutting the radioactive waste into plates or finely, and this pretreatment work takes a lot of time. and labor.

Supposing, in order to reduce the time and labor required for pretreatment work, radioactive waste is randomly placed in the container (random means that pretreatment work that arranges radioactive waste uniformly) When stored, for example, when radioactive materials are unevenly attached to a part of the radioactive waste, the uncertainty of the measurement result becomes large.

Note that both Patent Documents 1 and 2 require time and labor to fill the container with radioactive waste because gamma rays are detected from the entire object to be measured filled in the container.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a radioactivity concentration evaluation method capable of measuring and evaluating the radioactivity concentration of radioactive waste randomly stored in a container.

In order to achieve the above object, a method for evaluating the concentration of radioactivity according to the present invention is a method for evaluating the concentration of radioactivity in radioactive waste. Divide into a plurality of regions, irradiate each divided region with radiation, measure the weight or density of the radioactive waste inside from the amount of radiation transmitted, and emit from the radioactive waste for each divided region The radiation is counted and the radiation-emitting nuclide is analyzed, and the radioactivity concentration of the target nuclide contained in the radioactive waste is evaluated from the radiation count value, the analysis result of the radiation-emitting nuclide, and the weight or density. "Radiation" in this specification and claims includes X-rays, synchrotron radiation, gamma rays, and the like.

With this configuration, the radioactive waste in the container is counted for weight or density and radiation and analyzed for radioactive nuclides for each of a plurality of divided areas, so even if the radioactive waste is randomly stored in the container, Radiation counts and radiation emitting nuclides can be adequately analyzed. Then, the radioactivity concentration of the target nuclide contained in the radioactive waste can be appropriately evaluated from the radiation count value, the analysis result of the radiation-emitting nuclide, and the weight or density. Therefore, it is possible to reduce the time and labor required for the work of storing the radioactive waste in the container, and improve the measurement accuracy in measuring the radioactive concentration.

In addition, the radiation emitted from the radioactive waste is counted by a radiation dosimeter , the radiation emitting nuclide emitted from the radioactive waste is analyzed by a radiation emitting nuclide analyzer , and the Based on the radionuclide analysis result of the radionuclide analyzer and the radionuclide analysis result, the radionuclide count is determined, and the radioactivity is evaluated by assigning the radiation count based on the radionuclide abundance ratio. good too.

With this configuration, the radionuclide abundance ratio is calculated based on the count for each radionuclide obtained from the detection of radiation by the radiation dosimeter and the analysis of the radiation-emitting nuclide by the radiation-emitting nuclide analyzer. radioactivity can be appropriately evaluated by assigning

Further, the evaluation of the radioactivity of the target nuclide contained in the radioactive waste based on the radiation count value and the analysis result of the radiation-emitting nuclide may be performed for each of the divided regions.

With this configuration, the radioactive waste in the container can be evaluated for the radiation count value and the radioactivity of the evaluation target nuclide for each divided area.

Further, the position, distribution and radioactivity of the radioactive substances adhering to the radioactive waste in the container may be estimated from the radiation count values measured for each of the divided areas.

With this configuration, the position, distribution, and radioactivity of the radioactive substances adhering to the radioactive waste in the container can be estimated from the radiation count value for each divided area.

Further, based on the weight measurement results for each divided area of the radioactive waste, the attenuation due to self-absorption of the radiation emitted from the radioactive waste is evaluated, and the attenuation is used to calculate the detection efficiency in counting the radiation. You may make it reflect.

With this configuration, the radiation attenuation due to the self-absorption of the radioactive waste can be reflected in the calculation of the radiation detection efficiency for each divided region.

In addition, the count value of the radiation, the detection value of the radiation-emitting nuclide analyzer, the position and distribution of the radioactive material adhering to the radioactive waste in the container, the estimation of the radioactivity, and the weight or The attenuation may be reflected in the calculation of the detection efficiency in counting the radiation from the density measurement result, and a radioactivity concentration conversion factor may be set for each of the divided regions.

With this configuration, the radiation count value, the detection value of the radionuclide analyzer, the position and distribution of the radioactive substances adhering to the radioactive waste, the estimation of the radioactivity, and the weight or density of each divided area. Based on the measurement results, it is possible to set a radioactivity concentration conversion factor that reflects radiation attenuation in the calculation of detection efficiency in radiation counting for each divided area.

In addition, combining the radiation count value counted by the radiation dosimeter , the radiation emitting nuclide analysis result analyzed by the radiation emitting nuclide analyzer, and the measurement result of the weight or density for each divided area, the radioactivity A concentration conversion factor may be used to evaluate the radioactivity concentration for each divided region.

With this configuration, the radioactivity concentration of each divided area is appropriately evaluated using the radioactivity concentration conversion factor from the radiation count value, the analysis result of the radiation-emitting nuclide, and the weight or density of each divided area. can do.

Further, the weight or density distribution of the radioactive waste in the container may be measured by reflecting the absorption of the radiation by the radioactive waste.

With this configuration, the absorption of radiation by the radioactive waste in the container can be reflected to appropriately evaluate the weight or density distribution of the radioactive waste.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the radioactivity concentration evaluation method which can measure and evaluate the radioactivity concentration of the radioactive waste accommodated in the container at random. Therefore, it is possible to greatly reduce the time and labor required to store radioactive waste in a container.

