JP7112989B2 - Radioactivity evaluation method, radioactivity measurement method and radioactivity measurement device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radioactivity evaluation method, a radioactivity measurement method, and a radioactivity measurement device.

For example, Patent Literature 1 and Patent Literature 2 disclose techniques for measuring the amount of radioactivity in radioactive waste stored in a storage container. Patent Literature 1 aims to evaluate radioactivity concentration with high accuracy even when radioactive waste stored in a rectangular storage container has a density distribution or uneven distribution. Further, Patent Document 2 aims at accurately measuring the amount of radioactivity in radioactive waste stored in a rectangular storage container.

JP 2018-072017 A JP 2014-115272 A

However, in Patent Document 1, in order to evaluate the radioactivity concentration with high accuracy even when there is a density distribution or uneven distribution, it is necessary to register the storage pattern. There is a problem that highly accurate evaluation cannot be performed in the storage container. In addition, in Patent Document 2, by performing a correction using the shape of the spectrum when calculating the amount of radioactivity, it is shown that the effects of uneven distribution of density and uneven distribution of radiation sources in the measurement target are alleviated. It is desired to evaluate the amount of radioactivity in consideration of the uneven distribution of radiation sources. In addition, in devices for measuring radioactivity, miniaturization and shortening of operating time are desired.

The present invention solves the above-mentioned problems, and is a radioactivity evaluation method that can easily evaluate the amount of radioactivity in radioactive waste stored in a rectangular storage container while considering uneven distribution of density and uneven distribution of radiation sources. intended to provide In addition, the present invention is intended to solve the above-mentioned problems, and is a radioactivity measuring device capable of shortening the operation time and miniaturizing the device for measuring the radioactivity amount of radioactive waste stored in a rectangular storage container. An object of the present invention is to provide a measuring method and a radioactivity measuring device.

To achieve the above object, a radioactivity evaluation method according to one aspect of the present invention is a radioactivity evaluation method for evaluating the radioactivity of radioactive waste stored in a rectangular storage container, wherein radiation is detected a step of obtaining a first safety factor based on uneven distribution of internal contamination; a step of obtaining a second safety factor based on uneven distribution of radiation sources; and determining the amount of radioactivity of the radiation.

In order to achieve the above object, a radioactivity measuring method according to one aspect of the present invention is a radioactivity measuring method for measuring radiation of radioactive waste stored in a rectangular storage container, A measurement unit integrally provided with a smear measurement unit for measuring surface contamination of the container and a radiation measurement unit for measuring the radiation of the radioactive waste is moved along the outer surface of the rectangular storage container to measure the radiation. Including process.

In order to achieve the above object, a radioactivity measuring device according to one aspect of the present invention is a radioactivity measuring device for measuring radiation of radioactive waste stored in a rectangular storage container, A measurement unit integrally provided with a smear measurement unit for measuring surface contamination of the container and a radiation measurement unit for measuring the radiation of the radioactive waste, and the measurement unit is moved along the outer surface of the square storage container. and a moving part.

According to the radioactivity evaluation method of the present invention, the amount of radioactivity in radioactive waste stored in a rectangular storage container can be easily evaluated while considering uneven distribution of density and uneven distribution of radiation sources. Moreover, according to the radioactivity measuring method and the radioactivity measuring apparatus of the present invention, it is possible to shorten the operation time for measuring the amount of radioactivity in the radioactive waste stored in the rectangular storage container and to reduce the size of the apparatus.

FIG. 1 is a schematic plan view of the first unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 2 is a schematic side view of the first unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 3 is a schematic front view of the first unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 4 is a schematic diagram of the measuring section of the radioactivity measuring device according to the embodiment of the present invention. FIG. 5 is a schematic plan view of the second unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 6 is a schematic side view of the first unit of the radioactivity measuring device according to the embodiment of the present invention. FIG. 7 is a flow chart showing the operation of the radioactivity measuring device according to the embodiment of the present invention. FIG. 8 is a flow chart showing a radioactivity evaluation method according to an embodiment of the present invention. FIG. 9 is a graph showing an example of radiation measurement results. FIG. 10 is a graph showing an example of a correction curve for radiation source uneven distribution in the radioactivity evaluation method according to the embodiment of the present invention. FIG. 11 is a flow chart showing setting of the first safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 12 is a model diagram of a rectangular storage container in setting the first safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 13 is a model diagram of the first radiation transmittance in setting the first safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 14 is a model diagram of the second radiation transmittance in setting the first safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 15 is a graph showing an example of radiation source uneven distribution in setting the second safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 16 is a graph showing an example of analysis results in setting the second safety factor of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 17 is a flow chart showing the radioactivity evaluation method when the radioactivity evaluation method according to the embodiment of the present invention is below the detection limit. FIG. 18 is a model diagram of a rectangular storage container in the case of below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 19 is a model diagram of an example of a radiation source assumed in the case of below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 20 is a model diagram of an example of a radiation source assumed in the case of below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 21 is a model diagram of an example of a radiation source assumed in the case of below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 22 is a model diagram of an example of a radiation source assumed to be below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 23 is a table comparing the uniform radiation source model and the plane radiation source model in the case of below the detection limit of the radioactivity evaluation method according to the embodiment of the present invention. FIG. 24 is a graph of an example of an approximation curve for setting a conversion factor when the radioactivity evaluation method according to the embodiment of the present invention is below the detection limit.

EMBODIMENT OF THE INVENTION Below, embodiment which concerns on this invention is described in detail based on drawing. In addition, this invention is not limited by this embodiment. In addition, components in the following embodiments include components that can be easily replaced by those skilled in the art, or components that are substantially the same.

