JP2022062500A - Radioactivity concentration evaluation method - Google Patents

Abstract

To provide a radioactivity concentration evaluation method capable of measuring and evaluating the radioactivity concentration of radioactive waste randomly stored in a container.SOLUTION: The radioactivity concentration evaluation method of radioactive waste includes the steps of: placing radioactive waste in a container; virtually splitting the interior space of the container into plural split areas; irradiating each split area with radiation; measuring weight or concentration of the inner radioactive waste from the permeation amount of the radiation; counting of radiation emitted from radioactive waste for each split area and analyzing the radiation nuclide; and evaluating the radioactivity concentration of the nuclide to be evaluated contained in the radioactive waste from the count value of radiation, the analysis result of radiation nuclide, and the weight or density.SELECTED DRAWING: Figure 8

Description

The present invention relates to a method for evaluating the radioactivity concentration of materials and equipment and waste generated in a nuclear facility.

Conventionally, it is necessary to confirm whether the radioactivity concentration of materials and equipment and waste (hereinafter collectively referred to as "radioactive waste") generated in nuclear facilities is below the default value before disposal. be. Then, low-level radioactive waste having a radioactive concentration of a specified value or less is disposed of by a predetermined method. There is a clearance system for the disposal of radioactive waste. The clearance system is based on the national government for the measurement / evaluation method and measurement / evaluation results of radioactive concentration for radioactive waste that has a low radioactive concentration and does not need to consider the impact 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 dispose of radioactive waste by applying the clearance system, it is necessary to confirm that the radioactive concentration of radioactive waste is below the clearance level that can be disposed of and reused in the same way as general waste. be. The clearance level is sufficiently small compared to the radiation level in nature and is the amount of radiation that does not need to be treated as a radioactive substance for safety. The clearance level is expressed in terms of radioactivity concentration, that is, radioactivity per unit weight (becquerel / gram: Bq / g), and a clearance measuring device approved by the government is used as a method for measuring and evaluating the radioactivity concentration. , Evaluate the radioactivity from the measured radiation and divide by the measured weight to evaluate the radioactivity concentration (Bq / g).

When evaluating the radioactive concentration of radioactive waste, there is a method of storing the radioactive waste in a container and measuring the radiation emitted from the outside of the container. For example, as a prior art of this kind, there is a method of measuring the density of a radioactive substance by irradiating a container filled with a measured object containing a radioactive substance from an external irradiation radiation source with gamma rays (see, for example, Patent Document 1). In this method, the first detection value that measures the sum of the gamma rays caused by the external irradiation radiation source and the gamma rays caused by the object to be measured and the second detection value that measures only the gamma rays emitted from the object to be measured are used. , The density of radioactive substances in the object to be measured is measured.

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

Japanese Unexamined Patent Publication No. 62-91879 Japanese Patent Application Laid-Open No. 2003-75540

By the way, according to the national examination standards, in order to make radioactive waste clearable, the clearance specified for each nuclide, including the measured and evaluated radioactive concentration (Bq / g) and the uncertainty of the result. We want to be below the level. If the uncertainty of the measurement result is large, a part of the quantity assumed to be able to be cleared cannot be cleared and will be disposed of as low-level radioactive waste, which will increase the management cost.

For this reason, in the radioactive concentration evaluation of the clearance level of radioactive waste generated in nuclear facilities, the radioactive waste is stored uniformly in a container such as a predetermined iron box, or the height is placed on a metal mesh tray. While observing the restrictions, the radioactivity concentration is evaluated greatly by arranging them so that they do not overlap and keeping the uncertainty small, and setting the coefficient to convert the radiation count measured in the entire container into radioactivity on the safe side.

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

Temporarily, in order to reduce the time and labor required for the pretreatment work, the radioactive waste should be randomly placed in the container (random means not performing the pretreatment work to evenly arrange the radioactive waste). When stored, the uncertainty of the measurement result becomes large, for example, when the radioactive substance is unevenly attached to a part of the radioactive waste.

Since both Patent Document 1 and Patent Document 2 detect gamma rays of the entire object to be measured filled in the container, the work of filling the container with radioactive waste requires time and labor.