FIG. 1 is a perspective view schematically showing a state in which radioactive waste to be evaluated by a radioactive concentration evaluation method according to one embodiment of the present invention is stored in a container. FIG. 2 is a plan view showing an example of divided regions into which the container shown in FIG. 1 is virtually divided. FIG. 3 is a side view showing a radioactivity concentration evaluation device that implements a radioactivity concentration evaluation method according to one embodiment of the present invention. 4 is a plan view showing the radioactivity concentration evaluation apparatus shown in FIG. 3. FIG. FIG. 5 is a control block diagram in the radioactivity concentration evaluation device shown in FIG. 6 is a diagram showing data for evaluating the weight and density of radioactive waste from the amount of X-ray transmission in the weight distribution measurement unit shown in FIG. 3, (a) is an example graph showing concentration data, (b) is an example schematically showing the density of a transmission image. FIG. 7 is a perspective view schematically showing an arrangement example of the radiation dosimeter and the radiation-emitting nuclide analyzer shown in FIG. 8A to 8D are plan views showing an example of measuring the radiation dose for each divided region of the container shown in FIG. 2. FIG.

An embodiment of the present invention will be described below with reference to the drawings. In the following embodiments, the radioactivity concentration evaluation method will be described as an example of a radioactivity concentration evaluation device 1 that linearly feeds a container 10 (for example, an iron box) from one side to the other. Further, the container 10 of the following embodiment will be described as an example having a plurality of divided regions A to D obtained by virtually dividing the internal space into four in plan view. Also, an X-ray will be described as an example of radiation. The concept of vertical and horizontal directions in the documents of this specification and the scope of claims is consistent with the concept of vertical and horizontal directions in which the moving direction of the container 10 in the radioactivity concentration evaluation apparatus 1 shown in FIG. 1 is the horizontal direction. do.

(Container 10)
FIG. 1 is a perspective view schematically showing a state in which radioactive waste 100 to be evaluated by a radioactive concentration evaluation method according to one embodiment is stored in a container 10. FIG. FIG. 2 is a plan view showing an example of divided regions A to D into which the container 10 shown in FIG. 1 is virtually divided.

As shown in FIG. 1, the container 10 can be, for example, an iron box with dimensions of 100 cm to 150 cm in plan view and a height of about 50 cm. Radioactive wastes 100 are randomly placed in the body 11 of such a container 10 and closed with a lid 12 . When the radioactive waste 100 is randomly stored in the container 10, for example, it can be stored at a storage rate of about 25% to 30% of the total volume of the container 10. FIG.

As shown in FIG. 2, in this embodiment, the interior of the container 10 is virtually divided into four divided areas A to D in plan view. When the container 10 is viewed from above, the divided areas A to D are divided by imaginary lines 15 extending at 90° passing through the center point and divided in the circumferential direction. For example, when the vertical and horizontal dimensions of the container 10 are 100 cm, each of the divided regions A to D has a vertical and horizontal dimension of 50 cm in plan view. This division example is an example.

As will be described later, the weight distribution measuring unit 30 transmits X-rays from the outside to each of the divided regions A to D of the container 10, and the amount of transmitted X-rays obtained from each of the divided regions A to D is determined. The weight and density of the internal radioactive waste 100 at D are measured. A method for measuring the weight and density of the radioactive waste 100 from the amount of X-rays transmitted will be described later.

Measurement of the weight and density of the radioactive waste 100 by the weight distribution measurement unit 30 reveals the difference in packing density in each divided area A to D caused by the radioactive waste 100 being randomly stored inside the container 10. can be measured.

Further, for each of the divided areas A to D of the container 10, the radiation dose is measured by the plastic scintillator 55 of the radiation measurement unit 50, and the nuclide composition is measured by the Ge semiconductor detector 56, as will be described later. done. Then, from these measurement data, the radiation dose and nuclide composition of the radioactive waste 100 inside each divided area A to D are estimated. A method for estimating the radiation dose and nuclide composition of the radioactive waste 100 will be described later.

(Radioactive concentration evaluation device 1)
FIG. 3 is a side view showing the radioactivity concentration evaluation device 1 that implements the radioactivity concentration evaluation method according to one embodiment. FIG. 4 is a plan view showing the radioactivity concentration evaluation device 1 shown in FIG. In these figures, since the container 10 is sent from the left to the right, the left direction is also referred to as the upstream direction, and the right direction is also referred to as the downstream direction. Moreover, although these figures show an example in which a plurality of containers 10 flow simultaneously, the number of containers 10 flowing simultaneously in the radioactive concentration evaluation apparatus 1 is not limited to this example.