[Radioactivity measuring device and radioactivity measuring method]
FIG. 1 is a schematic plan view of the first unit of the radioactivity measuring device according to this embodiment. FIG. 2 is a schematic side view of the first unit of the radioactivity measuring device according to this embodiment. FIG. 3 is a schematic front view of the first unit of the radioactivity measuring device according to this embodiment. FIG. 4 is a schematic diagram of the measuring section of the radioactivity measuring apparatus according to this embodiment. FIG. 5 is a schematic plan view of the second unit of the radioactivity measuring device according to this embodiment. FIG. 6 is a schematic side view of the first unit of the radioactivity measuring device according to this embodiment.

The radioactivity measuring apparatus of this embodiment measures the radioactivity of radioactive waste stored in a rectangular storage container 100 indicated by a dashed line in FIGS. 1 to 6. FIG. The square storage container 100 is a rectangular parallelepiped, for example, a cube with a side of 1.6 m and a thickness of 0.05 m. The rectangular container 100 contains radioactive waste and is filled with mortar. Compared with a cylindrical drum-shaped storage container, the rectangular storage container 100 can be placed without gaps, and efficiency in transportation and arrangement can be achieved.

The radioactivity measuring device of this embodiment includes a first measurement unit 11 shown in FIGS. 1 to 3 and a second measurement unit 21 shown in FIGS. Moreover, the first measurement unit 11 and the second measurement unit 21 are provided with the measurement part 31 shown in FIG. 4, and the control part 41 and the radioactivity calculation part 42 shown in FIG.

First, as shown in FIGS. 1 to 3, the first measurement unit 11 is provided on a base 12 installed on the floor 110, and includes a mounting section 13 for mounting the rectangular storage container 100 and a measuring unit 11 for measuring. and a moving unit 14 that moves the measuring unit 31 . 1 to 3, X and Y indicate directions orthogonal to each other in the horizontal direction, and Z indicates the vertical direction.

The base 12 has two side portions 12A extending in the X direction and arranged in parallel in the Y direction, and a central portion 12B provided between the side portions 12A.

The mounting portion 13 is arranged in the central portion 12B of the base 12 . The mounting section 13 has a mounting table 13a on which the rectangular storage container 100 is mounted, and a rotation mechanism 13b that rotates the mounting table 13a around a vertical rotation axis C. As shown in FIG. Therefore, the rectangular storage container 100 placed on the placement portion 13 is rotated around the vertical rotation axis C. As shown in FIG. The mounting table 13a mounts the upper outer surface of the rectangular storage container 100 horizontally. The rotating mechanism 13b rotates the square storage container 100 and stops the two side outer surfaces of the square storage container 100 facing in opposite directions at positions along the X direction. The rotation mechanism 13 b has, for example, a motor as a drive source, and the motor is controlled by the control section 41 . The placing section 13 includes a weight measuring section 13c. The weight measurement unit 13c measures the weight of the rectangular storage container 100 placed on the placement table 13a. The measured weight data is stored in the storage device of the control unit 41 and output to the radioactivity calculation unit 42 .

The moving part 14 is arranged on the side part 12</b>A of the base 12 . The moving part 14 has a rail 14a extending in the X direction on the side part 12A of the base 12 and a moving body 14b moving in the X direction along the rail 14a. Further, although not shown in the drawing, the moving part 14 has a moving mechanism for moving the moving body 14b in the X direction along the rail 14a. The moving mechanism has, for example, a motor as a driving source, and the motor is controlled by the control section 41 . A measuring unit 31 is attached to the moving body 14b. Therefore, the measuring section 31 is provided so as to be movable in the X direction by the moving section 14 .

The measurement unit 31 has a smear measurement unit 32, a radiation measurement unit 33, and a radiation dose detection unit 34, as shown in FIG.

The smear measuring section 32 measures the surface contamination of the rectangular storage container 100 . The smear measuring unit 32 includes a first roll 32b around which the filter cloth 32a is wound, a second roll 32c around which the filter cloth 32a is wound, and a filter that is pulled out from the first roll 32b and wound around the second roll 32c. The filter cloth 32a is sent by a plurality of guide rollers 32d for guiding the cloth 32a. The smear measuring section 32 also has a pressing mechanism 32e that presses the filter cloth 32a against the outer surface of the rectangular storage container 100 while being pulled out from the first roll 32b and wound up on the second roll 32c. In addition, the smear measuring part 32 adheres to the filter cloth 32a after being pressed against the outer surface of the rectangular storage container 100 by the pressing mechanism 32e while being pulled out from the first roll 32b and being wound up on the second roll 32c. It has a contamination detector 32f for detecting the radiation of soil (sample) that has been applied. A plastic scintillator detector, for example, is used as the contamination detector 32f. The smear measuring section 32 also has a frame 32g that supports a first roll 32b, a second roll 32c, a guide roller 32d, a pressing mechanism 32e, and a contamination detector 32f. The results detected by the contamination detector 32 f are stored in the storage device of the control unit 41 and output to the radioactivity calculation unit 42 .

The radiation measurement unit 33 detects radiation. In the present embodiment, for example, gamma rays are used as the object of measurement, and a NaI scintillation detector or the like is used. The radiation measurement unit 33 is housed in a casing 35 . The results detected by the radiation measurement unit 33 are stored in the storage device of the control unit 41 and output to the radioactivity calculation unit 42 .

The radiation dose detection unit 34 detects the radiation dose. In this embodiment, for example, the object to be measured is γ-rays, and a Si semiconductor detector or the like is used. The radiation dose detection unit 34 is housed in the casing 35 together with the radiation measurement unit 33 . The results detected by the radiation dose detector 34 are stored in the storage device of the controller 41 and output to the radioactivity calculator 42 . If the radiation measurement unit 33 can be installed on the entire outer surface of the rectangular storage container 100, the radiation dose detection unit 34 may not be provided because the radiation measurement unit 33 can also be used for dose measurement.