Therefore, an object of the present invention is 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, the radioactivity concentration evaluation method according to the present invention is a radioactivity concentration evaluation method for radioactive waste, in which the radioactive waste is placed in a container and the internal space of the container is virtually created. It is divided into a plurality of regions, each of the divided regions is irradiated with radiation, the weight or density of the radioactive waste inside is measured from the amount of the radiation transmitted, and each of the divided regions is discharged from the radioactive waste. The radiation count and the radioactivity emission nuclei are analyzed, and the radioactivity concentration of the evaluation target nuclei contained in the radioactive waste is evaluated from the radiation count value, the analysis result of the radiation emission nuclei, and the weight or density. "Radiation" in this specification and the documents of the claims includes X-rays, synchrotron radiation, gamma rays and the like.

With this configuration, the radioactive waste in the container is counted by weight or density and radiation in each of multiple divided regions and the radiation nuclide is analyzed, so that even if the radioactive waste is randomly stored in the container. Radiation counts and radioactive nuclides can be properly analyzed. Then, the radioactivity concentration of the nuclide to be evaluated contained in the radioactive waste can be appropriately evaluated from the count value of the radiation, the analysis result of the radiation emitting nuclide, and the weight or density. Therefore, the time and labor required for the work of storing the radioactive waste in the container can be reduced, and the measurement accuracy in the radioactivity concentration measurement can be improved.

Further, the radiation emitted from the radioactive waste is counted by a radiation detector, the radiation emitting nuclei emitted from the radioactive waste are analyzed by a radiation emitting nuclei analyzer, and the radiation obtained by the radiation detector is analyzed. The count for each radioactive nuclei may be obtained from the count value and the result of radiation emission nuclei analysis by the radiation emission nuclei analyzer, and the radiation count may be assigned based on the abundance ratio of the radionuclear species to evaluate the radioactivity. ..

With this configuration, the radiation count value is calculated for the abundance ratio of radionuclides based on the count for each radionuclide obtained from the detection of radiation by the radiation detector and the analysis of the radionuclide emitted by the radionuclide analyzer. By allocating, radioactivity can be evaluated appropriately.

Further, the radioactivity of the nuclide to be evaluated contained in the radioactive waste may be evaluated for each divided region based on the count value of the radiation and the analysis result of the radiation emitting nuclide.

With this configuration, it is possible to evaluate the radiation count value and the radioactivity of the nuclide to be evaluated for each divided region of the radioactive waste in the container.

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

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

Further, based on the weight measurement result for each divided region of the radioactive waste, the attenuation due to the self-absorption of the radiation emitted from the radioactive waste is evaluated, and the attenuation is used for calculating the detection efficiency in the counting of the radiation. It may be reflected.

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

In addition, the count value of the radiation, the detection value of the radiation emitting nuclei species analyzer, the position and distribution of the radioactive substance attached to the radioactive waste in the container, the estimation of the radioactivity, and the weight or the weight of each divided region. From the measurement result of the density, the decay may be reflected in the calculation of the detection efficiency in the counting of the radiation, and the radioactivity concentration conversion coefficient may be set for each of the divided regions.

With this configuration, the count value of radiation, the detection value of the radiation nuclei species analyzer, the position and distribution of radioactive materials attached to the radioactive waste, the estimation of radioactivity, and the weight or density of each divided region. From the measurement results, it is possible to set a radioactivity concentration conversion coefficient that reflects the radiation attenuation in the calculation of the detection efficiency in the radiation count for each divided region.

In addition, the radiation count value counted by the radiation detector, the radiation emission nuclei species analysis result analyzed by the radiation emission nuclei species analyzer, and the measurement result of the weight or density for each division region are combined to obtain the radioactivity concentration. The radiation concentration for each divided region may be evaluated by a conversion coefficient.

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

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

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

According to the present invention, it is possible to provide a radioactivity concentration evaluation method capable of measuring and evaluating the radioactivity concentration of radioactive waste randomly stored in a container. Therefore, it is possible to significantly reduce the time and labor required to store the radioactive waste in the container.