As illustrated, the radioactivity concentration evaluation apparatus 1 of this embodiment includes a weight measurement unit 20, a weight distribution measurement unit 30, a container rotation unit 40, and a radiation measurement unit 50. The container 10 is placed on the weight measurement unit 20 and sent to the weight distribution measurement unit 30 , the container rotation unit 40 and the radiation measurement unit 50 . In this embodiment, the internal space of the container 10 is virtually divided into four (FIG. 2), and weight distribution measurement and radiation measurement are performed for each of the divided regions AD. That is, as will be described later, the weight distribution measurement unit 30 and the radiation measurement unit 50 rotate the container 10 by 90° with the container rotation unit 40 in this embodiment so that each quarter of the container 10 is divided into four regions. Measurements are made for each of A to D. Therefore, since measurements are performed four times for each container 10, the container 10 is measured between the weight distribution measurement unit 30 and the container rotation unit 40, and between the radiation measurement unit 50 and the container rotation unit 40. In between, it is transported back and forth multiple times. The flow of rotating the container 10 by 90° is shown in FIG. 8, which will be described later.

Each operation of these weight measurement unit 20 , weight distribution measurement unit 30 , container rotation unit 40 and radiation measurement unit 50 is controlled by control device 60 .

Each unit 20, 30, 40, 50 will be described below.

[Weight measurement unit 20]
The weight measurement unit 20 is provided with a container transfer section 22 on the top of a pedestal 21 . The container conveying section 22 of this embodiment is a roller chain conveying section 23 in which a plurality of rollers are provided in the feeding direction. The container 10 is sent downstream (to the right) by the roller chain conveying section 23 . The roller chain conveying section 23 may or may not have a drive mechanism. In this embodiment, the weight measuring unit 20 also serves as a container receiving unit.

The weight measuring unit 20 of this embodiment is provided with a weight measuring instrument 25 for measuring the weight of the container 10 placed on the container transfer section 22 . The weight measuring instrument 25 is supported by a damper 26 provided on the pedestal 21 . The weight measuring instrument 25 can use, for example, a load cell system and can measure 1500 kgf to 2500 kgf as the maximum measuring capacity. The function of measuring the weight of the container 10 can also be provided in the container rotating unit 40 .

[Weight distribution measurement unit 30]
The weight distribution measuring unit 30 is provided with a container transfer section 32 on the top of the base 31 . This container conveying section 32 also serves as a roller chain conveying section 33 having a plurality of rollers provided in the feeding direction. The weight distribution measuring unit 30 of this embodiment reciprocates the container 10 so as to send the container 10 downstream to the container rotation unit 40 and back from the container rotation unit 40. It has become.

The weight distribution measuring unit 30 has a density measuring device for measuring the weight or density (hereinafter also referred to as “weight/density”) for each of the divided areas A to D obtained by virtually dividing the container 10 into four. ing. As a density measuring device, an X-ray measuring device is used in this embodiment. The X-ray irradiator 35 of the X-ray measuring device is arranged to irradiate X-rays from above the container 10 toward one of the divided regions AD. Below the container 10 at the position where the X-ray irradiation unit 35 is arranged, an X-ray detection unit 36 that obtains an image of the amount of transmission of the X-rays that have passed through the container 10 is provided. The weight and density of the radioactive waste 100 in the container 10 are measured (ascertained) by the controller 60 from the X-ray transmission amount obtained by the X-ray detector 36 . The details of the method for measuring the weight and density of the radioactive waste 100 will be described later.

As the X-ray irradiation unit 35, for example, one that can evaluate iron-based metals up to a maximum thickness of 100 mm can be used. The rated values of the tube voltage and tube current of the X-ray irradiation unit 35 may be set according to the thickness of the container 10, the material of the radioactive waste 100, and the like.

Since the weight distribution measuring unit 30 uses radiation (X-rays), it is covered with a shielding wall 37 that shields it from the outside.

[Container rotation unit 40]
The container rotating unit 40 is provided with a container transfer section 42 on the top of a base 41 . This container conveying section 42 also serves as a roller chain conveying section 43 having a plurality of rollers provided in the feeding direction. The container rotating unit 40 of this embodiment reciprocates the container 10 between the weight distribution measuring unit 30 and the radiation measuring unit 50 . Therefore, the roller chain conveying portion 43 can be driven in forward and reverse directions.

The container rotation unit 40 is provided with a disposition changing device 45 that lifts the container 10 from the roller chain conveying section 43 and rotates it. The arrangement changing device 45 has a contact portion 46 that contacts the lower surface of the container 10 and a jack portion 47 that raises and lowers the contact portion 46 . The jack portion 47 has a function of rotating the contact portion 46 by an angle of 90°. The jack portion 47 has a function of locking the position of the contact portion 46 each time it rotates. In this embodiment, in order to sequentially change the positions of the divided areas A to D obtained by dividing the container 10 into four in the circumferential direction, it is configured to be rotated by 90°, but the container 10 is divided into two divided areas. In such a case, it may be configured to be rotated by 180°. The arrangement changing device 45 may rotate the container 10 at an angle corresponding to the number of virtual divisions of the interior space of the container 10 .

[Radiation measurement unit 50]
The radiation measurement unit 50 is provided with a container transport section 52 on the top of a pedestal 51 . This container conveying portion 52 also serves as a roller chain conveying portion 53 having a plurality of rollers provided in the feeding direction. In the radiation measurement unit 50 as well, the roller chain conveying section 53 can be driven forward and backward so that the container 10 can be transported between the container rotating unit 40 and in the downstream direction.