A frame 32g of the smear measuring unit 32 is attached to a casing 35 that houses the radiation measuring unit 33 and the radiation dose detecting unit 34. As shown in FIG. That is, the measurement unit 31 is integrally provided with a smear measurement unit 32, a radiation measurement unit 33, and a radiation dose detection unit . A frame 32 g of the smear measuring section 32 is attached to the casing 35 via rails 36 . The rail 36 is a direction A in FIG. 4 which is a direction crossing (perpendicular to) the direction in which the filter cloth 32a is sent from the first roll 32b to the second roll 32c in the smear measuring section 32 and which is the width direction of the filter cloth 32a. It extends to The smear measuring section 32 is provided movably along the direction A in which the rail 36 extends. Although not shown in the drawing, the smear measuring section 32 is provided with a moving mechanism for moving along the rail 36 . The moving mechanism has, for example, a motor as a driving source, and the motor is controlled by the control section 41 . The casing 35 is attached to the moving body 14 b of the moving part 14 . Therefore, the measuring section 31 is attached to the moving body 14 b of the moving section 14 .

In the first measurement unit 11, the moving body 14b moves the rectangular storage container 100 placed on the mounting part 13 along the upper outer surface and the side outer surface of the rectangular storage container 100 so that it can move in the X direction. It is configured in a gate shape that surrounds in the direction and Y direction, and both lower ends are supported by rails 14a. As shown in FIGS. 1 to 3, the measuring unit 31 for the moving body 14b has a gate-shaped upper part facing the upper outer surface of the rectangular storage container 100 and a side outer surface facing the rectangular storage container 100. It is placed on the side of the portal. The measuring unit 31 is arranged so that the B direction shown in FIG. 4 coincides with the X direction in which the moving body 14b moves.

The measurement unit 31 arranged on the gate-shaped upper part of the moving body 14b is arranged so that the smear measurement unit 32 presses the filter cloth 32a downward by the pressing mechanism 32e. The smear measuring unit 32 is arranged so that the A direction, which is the moving direction of the rail 36, coincides with the Y direction. A plurality of smear measuring units 32 (two in this embodiment) are arranged in the A direction, which is the moving direction that coincides with the Y direction.

Moreover, as shown in FIG. 1, the radiation measuring section 33 is arranged with the detector facing downward in the measuring section 31 arranged on the gate-shaped upper portion of the moving body 14b. In the radiation measurement unit 33, a plurality of detectors (six in this embodiment) are arranged in the Y direction.

Therefore, the measuring unit 31 arranged on the gate-shaped upper part of the moving body 14b moves along the upper outer surface of the rectangular storage container 100 by moving in the X direction together with the moving body 14b. As a result, the measurement unit 31 can move in the X direction along the upper outer surface of the rectangular storage container 100 to measure the contamination on the upper outer surface of the rectangular storage container 100 , and transmit through the upper outer surface of the rectangular storage container 100 . Radiation can be detected. Further, by moving the smear measuring section 32 in the Y direction and by arranging a plurality of smear measuring sections 32 in the Y direction, it is possible to measure the contamination of the upper and outer surface of the rectangular storage container 100 over a wide range in the Y direction. In addition, since a plurality of radiation measuring units 33 are arranged in the Y direction, it is possible to detect a wide range of radiation in the Y direction on the upper outer surface of the rectangular storage container 100 .

On the other hand, the measurement unit 31 arranged on the side of the portal of the moving body 14b is arranged so that the smear measurement unit 32 presses the filter cloth 32a laterally (in the Y direction) by the pressing mechanism 32e. The smear measuring unit 32 is arranged so that the A direction, which is the moving direction of the rail 36, coincides with the Z direction. In addition, a plurality of smear measuring units 32 (two in this embodiment) are arranged in the A direction, which is the movement direction coinciding with the Z direction.

In addition, as shown in FIG. 2, the measuring unit 31 arranged on the side of the portal of the moving body 14b is arranged with the radiation measuring unit 33 facing the detector sideways (in the Y direction). In addition, the radiation measurement unit 33 has a plurality of detectors (six in this embodiment) arranged in the Z direction.

Therefore, the measuring unit 31 arranged on the side of the portal of the moving body 14b moves along the lateral outer surface of the rectangular storage container 100 by moving in the X direction together with the moving body 14b. As a result, the measurement unit 31 can move in the X direction along the lateral outer surface of the rectangular storage container 100 to measure the contamination on the lateral outer surface of the rectangular storage container 100 , and the contamination is transmitted through the lateral outer surface of the rectangular storage container 100 . Radiation can be detected. Further, by moving the smear measuring section 32 in the Z direction and by arranging a plurality of smear measuring sections 32 in the Z direction, it is possible to measure the wide range of contamination of the side outer surface of the rectangular storage container 100 in the Z direction. In addition, since a plurality of radiation measuring units 33 are arranged in the Z direction, it is possible to detect a wide range of radiation in the Z direction of the lateral outer surface of the rectangular storage container 100 .

Also, the first measurement unit 11 rotates the rectangular storage container 100 on the mounting portion 13 . Therefore, by rotating the rectangular storage container 100 by 90 degrees, the measuring unit 31 arranged on the gate-shaped side of the moving body 14b moves in the X direction along the other side outer surface of the rectangular storage container 100. do. As a result, the measuring unit 31 can move in the X direction along the side outer surface of the rectangular storage container 100 to measure the contamination on the other side outer surface of the rectangular storage container 100, and the other side of the rectangular storage container 100 can be measured. Radiation transmitted through the outer surface can be detected.

Note that the measuring units 31 may be arranged on both sides of the gate shape of the moving body 14b, so that the measuring units 31 move in the X direction along the two opposing side outer surfaces of the rectangular storage container 100. It is possible to move and measure the contamination on the two opposite side outer surfaces of the rectangular storage container 100 and detect the radiation transmitted from the two opposite side outer surfaces of the rectangular storage container 100 .

Next, as shown in FIGS. 5 and 6, the second measurement unit 21 is provided on a base 22 installed on the floor 110, and includes a mounting portion 23 for mounting the rectangular storage container 100, A measuring unit 31 and a moving unit 24 for moving the measuring unit 31 are provided. 5 and 6, X and Y indicate directions orthogonal to each other in the horizontal direction, and Z indicates the vertical direction.

The base 22 has two side portions 22A extending in the X direction and arranged in parallel in the Y direction.

The mounting portion 23 is arranged between both side portions 22A of the base 22 . The mounting portion 23 is configured in a frame shape so as to support the periphery of the lower outer surface of the rectangular storage container 100 . That is, the mounting portion 23 mounts the rectangular storage container 100 so that the lower outer surface of the rectangular storage container 100 is opened.

The moving parts 24 are arranged on both sides 22A of the base 22 . The moving part 24 has rails 24a extending in the X direction on both sides 22A of the base 22, and a moving body 24b moving in the X direction along the rails 24a. Although not shown in the figure, the moving part 24 has a moving mechanism for moving the moving body 24b in the X direction along the rails 24a. The moving mechanism has, for example, a motor as a driving source, and the motor is controlled by the control section 41 . A measuring unit 31 is attached to the moving body 24b. Therefore, the measuring section 31 is provided so as to be movable in the X direction by the moving section 24 . The measurement unit 31 is arranged so that the B direction shown in FIG. 4 coincides with the X direction in which the moving body 24b moves.

As shown in FIG. 6, the measuring section 31 is arranged so that the smear measuring section 32 presses the filter cloth 32a upward by the pressing mechanism 32e. The smear measuring unit 32 is arranged so that the A direction, which is the moving direction of the rail 36, coincides with the Y direction. A plurality of smear measuring units 32 (two in this embodiment) are arranged in the A direction, which is the moving direction that coincides with the Y direction.

Moreover, as shown in FIG. 5, the radiation measurement unit 33 is arranged with the detector facing upward. In the radiation measurement unit 33, a plurality of detectors (four in this embodiment) are arranged in the Y direction.

By moving in the X direction together with the moving body 24b, the measuring unit 31 moves along the lower outer surface of the rectangular storage container 100 so as to pass under it. As a result, the measurement unit 31 can move in the X direction along the lower outer surface of the rectangular storage container 100 to measure the contamination on the lower outer surface of the rectangular storage container 100 , and transmit through the lower outer surface of the rectangular storage container 100 . Radiation can be detected. Further, by moving the smear measuring section 32 in the Y direction and by arranging a plurality of smear measuring sections 32 in the Y direction, it is possible to measure the contamination of the lower outer surface of the rectangular storage container 100 over a wide range in the Y direction. In addition, since a plurality of radiation measuring units 33 are arranged in the Y direction, it is possible to detect a wide range of radiation in the Y direction from the lower outer surface of the rectangular storage container 100 .

The radioactivity measurement device according to the above-described embodiment has a control section 41 and a radioactivity amount calculation section 42 . The control unit 41 is an arithmetic device including a CPU (Central Processing Unit), a storage device, and the like. 31 , the moving unit 24 and the measuring unit 31 in the second measuring unit 21 , and the radioactivity amount calculating unit 42 . In the radioactivity measuring device, the control unit 41 and the radioactivity amount calculating unit 42 may be integrated into one computing device, that is, hardware may be shared. That is, each process may be processed in parallel by one CPU.

The operation of the radioactivity measuring device according to the above embodiment will be described. FIG. 7 is a flow chart showing the operation of the radioactivity measuring device according to the embodiment of the present invention.

The processing shown in FIG. 7 can be realized by the control unit 41 controlling the operation of each unit. First, the rectangular storage container 100 is placed on the mounting table 13a of the mounting section 13 of the first measuring unit 11 by a crane or the like (step S1). The control unit 41 detects that the rectangular storage container 100 has been placed on the mounting table 13a by detecting the weight of the weight measuring unit 13c. The control unit 41 measures the weight of the rectangular storage container 100 using the weight measurement unit 13c (step S2).

After that, the control section 41 moves the measuring section 31 by the moving section 14 in the first measuring unit 11, and measures the radiation of the upper outer surface and the side outer surface of the rectangular storage container 100 (step S3). Further, the control section 41 rotates the rectangular storage container 100 by the rotation mechanism 13b of the mounting section 13 in the first measurement unit 11 (step S4). Specifically, the rotating mechanism 13b of the mounting portion 13 rotates the rectangular storage container 100 by 90 degrees. After that, the control section 41 moves the measuring section 31 by the moving section 14 in the first measuring unit 11, and measures the radiation of the other side outer surface of the rectangular storage container 100 (step S5). By the operations of steps S4 and S5, the radiation on the four lateral outer surfaces of the rectangular storage container 100 is measured.

After that, the rectangular storage container 100 is placed on the mounting portion 23 of the second measuring unit 21 by a crane or the like (step S6). The control unit 41 detects that the rectangular storage container 100 has been placed on the placement unit 23 when detecting an operation input by the operator indicating that the rectangular storage container 100 has been placed. After that, the control section 41 moves the measuring section 31 by the moving section 24 in the second measuring unit 21, and measures the radiation of the lower outer surface of the rectangular storage container 100 (step S7). Thereby, the radiation on all the six surfaces of the rectangular storage container 100 is measured.

As described above, the first measurement unit 11 of the radioactivity measuring apparatus of the present embodiment described above is a radioactivity measuring apparatus for measuring the radiation of radioactive waste stored in the rectangular storage container 100. A measurement unit 31 integrally provided with a smear measurement unit 32 for measuring surface contamination of the container 100 and a radiation measurement unit 33 for measuring radiation of radioactive waste, and a measurement unit 31 along the outer surface of the rectangular storage container 100 and a moving unit 14 for moving the .