The radiation measurement unit 50 includes a plastic scintillator 55 for measuring the radiation dose of the radioactive waste 100 in the container 10, and a composition for measuring the composition of radiation-emitting nuclides of the radioactive waste 100 (hereinafter simply referred to as "nuclide composition"). A Ge semiconductor detector 56 is provided. The plastic scintillator 55 is a radiation dosimetry device, and the Ge semiconductor detector 56 is a radiation emitting nuclide analyzer.

In this embodiment, the plastic scintillator 55 is designed to measure the radiation dose for each divided area A to D obtained by virtually dividing the container 10 into four. A pair of plastic scintillators 55 are provided above and below the container 10 . A known technique can be adopted for the plastic scintillator 55 .

In this embodiment, the Ge semiconductor detectors 56 are arranged so as to measure radiation-emitting nuclides in divided areas A to D different from the divided areas A to D in which the plastic scintillator 55 is arranged. In this embodiment, a Ge semiconductor detector 56 is arranged at the position of the divided area diagonal to the plastic scintillator 55 . The Ge semiconductor detector 56 can employ known technology. Thus, the plastic scintillator 55 and the Ge semiconductor detector 56 are designed to measure each divided area.

The radiation measurement unit 50 is covered with a shielding wall 57 that shields it from the outside so that radiation does not leak to the outside. A container delivery unit (not shown) may be provided downstream of the radiation measurement unit 50 .

(Control of radioactivity concentration evaluation device 1)
FIG. 5 is a control block diagram in the radioactivity concentration evaluation device 1 shown in FIG. In this figure, the control device 60 and the data processing section 61 are shown as separate blocks, but they can be integrated. The control device 60 (data processing unit 61) has a processor, a volatile memory, a nonvolatile memory, an I/O interface, and the like. The data processing unit 61 is implemented by a processor performing arithmetic processing using a volatile memory based on a program stored in a nonvolatile memory.

According to the radioactivity concentration evaluation apparatus 1, the following transmission/reception is performed between each unit 20, 30, 40, 50 and the control device 60 (including the data processing section 61). The configuration including the operation thereof will be described with reference to the configuration shown in FIGS.

The weight measurement unit 20 communicates with the control device 60 whether or not the container 10 has been placed at a fixed position. The position of the container 10 can be determined by detecting the position of the container 10 with a sensor. When the container 10 is placed in place, a signal from the controller 60 initiates weight measurement. After the weight measurement is completed, the container 10 is sent toward the weight distribution measuring unit 30 by the roller chain conveying section 23 . Weight measurement data in the weight measurement unit 20 is sent to the data processing section 61 and stored in a storage section (ROM, RAM, etc.). When the data is stored in the data processing section 61 , a signal is sent from the data processing section 61 to the control device 60 , and a signal is issued from the control device 60 to send the container 10 to the weight distribution measuring unit 30 .

The weight distribution measuring unit 30 transmits/receives with the controller 60 whether or not the container 10 is placed at a fixed position. The position of the container 10 can be determined by detecting the position of the container 10 with a sensor. When the container 10 is placed at a fixed position, the measurement planes (virtually divided planes) of the divided areas A to D placed at the position of the X-ray irradiation unit 35 are recognized. In this example, the divided areas A are recognized in order. When the divided area A is recognized, a signal from the control device 60 starts measurement. As a result, the divided region A is irradiated with X-rays from the X-ray irradiation unit 35, and the X-ray detection unit 36 obtains the amount of transmission. The transmission amount obtained by the X-ray detector 36 is sent to the data processor 61 . When data is stored in data processing unit 61 , a signal is sent from data processing unit 61 to control device 60 . When the measurement of the divided area A of the container 10 is completed by the weight distribution measuring unit 30 in this way, the control device 60 issues a normal rotation instruction to the roller chain conveying section 33 , and the container 10 is sent to the container rotating unit 40 . .

In the container rotation unit 40, when the container 10 is sent to a fixed position, the control device 60 issues an instruction to rotate the container 10 by 90°. When the container rotating unit 40 rotates the container 10 by 90°, the control device 60 issues a reversing instruction to the roller chain conveying unit 43, and the container 10 is returned to the weight distribution measuring unit 30 in the upstream direction. The container 10 returned to the weight distribution measuring unit 30 recognizes that the divided area B is placed at the position of the X-ray irradiation unit 35 , and the divided area B is irradiated with X-rays from the X-ray irradiation unit 35 . Then, the transmission amount obtained by the X-ray detection unit 36 is sent to the data processing unit 61 .

When the measurement of the divided area B of the container 10 is completed by the weight distribution measuring unit 30 in this manner, the control device 60 issues a normal rotation instruction to the roller chain conveying section 33, and the container 10 is sent to the container rotating unit 40. . After that, after the container 10 is rotated by 90° by the container rotation unit 40, the weight and density are measured by the weight distribution measurement unit 30 for the divided area C and the divided area D in the same manner as the measurement for the divided area B. will be The measurement of the weight and density in each of the divided regions A to D is the same as that shown in FIGS.

When the weight and density measurements for all the divided regions A to D are completed, the roller chain conveying section 33 is driven to rotate forward by a signal from the control device, and the container 10 is sent to the container rotating unit 40 . In this embodiment, the container 10 sent to the container rotation unit 40 is rotated by 90° so that the divided area A is returned to the initial position, and then sent downstream from the container rotation unit 40 to the radiation measurement unit 50 . Sent.

For the container 10 sent to the radiation measurement unit 50 , transmission/reception is performed between the control device 60 and whether or not the container 10 has been placed at the fixed position. The position of the container 10 can be determined by detecting the position of the container 10 with a sensor. When the container 10 is placed at a fixed position, it is recognized that the divided areas A, which are virtually divided into four, are placed at the positions of the plastic scintillators 55 . When the divided area A is recognized, the plastic scintillator 55 starts measuring the radiation dose in the divided area A. FIG. Also, in this state, the segmented region C is located at the position of the Ge semiconductor detector 56 , and the radiation emitting nuclide in the segmented region C is detected by the Ge semiconductor detector 56 . The measured value of the radiation dose measured in the divided area A and the detected value of the radiation emitting nuclide detected in the divided area C are sent to the data processing unit 61 and recorded.

Then, in this embodiment, when the measurement of the radiation dose in the divided area A and the detection of the radiation-emitting nuclide in the divided area C are completed, the control device 60 issues a reversing instruction to the roller chain conveying section 53, and the container 10 is turned into a container. It is sent to the rotating unit 40 . The container 10 sent to the container rotation unit 40 is rotated by 90° by the repositioning device 45 . When the container 10 is rotated by 90° by the container rotation unit 40 , the control device 60 issues a normal rotation instruction to the roller chain conveying section 43 , and the container 10 is sent to the radiation measurement unit 50 .

After that, when it is recognized that the divided area B of the container 10 is positioned at the position of the plastic scintillator 55, the plastic scintillator 55 starts measuring the radiation dose in the divided area B. FIG. Further, in this state, the divided area D is arranged at the position of the Ge semiconductor detector 56, and the Ge semiconductor detector 56 also detects radiation-emitting nuclides in the divided area D. FIG. The measured value of the radiation dose measured in the divided area B and the detected value of the radiation emitting nuclide detected in the divided area D are sent to the data processing unit 61 and recorded.

Then, when the measurement of the radiation dose in the divided area B and the detection of the nuclide composition in the divided area D are completed, the container 10 is sent to the container rotation unit 40 by a signal from the control device 60, and the container rotation unit 40 It is rotated 90° by the repositioning device 45 . The container 10 rotated by 90° by the container rotation unit 40 is sent to the radiation measurement unit 50, and the measurement of the radiation dose in the next divided area C and the detection of the radiation emitting nuclide in the divided area A are performed in the same way. done. After that, the radiation dose for the divided area D and the radiation emitting nuclide detection for the divided area B are performed in the same manner.

According to this radioactivity concentration evaluation apparatus 1, in order to evaluate the radioactivity of the radioactive waste 100, measurement is performed by the Ge semiconductor detector 56, which is a radiation emission nuclide analyzer capable of measuring the energy spectrum of gamma rays for each divided area. By adding, it is possible to obtain the abundance ratio of nuclides to be measured/evaluated, and distribute the count values obtained by all gamma-ray measurements to each nuclides.

(Evaluation of weight distribution by weight distribution measurement unit 30)
FIG. 6 is a diagram showing data for evaluating the weight and density of the radioactive waste 100 from the X-ray transmission amount in the weight distribution measurement unit 30 shown in FIG. and (b) is an example schematically showing the density (gray scale) of a transmission image. FIG. 6(a) shows changes in the plate thickness of the radioactive waste 100 and changes in gray scale density.

In the weight distribution measuring unit 30, the X-ray irradiation unit 35 irradiates the container 10 with X-rays, and the X-ray transmission amount obtained by the X-ray detection unit 36 is used to determine the weight of the radioactive waste 100 in the container 10.・The density distribution is measured (understood). In FIG. 6, the tube voltage when X-rays are irradiated from the X-ray irradiation unit 35 and the density of the gray scale generated by the amount of transmission that changes according to the density (thickness) of the radioactive waste 100 stored in the container 10. showing relationships.

That is, X-rays are irradiated from the X-ray irradiation unit 35 at a predetermined tube voltage, and the relationship between the plate thickness of the radioactive waste 100 at that time and the amount of transmission (which can be expressed by the density change of the transmission image) is tested in advance. , and based on these relationships, create a map of plate thickness in relation to the amount of X-ray transmission. It can be seen from the graph in (a) that the transmission image that changes depending on the amount of X-ray transmission has a light density when the plate thickness of the radioactive waste 100 is thin, and a high density when the plate thickness is thick. That is, as schematically shown in (b), the transmission image when the plate thickness is thin is light as shown on the left side of the figure, and the transmission image when the plate thickness is thick is shown on the right side of the figure. darkens to The illustrated graph shows an example of measuring the radioactive waste 100 of ferrous metal at a tube voltage of 220 kV. Maps created from such relationships are created by conducting accurate tests on multiple maps when the tube voltage is changed and a specific plate thickness range (for example, 30mm-50mm, 50mm-100mm). You can also For example, based on the relationship between these test results, a map can be created as an output as an evaluation of the metal thickness distribution (=weight density distribution) using the data of the tube voltage and the amount of X-ray transmission as the input side.