Further, the radioactivity measuring method by the first measuring unit 11 of the radioactivity measuring apparatus of the present embodiment is a radioactivity measuring method for measuring the radiation of the radioactive waste stored in the rectangular storage container 100. A measuring unit 31 integrally provided with a smear measuring unit 32 for measuring surface contamination of the storage container 100 and a radiation measuring unit 33 for measuring the radiation of radioactive waste is moved along the outer surface of the rectangular storage container 100. Including the step of measuring the radiation.

The rectangular storage container 100 cannot be measured while being rotated unlike a drum-shaped storage container. Therefore, according to the first measurement unit 11 of the radioactivity measuring apparatus of the present embodiment and the radioactivity measuring method by the first measurement unit 11 of the radioactivity measuring apparatus of the present embodiment, the surface contamination of the rectangular storage container 100 can be A measurement unit 31 integrally provided with a smear measurement unit 32 for measurement and a radiation measurement unit 33 for measuring the radiation of radioactive waste is moved along the outer surface of the rectangular storage container 100 to measure the radiation. Therefore, a plurality of measurements can be performed at the same time, and the operating time (measurement time) in measuring the rectangular storage container 100 can be minimized. A measurement unit 31 integrally provided with a smear measurement unit 32 for measuring surface contamination of the rectangular storage container 100 and a radiation measurement unit 33 for measuring the radiation of radioactive waste is installed along the outer surface of the rectangular storage container 100. Since the radiation is measured by moving the measuring unit 31 by moving the square storage container 100 to a plurality of measuring positions, the size of the apparatus can be reduced.

Moreover, in the first measurement unit 11 of the radioactivity measurement device of the present embodiment, the measurement section 31 includes a radiation dose detection section 34 .

Therefore, the radiation dose can also be detected by the radiation dose detection unit 34 at the same time.

In addition, the first measurement unit 11 of the radioactivity measuring apparatus of the present embodiment further includes a placement section 13 on which the rectangular storage container 100 is placed and rotated around the vertical rotation axis C. As shown in FIG. Further, in the radioactivity measuring method by the first measuring unit 11 of the radioactivity measuring apparatus of the present embodiment, after rotating the rectangular storage container 100 around the vertical rotation axis C, the measuring part 31 is moved to Including the step of measuring the radiation.

Therefore, by rotating the rectangular storage container 100 , the measurement unit 31 can move along a large number of outer surfaces of the rectangular storage container 100 , and can measure the radiation of a large number of outer surfaces of the rectangular storage container 100 .

In addition, the second measurement unit 21 of the radioactivity measuring device of the present embodiment is a radioactivity measuring device that measures the radiation of the radioactive waste stored in the rectangular storage container 100, and the surface of the rectangular storage container 100 A measurement unit 31 integrally provided with a smear measurement unit 32 for measuring contamination and a radiation measurement unit 33 for measuring the radiation of radioactive waste, and a movement for moving the measurement unit 31 along the outer surface of the rectangular storage container 100 a portion 14;

Further, the radioactivity measuring method by the second measuring unit 21 of the radioactivity measuring apparatus of the present embodiment is a radioactivity measuring method for measuring the radiation of the radioactive waste stored in the rectangular storage container 100. A measuring unit 31 integrally provided with a smear measuring unit 32 for measuring surface contamination of the storage container 100 and a radiation measuring unit 33 for measuring the radiation of radioactive waste is moved along the outer surface of the rectangular storage container 100. Including the step of measuring the radiation.

Therefore, according to the second measurement unit 21 of the radioactivity measuring apparatus of the present embodiment and the radioactivity measuring method by the second measurement unit 21 of the radioactivity measuring apparatus of the present embodiment, the surface contamination of the rectangular storage container 100 can be A measurement unit 31 integrally provided with a smear measurement unit 32 for measurement and a radiation measurement unit 33 for measuring the radiation of radioactive waste is moved along the outer surface of the rectangular storage container 100 to measure the radiation. Therefore, a plurality of measurements can be performed at the same time, and the operating time (measurement time) in measuring the rectangular storage container 100 can be minimized. A measurement unit 31 integrally provided with a smear measurement unit 32 for measuring surface contamination of the rectangular storage container 100 and a radiation measurement unit 33 for measuring the radiation of radioactive waste is installed along the outer surface of the rectangular storage container 100. Since the radiation is measured by moving the measuring unit 31 by moving the square storage container 100 to a plurality of measuring positions, the size of the apparatus can be reduced.

Moreover, in the second measurement unit 21 of the radioactivity measurement device of the present embodiment, the measurement section 31 includes a radiation dose detection section 34 .

Therefore, the radiation dose can also be detected by the radiation dose detection unit 34 at the same time.

Further, the radioactivity measuring apparatus of the present embodiment has a mounting portion 13 on which the rectangular storage container 100 is mounted and rotated around a vertical rotation axis C. A first measuring unit 11 that moves the measuring part 31 along the upper outer surface and each side outer surface of the rectangular storage container, and a second measuring unit 21 that moves the measuring part 31 along the lower outer surface of the rectangular storage container 100. ,including.

Therefore, the first measuring unit 11 moves the measuring part 31 along the upper outer surface and each side outer surface of the rectangular storage container, and the second measuring unit moves the measuring part 31 along the lower outer surface of the rectangular storage container 100. 21 and , it is possible to measure the radiation of all the six outer surfaces of the rectangular storage container 100 .

[Radioactivity evaluation method]
FIG. 8 is a flow chart showing the radioactivity evaluation method according to this embodiment. FIG. 9 is a graph showing an example of radiation measurement results. FIG. 10 is a graph showing an example of a correction curve for radiation source uneven distribution in setting the second safety factor of the radioactivity evaluation method according to the present embodiment.

The radioactivity evaluation method of this embodiment is performed by the treatment shown in FIG. The treatment shown in FIG. 8 can be realized by executing calculations in the radioactivity amount calculator 42 based on the results detected by the radioactivity measuring device described above.