Then, based on these test results, a calculation system (program) capable of conversion to weight density distribution can be created based on a map created from the tube voltage and the amount of transmission when irradiated with X-rays. This calculation system converts the data obtained from the amount of transmitted X-rays detected by the X-ray detection unit 36 of the weight distribution measurement unit 30 into a weight density distribution, and measures (understands) the weight and density. can be done.

In addition, a measuring device including this calculation system measures (estimates) the weight distribution for each of the divided areas A to D from the X-rays irradiated from the X-ray irradiation unit 35 and the absorption of the X-rays by the radioactive waste 100. It may be provided with functions. That is, based on the weight measurement results for each of the divided areas A to D of the radioactive waste 100, the attenuation due to self-absorption of the radiation emitted from the radioactive waste 100 is evaluated, and this attenuation is used to calculate the detection efficiency in radiation counting. may be reflected in

Based on the total weight of the container 10 previously measured by the weight measurement unit 20, the weight/density data obtained by the weight distribution measurement unit 30 may be assigned to the weights of the divided regions A to D. . In addition, since the transmission dose becomes saturated or unmeasurable at a certain dose due to the difference in packing density of the radioactive waste 100, the appropriate transmission dose is obtained by changing several patterns of the tube voltage for each of the divided areas A to D. You may make it calculate an exact weight and density by this.

Also, the method of estimating the weight and density of the radioactive waste 100 based on the amount of X-ray transmission is not limited to this embodiment. For example, the relationship shown in FIG. 6 may be obtained, and the following formula may be derived from this relationship.
G=f(V)×g(d)
However, G is a gray scale, f(V) is a function of tube voltage, and g(d) is a function of density.

According to the weight distribution measuring unit 30, the amount of X-ray transmission obtained by irradiating X-rays to each of the four divided areas A to D obtained by virtually dividing the container 10 into four divided areas is measured. The weight and density inside A to D can be grasped. Therefore, if the radioactive waste 100 is not pretreated and is randomly stored in the container 10, a difference in packing density occurs in each divided area A to D of the container 10. By weight distribution measurement based on the amount of transmission obtained by the X-ray detection unit 36 by irradiating with , the weight and density in the four divided areas A to D can be properly grasped.

(Measurement by radiation measurement unit 50)
FIG. 7 is a perspective view schematically showing an arrangement example of the radiation dosimetry device (plastic scintillator 55) and the radiation emission nuclide analyzer (Ge semiconductor detector 56) shown in FIG. 8A to 8D are plan views showing an example of measuring the radiation dose for each of the divided regions A to D of the container 10 shown in FIG. 2. FIG.

As shown in FIG. 7, the radiation measurement unit 50 in this embodiment measures the radiation dose (counts the radiation) with a plastic scintillator 55 for one of the divided areas A to D of the container 10, and measures the divided areas A to D. A Ge semiconductor detector 56 for the other one of D detects radiation-emitting nuclides. Thereby, the radiation dose measurement by the plastic scintillator 55 and the radiation emission nuclide measurement by the Ge semiconductor detector 56 can be efficiently performed.

Measurement of radiation dose and radiation emission nuclide measurement by the radiation measurement unit 50 will be described below with reference to FIGS. 8(a) to 8(d).

As shown in FIG. 8( a ), for the container 10 placed at a predetermined position of the radiation measurement unit 50 , in the divided area A, the radiation dose in the divided area A is measured by the plastic scintillator 55 arranged in the vertical direction of the container 10 . is measured. Further, in the divided area C, detection of the radiation-emitting nuclide in the divided area C is performed by the Ge semiconductor detector 56 arranged above the container 10 . After measuring the radiation dose in the divided area A and detecting the radiation-emitting nuclide in the divided area C, the container 10 is sent to the container rotation unit 40, rotated by 90°, and then returned to the radiation measurement unit 50. be

Next, as shown in FIG. 8B, in the divided area B, the radiation dose in the divided area B is measured by the plastic scintillator 55 arranged in the vertical direction of the container 10 . Further, in the divided area D, detection of the radiation-emitting nuclide in the divided area D is performed by the Ge semiconductor detector 56 arranged above the container 10 . After measuring the radiation dose in the divided area B and detecting the radiation emitting nuclide in the divided area D, the container 10 is sent to the container rotation unit 40, rotated by 90°, and then returned to the radiation measurement unit 50. be

In this embodiment, since the container 10 is virtually divided into four divided areas A to D, next, as shown in FIG. Detection of radiation-emitting nuclides at A is performed. After that, it is rotated by 90° as described above, and then, as shown in FIG.

In this way, the measurement of the radiation dose and the detection of the radiation-emitting nuclide are performed for all of the divided areas A to D.

(Example of evaluation method)
[Creation of radioactivity concentration conversion factor]
Create a radioactivity concentration conversion factor for evaluating (estimating) the radioactivity concentration (Bq/g) of the radioactive waste 100 from the radiation dose measurement results (cps) for each of the divided areas A to D. . The radioactivity concentration conversion factor is set based on detailed evaluation based on theoretical calculations such as QAD (point attenuation nuclear integration method analysis code) for a model assuming the actual scale of a simulated test.

The radioactivity concentration conversion factor is obtained as a function of the penetration thickness estimated based on the count value of the radiation dose measured for each divided area A to D and the measurement results of the weight and density as the main parameters. The radioactivity concentration conversion coefficient reflects the estimation of the position, distribution and radioactivity of the radioactive substances attached to the radioactive waste 100 and the attenuation due to self-absorption in the calculation of the detection efficiency in counting radiation, and is calculated for each divided area A to D can be asked for. It is desirable that this radioactivity concentration conversion factor eliminate excessive conservativeness as much as possible while sufficiently reducing the probability that the evaluation result will be lower than the actual radioactivity concentration.

As the radiation dose count value (absolute value), the value of the plastic scintillator 55 is used, and the radioactivity concentration inside each of the divided regions A to D can be evaluated by the radioactivity concentration conversion factor incorporated in the evaluation system.

The appropriateness of the radioactivity concentration conversion factor that has been set can be confirmed through simulation tests such as mock tests and MCNP (Monte Carlo N-Particle Transport Code).

In addition, the radiation count value obtained by the plastic scintillator 55 and the radiation emission nuclide analysis result of the Ge semiconductor detector 56 are obtained, and the radiation count value is assigned based on the abundance ratio of the radionuclide. can also be used to assess radioactivity concentration.

[Create evaluation model formula]
By detailed evaluation such as MCNP, it is possible to create an evaluation model formula with conservativeness within a reasonable range and a safety factor for the clearance criterion value. A reasonable range means a range that eliminates excessive conservativeness while ensuring that the probability that the evaluation result is lower than the actual radioactivity concentration is sufficiently low.

The evaluation model formula is incorporated in the control device 60 as a formula that inputs the input values (cps, g/cm ² at the measurement position) from the radiation emitting nuclide analyzer (Ge semiconductor detector 56).

The radioactivity concentration level of the radioactive waste 100 is expected to be about 1/10 of the clearance criterion value (clearance level), and as the detection limit concentration upper limit, for example, Co- For 60, it can be 0.01 Bq/g, which is 1/10 of the clearance level.

[Evaluation of radioactivity concentration]
According to the above-described radioactivity concentration evaluation apparatus 1, for each of the divided regions A to D obtained by virtually dividing the internal space of the container 10 into four in plan view, the radioactive It becomes possible to appropriately evaluate the radioactivity concentration of the target nuclide contained in the waste. According to the radioactive concentration evaluation device 1, even if the radioactive waste 100 is randomly stored in the container 10, the radioactive concentration of the radioactive waste 100 is accurately measured for each of the plurality of divided areas A to D. can do. Therefore, by storing the radioactive waste 100 in the container 10 at random, it is possible to greatly reduce the time and labor required to store the radioactive waste 100 in the container 10 .

The radioactivity concentration can also be evaluated by allocating radiation count values based on the abundance ratio of radionuclides. Furthermore, the radioactivity concentration of the target nuclide contained in the radioactive waste 100 can be evaluated for each of the divided areas A to D.

Then, by appropriately evaluating the radioactivity concentration of the radioactive waste 100, if the radioactivity concentration of the radioactive waste 100 in all the divided areas A to D is below the clearance level, the radioactivity in the container 10 The waste 100 can be disposed of and reused in the same manner as general waste. Therefore, it is possible to reduce the management cost.

Also, when the radioactivity concentration exceeds the clearance level in a part of the divided areas A to D, the radioactive waste 100 in the divided areas A to D exceeding the clearance level is individually disposed of as low-level radioactive waste 100. Alternatively, based on the evaluation of the entire radioactive waste 100 in the container 10, appropriate disposal can be taken.

(Other modifications)
In the radioactivity concentration evaluation method of the embodiment described above, an example in which the internal space of the container 10 is virtually divided into four in plan view has been described, but the number of virtual divisions of the internal space of the container 10 is four. Not limited. The number of virtual divisions of the internal space of the container 10 may be set according to the size of the container 10, the size that can be measured by a density measuring device, and the like.

Further, although the radioactivity concentration evaluation apparatus 1 of the above-described embodiment is an example in which the units 20, 30, 40, and 50 are linearly arranged, the units 20, 30, 40, and 50 are linearly arranged. not limited to this embodiment. For example, the weight distribution measurement unit 30 and the radiation measurement unit 50 can be arranged side by side, and the container rotation unit 40 can be arranged between them.

Moreover, the combination of each configuration in the above-described embodiment is an example, and a part of the configuration may serve as two configurations. For example, the container rotation unit 40 may be provided with the function of the weight measurement unit 20, and these units may be configured as one unit. Moreover, although the radioactivity concentration evaluation apparatus 1 of this embodiment has been described as having the weight measurement unit 20 , the weight measurement of the container 10 can also be performed outside the radioactivity concentration evaluation apparatus 1 . For example, weight measurements can be made using known load cell weigh scales. Thus, the combination of each configuration is not limited to the above-described embodiments.