The radioactivity calculation unit 42 acquires a spectrum for each radiation measurement unit 33 of each measurement unit 31 (step S11), adds up the spectra for each outer surface, and calculates spectra for six surfaces (step S12). That is, the radioactivity calculator 42 analyzes the measurement results of the six outer surfaces and detects the spectrum of each outer surface.

Next, when the radioactivity calculation unit 42 detects the spectra for the six planes, the spectra for the six planes are averaged to obtain one spectrum (step S13). That is, the radioactivity calculation unit 42 calculates the average spectrum of the six outer surfaces from the radiation spectrum detection results obtained in step S12.

Next, the radioactivity calculator 42 calculates the average count rate n of the target radioactive substances (Cs-137, Co-60, Co-58) based on the average spectra of the six planes (step S14). Specifically, the radioactivity calculator 42 calculates the background, the net peak count rate of 0.662 MeV, and the band count rate of Cs-137. In addition, the radioactivity calculation unit 42 has a Co-60 background of 1.17 MeV, a net peak count rate of 1.17 MeV, a background of 1.33 MeV, a net peak count rate of 1.33 MeV, band area count Calculate the rate. In addition, the radioactivity calculation unit 42 calculates the net peak count rate of Co-58 background and 0.811 MeV.

Next, the radioactivity calculator 42 sets a correction coefficient ε using the value calculated in step S14 (step S15). A correction factor ε is derived from the ratio of the Compton scattering component and the peak count. In this embodiment, as shown in FIG. 9, the peak count is from the 1.17 MeV γ-ray Compton end of Co-60 to the 1.33 MeV γ-ray peak end. This is because the square storage container 100 is expected to have a larger count than the conventional drum type, and the peak region minimizes the counting error. The Compton edge of 1.17 MeV of Co-60 is theoretically 1.074 MeV, and the peak upper edge of Cs-137 of the NaI scintillation detector of the radiation measurement unit 33 is 0.72 MeV in an actual example. Then, for Co-60, for example, the band/peak ratio (B/P ratio=band region count rate/1.33 MeV peak count rate) is observed. Subsequently, as shown in FIG. 10, the peak count with the self-shielding effect added is calculated from the count of the peak region based on the observed B/P ratio and the predetermined correlation curve. The peak of the correlation curve is the count for which the conversion coefficient CF is set, and the correction coefficient ε corresponds to the correction amount for correcting the peak count of the correlation curve by adding the self-shielding effect. That is, the ratio of the peak area to the Compton area is taken, and the self-shielding effect is corrected by the correction coefficient ε according to the ratio. The conversion factor CF can be calculated by interpolating a conversion factor table prepared in advance (by measuring a simulated object using an actual machine) using the average density and storage height of radioactive waste (step S16). Therefore, the average counting rate n calculated in step S14 is multiplied by the correction factor ε and the conversion factor CF (step S17).

Further, step S17 is multiplied by the first safety factor SF1 (step S18) and further multiplied by the second safety factor SF2 (step S19) to calculate the amount of radioactivity A and perform radioactivity evaluation (step S20). . That is, the amount of radioactivity A is obtained by the following formula (1).

Radioactivity A = Counting rate n x Conversion factor CF x First safety factor SF1 x Second safety factor SF2 x Correction factor ε (1)

Amount of radioactivity A: Amount of radioactivity (Bq) inside square storage container 100
Count rate n: average count rate (cps) of the entire detector of the radiation measurement unit 33
Conversion factor CF: Radioactivity conversion factor (Bq/cps)
First safety factor SF1: Safety factor against uneven distribution of density (uneven distribution of contamination inside the rectangular storage container 100) Second safety factor SF2: Safety factor against uneven distribution of radiation sources Correction factor ε: Factor for correcting the self-shielding effect

The first safety factor SF1 and the second safety factor SF2 will be described below. FIG. 11 is a flow chart showing the setting of the first safety factor in the radioactivity evaluation method according to this embodiment. FIG. 12 is a model diagram of a rectangular storage container in setting the first safety factor of the radioactivity evaluation method according to this embodiment. FIG. 13 is a model diagram of the first radiation transmittance in setting the first safety factor in the radioactivity evaluation method according to this embodiment. FIG. 14 is a model diagram of the second radiation transmittance in setting the first safety factor in the radioactivity evaluation method according to this embodiment. FIG. 15 is a graph showing an example of uneven radiation source distribution in setting the second safety factor in the radioactivity evaluation method according to this embodiment. FIG. 16 is a graph showing an example of analysis results in setting the second safety factor in the radioactivity evaluation method according to this embodiment.

The first safety factor SF1 is a safety factor based on uneven distribution of internal contamination and density uneven distribution. To set the first safety factor SF1, as shown in FIG. 11, first, the weight of the contents of the rectangular storage container 100 and the weight of mortar are obtained (step S31). Content weight and mortar weight are controlled and known values. As shown in the model of FIG. 12, the uneven distribution of density is the total weight of the contents excluding the thickness (0.05 m) of the rectangular storage container 100 and the weight of the mortar. , along the inner surface of the rectangular storage container 100 like a lining shield, and to surround the mortar layer C all around. Under this assumption, the thickness TM of the metal layer _M is calculated by the following formula (2) in a similar shape to the rectangular storage container 100 (step S32).

T _M = {L-(V-W _M /ρ _M ) ^(1/3) } (2)

L: Inner dimension of square storage container V: Volume of square storage container W _M : Weight of metal layer ρ _M : Density of metal layer

Also, the thickness TC of the mortar layer _C is calculated by the following formula (3) (step S33).

T _C =(L−2·T _M ) (3)

Next, assuming that the radiation source is _uniformly distributed in the rectangular storage container 100, an approximate model is created as shown in FIG. It is calculated by the following formula (4) (step S34). The part indicated by " _x " in FIG. 13 is the evaluation point of the first radiation transmittance Ra.