Moreover, the above-described embodiment shows an example, and various modifications are possible without departing from the gist of the present invention. For example, a configuration in which a container receiving unit (not shown) is provided upstream of the weight distribution measuring unit 30 and a container discharge unit (not shown) is provided downstream of the radiation measuring unit 50 may be employed. is not limited to

(Summary)
According to the radioactivity concentration evaluation method described above, by measuring the weight or density distribution for each divided area A to D obtained by virtually dividing the internal space of the container 10, the radioactive materials randomly stored in the container 10 It becomes possible to appropriately grasp the weight and density of the waste 100 and appropriately evaluate the radioactivity concentration. In other words, it is expressed in terms of radioactivity per unit weight (becquerel/gram: Bq/g), and is emitted from radiation measured using a clearance measurement device approved by the government as a method for measuring and evaluating radioactivity concentration. It is possible to estimate the radioactivity concentration (Bq/g) by estimating the activity and dividing by the measured weight.
Therefore, by randomly storing the radioactive waste 100 in the container 10, pretreatment work such as cutting the radioactive waste 100 and evenly spreading it can be greatly reduced, and the work of storing the radioactive waste 100 in the container 10 can be greatly reduced. It is possible to greatly reduce the time and labor required for

Then, from the radiation dose and nuclide composition in each divided area A to D measured by the radiation measurement unit 50, the radioactivity concentration (Bq/g) of the radioactive waste 100 randomly stored inside the container 10 is determined by the clearance It is possible to appropriately evaluate whether or not the level exceeds a predetermined set value (for example, about 1/10 of the clearance level). As a result of this evaluation, if the radioactive waste 100 is below the clearance level that does not need to be treated as a radioactive material for safety, it can be properly disposed of as general waste, making it possible to reduce management costs. .

1 Radioactivity Concentration Evaluation Device 10 Container 15 Virtual Line 20 Weight Measuring Unit 25 Weight Measuring Instrument 30 Weight Distribution Measuring Unit 35 X-Ray Irradiator (Density Measuring Instrument)
36 X-ray detector (density measuring instrument)
37 Shielding Wall 40 Container Rotating Unit 45 Layout Changing Device 50 Radiation Measuring Unit 55 Plastic Scintillator (Radiation Dosimeter)
56 Ge semiconductor detector (radiation emission nuclide analyzer)
57 shielding wall 60 control device 61 data processing unit 100 radioactive waste A to D divided areas

Claims (8)

A radioactive concentration evaluation method for radioactive waste,
Putting the radioactive waste in a container,
Virtually dividing the internal space of the container into a plurality of divided regions,
irradiating each divided region with radiation, measuring the density of the radioactive waste inside from the amount of radiation transmitted;
Counting the radiation emitted from the radioactive waste for each of the divided areas with a radiation dosimeter and analyzing radiation emitting nuclides with a radiation emitting nuclide analyzer,
Evaluating the radioactivity concentration of the nuclide to be evaluated contained in the radioactive waste from the count value of the radiation, the analysis result of the radiation-emitting nuclide, and the density;
A radioactive concentration evaluation method characterized by: counting the radiation emitted from the radioactive waste by a radiation dosimeter ;
Analyzing radiation-emitting nuclides emitted from the radioactive waste with a radiation-emitting nuclide analyzer,
Calculate the count for each radionuclide from the radiation count value obtained by the radiation dosimeter and the radiation emission nuclide analysis result of the radiation emission nuclide analyzer, and assign the radiation count value based on the radionuclide abundance ratio assess radioactivity,
The radioactive concentration evaluation method according to claim 1. Evaluation of the radioactivity of the target nuclide contained in the radioactive waste based on the radiation count value and the analysis result of the radiation-emitting nuclide is performed for each of the divided areas,
The radioactive concentration evaluation method according to claim 2. estimating the position, distribution and radioactivity of the radioactive materials adhering to the radioactive waste in the container from the radiation count values measured for each of the divided areas;
The radioactive concentration evaluation method according to claim 2 or 3. Based on the density measurement results for each divided area of the radioactive waste, the attenuation due to self-absorption of the radiation emitted from the radioactive waste is evaluated, and the attenuation is reflected in the calculation of the detection efficiency in counting the radiation. I made it
The radioactive concentration evaluation method according to claim 4. The count value of the radiation, the detection value of the radiation-emitting nuclide analyzer, the position, distribution, and radioactivity estimation of the radioactive material adhering to the radioactive waste in the container, and the measurement result of the density for each of the divided regions From, the attenuation is reflected in the calculation of the detection efficiency in counting the radiation, and a radioactivity concentration conversion factor is set for each divided area,
The radioactive concentration evaluation method according to claim 5. Combining the radiation count value counted by the radiation dosimeter , the radiation emitting nuclide analysis result analyzed by the radiation emitting nuclide analyzer, and the density measurement result for each divided area,
evaluating the radioactivity concentration for each of the divided regions by the radioactivity concentration conversion factor;
The radioactive concentration evaluation method according to claim 6. The measurement of the density distribution of the radioactive waste in the container reflects the absorption of the radiation by the radioactive waste,
The radioactive concentration evaluation method according to any one of claims 1 to 7.

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