μ _M : Linear attenuation coefficient in metal layer μ _C : Linear attenuation coefficient in mortar layer

Next, as in the model shown in FIG. 14, the bulk density (mixed layer of metal layer M and mortar layer C) and the second radiation transmittance R _b in the case of a point radiation source are calculated by the following formula (5) (step S35). The part indicated by "x" in FIG. 14 is the evaluation point of the second radiation transmittance _Rb .

μ _B : linear attenuation coefficient in mixed layer of metal layer and mortar layer

Then, the first safety factor SF1 is calculated by the following formula (6) from the first radiation transmittance _Ra and the second radiation transmittance _Rb (step S36).

SF1=R _b /R _a (6)

The second safety factor SF2 is the case where the radiation sources a and b are unevenly distributed in the homogeneous inside of the rectangular storage container 100 as shown in FIG. It is set to a fixed value of 4.2 so as not to underestimate from the error analysis results for various radiation source position patterns. In the error analysis, the difference between the amount of radioactivity obtained by the evaluation method described in paragraph [0064] and the amount of radioactivity set is obtained as an error from the values obtained in the response simulation of each detector.

As described above, the radioactivity evaluation method of the present embodiment is a radioactivity evaluation method for evaluating the radioactivity of the radioactive waste stored in the rectangular storage container 100, and includes a step of detecting radiation and a process of internal contamination. A step of obtaining a first safety factor SF1 based on the uneven distribution (density uneven distribution), a step of obtaining a second safety factor SF2 based on the uneven distribution of the radiation source, and the first safety factor SF1 and the second safety factor SF2 detected using and determining the amount of radioactivity of the radiation.

Therefore, by obtaining the amount of radioactivity detected using the first safety factor SF1 based on the uneven distribution of internal contamination and the second safety factor SF2 based on the uneven distribution of the radiation source, radioactive waste stored in the rectangular storage container 100 It is possible to easily evaluate the amount of radioactivity of an object while considering uneven distribution of density and uneven distribution of radiation sources.

In addition, in the radioactivity evaluation method of the present embodiment, the first safety factor SF1 is the first radiation penetration in the model in which the radioactive waste (metal layer M) is installed on the inner surface of the rectangular storage container 100 in the form of a lining. It can be determined from the transmittance ratio between the radioactivity R _a and the second radiation transmittance R _b for a uniform radioactivity distribution in the case of bulk density and homogeneity.

Moreover, in the radioactivity evaluation method of the present embodiment, the second safety factor SF2 is a fixed value obtained from the analysis result of the uneven distribution pattern of the radiation source in a system without uneven distribution of density.

By the way, in the radioactivity evaluation method, when no radiation is detected, that is, when the radiation is below the detection limit, the lower limit of detection radioactivity _AL , which is the detection limit value, is calculated.

FIG. 17 is a flow chart showing the radioactivity evaluation method when the radioactivity evaluation method according to the present embodiment is below the detection limit. FIG. 18 is a model diagram of a rectangular storage container in the case of below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 19 is a model diagram of an example of a radiation source assumed to be below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 20 is a model diagram of an example of a radiation source assumed in the case of below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 21 is a model diagram of an example of a radiation source assumed in the case of below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 22 is a model diagram of an example of a radiation source assumed to be below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 23 is a table comparing the uniform radiation source model and the plane radiation source model in the case of below the detection limit of the radioactivity evaluation method according to this embodiment. FIG. 24 is a graph of an example of an approximation curve for setting a conversion factor in the case of below the detection limit of the radioactivity evaluation method according to this embodiment.

As shown in FIG. 17, first, an evaluation model is set (step S41). The basic evaluation model is a homogeneously distributed bulk density model as described above, but when the radiation is below the detection limit, no significant response is obtained from the detection, so the radiation source distribution cannot be corrected. Therefore, when evaluating on the maintenance side, a model in which a point radiation source exists in the center of the rectangular storage container 100 is used, resulting in an excessively conservative conversion of the amount of radioactivity. Therefore, in this embodiment, excessive conservatism is eliminated.

In the bulk density model, the case where the radioactivity conversion is on the non-safe side is considered to be the state where density unevenness exists. Since each measurement value of the radiation measurement unit 33 is averaged, a slight deviation of the density distribution can be absorbed by the bulk density model. However, in the case of the detection limit or less, as shown in FIG. cannot be absorbed by Therefore, such a storage state is used as an evaluation model. Specifically, as shown in FIG. 18, the metal layer (metal mass) M, which is the content, is placed on one inner surface of the rectangular storage container 100, except for the thickness (0.05 m) of the rectangular storage container 100. , the mortar layer C is present on the other.

In addition, there are the following types of radiation sources.
(1) A point radiation source that exists in the center of a metal mass (2) A uniform radiation source that is activated and uniformly distributed (3) A plane radiation source that only the surface is contaminated (4) A penetrating pinhole is contaminated radiation source

Here, when assuming dismantling waste such as metal lumps among the equipment installed in the nuclear power plant, the shapes shown in FIGS. 19 to 22 are conceivable. FIG. 19 shows a morphology in which the inner surface of the through hole is contaminated. FIG. 20 shows a morphology in which the inner surface is contaminated with a portion of a fully activated container. FIG. 21 shows a morphology in which the entirety is activated and the gap where the plates are partially joined together is contaminated. FIG. 22 shows a morphology in which the inner surface of a portion of the container is contaminated.

The above (1) and (4) are the equipment installed in the nuclear power plant, and are excluded because they are unlikely to be objects when assuming dismantling waste such as metal lumps.

On the other hand, regarding the above (2) and (3), the uniform radiation source of (2) has a uniform distribution of contamination as shown in FIG. If is regarded as a uniform radiation source, it is a form that is on the maintenance side, and as shown in Fig. 21, it is equipment installed inside the nuclear reactor, and since activation is superior to contamination, it can be regarded as a uniform radiation source. there is a form. In addition, as shown in FIG. 22, the surface radiation source of (3) is, for example, a part of a thick container with a contaminated inner surface.

Regarding these uniform radiation sources and surface radiation sources ^, as shown in the simple calculation example shown in FIG. It is on the conservative side due to its low , and high self-shielding. Therefore, in the conversion evaluation of the detection limit, as shown in FIG. 18, for the radiation source, a surface radiation source model is set in which the contaminated surface R, which is a surface radiation source, faces the inside of the container. 23, the ray bundle (point P) is a point that coincides with the contaminated surface R of the metal layer (metal lump) M in the y direction, as shown in FIG.

After the plane source model is set (step S41), as shown in FIG. 17, the weight of the contents of the rectangular storage container 100 and the weight of mortar are obtained (step S42), and the size of the metal layer is calculated (step S43). ). Content weight and mortar weight are controlled and known values. The size of the metal layer is calculated by the formula (2) described above. After that, a conversion factor CF _ND is set (step S44). The conversion factor CF _ND is set from a database of conversion factors CF _ND according to the weight of metal lumps or an approximate curve as shown in FIG. 24 by analysis or test in advance. After that, the lower detection limit amount of radioactivity _AL is calculated by the following formula (7) (step S45).

Detection limit radioactivity amount A _L = detection limit count rate nd × conversion factor CF _ND (7)

The detection limit count rate nd employs the total gross count rate instead of peak area counts.

As described above, in the radioactivity evaluation method of the present embodiment, when no radiation is detected, the metal lumps are unevenly distributed, and the surface of the metal lumps facing the inside of the rectangular storage container 100 is the contaminated surface R. It includes the steps of setting a model and calculating the lower limit of detectable radioactivity _AL .

Therefore, excessive conservativeness can be eliminated by setting the plane source model and calculating the lower detection limit of radioactivity _AL .

In addition, the radioactivity evaluation method when radiation is not detected is not limited to the method of setting the first safety factor SF1 and the second safety factor SF2 as described above. It can also be applied to other radioactivity evaluation methods.

11 first measurement unit 13 placement section 14 moving section 21 second measurement unit 23 placement section 24 moving section 31 measurement section 32 smear measurement section 33 radiation measurement section 34 radiation dose detection section 41 control section 42 radioactivity amount calculation section 100 angle Mold storage container A Amount of radioactivity A _L detection limit amount of radioactivity R _a First radiation transmittance R _b Second radiation transmittance SF1 First safety factor SF2 Second safety factor

Claims (11)

A radioactivity evaluation method for evaluating the radioactivity of radioactive waste stored in a rectangular storage container, comprising the steps of detecting radiation;
A step of obtaining a first safety factor based on uneven distribution of internal contamination;
A step of obtaining a second safety factor based on the uneven distribution of the radiation source;
A step of determining the amount of radioactivity of the detected radiation using the first safety factor and the second safety factor;
Radioactivity evaluation method, including The first safety factor is the first radiotransmittance in a model in which the radioactive waste is lined on the inner surface of the square storage container, and the radioactivity uniform distribution in the case of uniform bulk density. 2. The radioactivity evaluation method according to claim 1, wherein the radioactivity evaluation method is determined from the transmittance ratio with the second radiation transmittance. 3. The radioactivity evaluation method according to claim 1 or 2, wherein said second safety factor is a fixed value obtained from analysis results of uneven distribution patterns of radiation sources in a system in which density is not unevenly distributed. If no radiation was detected,
4. The method according to any one of claims 1 to 3, further comprising the step of setting a surface radiation source model in which metal lumps are unevenly distributed and the surfaces of said metal lumps facing the inside of said rectangular storage container are contaminated, and calculating a lower detection limit radioactivity amount of radiation. Or radioactivity evaluation method according to one. A radioactivity evaluation method for evaluating the radioactivity of radioactive waste stored in a rectangular storage container, comprising a step of detecting radiation,
If no radiation was detected,
A radioactivity evaluation method, comprising the step of setting a surface radiation source model in which metal lumps are unevenly distributed and the surfaces of the metal lumps facing the inside of the rectangular storage container are contaminated, and calculating a lower detection limit radioactivity amount of radiation. A radioactivity measuring method for measuring the radiation of radioactive waste stored in a rectangular storage container,
A measurement unit integrally provided with a smear measurement unit for measuring surface contamination of the square storage container and a radiation measurement unit for measuring the radiation of the radioactive waste is moved along the outer surface of the square storage container. A method for measuring radioactivity, comprising the step of measuring radiation. 7. The radioactivity measuring method according to claim 6, further comprising the step of rotating said rectangular storage container about a vertical axis of rotation and then moving said measurement unit to measure radiation. A radioactivity measuring device for measuring the radiation of radioactive waste stored in a rectangular storage container,
a measurement unit integrally provided with a smear measurement unit for measuring surface contamination of the rectangular storage container and a radiation measurement unit for measuring radiation of the radioactive waste;
a moving unit that moves the measuring unit along the outer surface of the rectangular storage container;
A radioactivity measuring device. 9. The radioactivity measuring device according to claim 8, wherein said measurement unit includes a radiation dose detection unit. 10. The radioactivity measuring apparatus according to claim 8 or 9, further comprising a mounting section for mounting said rectangular storage container thereon and rotating it around a vertical axis of rotation. having a mounting portion for mounting the rectangular storage container and rotating it around a vertical rotation axis, along the upper outer surface and each side outer surface of the rectangular storage container mounted on the mounting portion; a first measuring unit for moving the measuring part by
a second measuring unit that moves the measuring part along the lower outer surface of the rectangular storage container;
The radioactivity measuring device according to claim 8 or 9, comprising:

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