FIG. 1 is a perspective view schematically showing a state in which radioactive waste evaluated by the radioactive concentration evaluation method according to the embodiment of the present invention is stored in a container. FIG. 2 is a plan view showing an example of a divided region in which the container shown in FIG. 1 is virtually divided. FIG. 3 is a side view showing a radioactivity concentration evaluation device that implements the radioactivity concentration evaluation method according to the embodiment of the present invention. FIG. 4 is a plan view showing the radioactivity concentration evaluation device shown in FIG. FIG. 5 is a control block diagram in the radioactivity concentration evaluation device shown in FIG. 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 measuring unit shown in FIG. 3, and FIG. 6A is an example graph showing concentration data. (B) is an example schematically showing the density of the transmitted image. FIG. 7 is a perspective view schematically showing an arrangement example of the radiation detector and the radiation emitting nuclide analyzer shown in FIG. 8 (a) to 8 (d) are plan views showing an example of measuring the radiation dose for each divided region of the container shown in FIG. 2.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following embodiment, the radioactivity concentration evaluation method will be described by taking as an example a radioactivity concentration evaluation device 1 that linearly sends 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 by exemplifying a configuration having a plurality of divided regions A to D in which the internal space is virtually divided into four in a plan view. Further, X-rays will be described as an example of radiation. The concept of the vertical and horizontal directions in this specification and the documents of the scope of patent claims is consistent with the concept of the vertical and horizontal directions in which the moving direction of the container 10 in the radioactivity concentration evaluation device 1 shown in FIG. 1 is the horizontal direction. do.

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

As shown in FIG. 1, as the container 10, for example, an iron box having a vertical and horizontal dimension of 100 cm to 150 cm in a plan view and a height of about 50 cm can be used. Radioactive waste 100 is randomly stored in the main 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% with respect to the total volume of the container 10.

As shown in FIG. 2, in this embodiment, the inside of the container 10 is divided into four divided regions A to D which are virtually divided into four equal parts in a plan view. The divided areas A to D are divided in the circumferential direction by a 90 ° virtual line 15 passing through the center point in a plan view of the container 10. For example, when the vertical and horizontal dimensions of the container 10 are 100 cm, the vertical and horizontal dimensions of each of the divided regions A to D are 50 cm in a plan view. This division example is an example.

As will be described later, X-rays are transmitted from the outside by the weight distribution measuring unit 30 to each of the divided regions A to D of the container 10, and each divided region A to the obtained X-ray transmission amount is used. The weight and density of the radioactive waste 100 inside in D are measured. The method of measuring the weight and density of the radioactive waste 100 from the amount of X-ray transmission will be described later.

By measuring the weight and density of the radioactive waste 100 by the weight distribution measuring unit 30, the difference in the filling density in each of the divided regions 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 regions A to D of the container 10, the radiation dose is measured by the plastic scintillator 55 of the radiation measuring unit 50 and the nuclei composition is measured by the Ge semiconductor detector 56, as will be described later. It will be done. Then, from those measurement data, the radiation dose and the nuclide composition of the internal radioactive waste 100 in each of the divided regions A to D are estimated. The method for estimating the radiation dose and the nuclide composition of the radioactive waste 100 will be described later.

(Radioactivity concentration evaluation device 1)
FIG. 3 is a side view showing a 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 direction to the right direction, the left direction is also referred to as an upstream direction, and the right direction is also referred to as a downstream direction. Further, although these figures show an example in which a plurality of containers 10 are flowing at the same time, the number of containers 10 flowing at the same time in the radioactivity concentration evaluation device 1 is not limited to this example.

As shown in the figure, the radioactivity concentration evaluation device 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 the weight distribution and the radiation are measured for each of the divided areas A to D. That is, as described later, in the weight distribution measuring unit 30 and the radiation measuring unit 50, in this embodiment, the container 10 is rotated by 90 ° by the container rotating unit 40, and each divided region of 1/4 of the container 10 is rotated. It is designed to measure every A to D. Therefore, since the measurement is performed four times for each of the containers 10, the container 10 includes the weight distribution measurement unit 30 and the container rotation unit 40, and the radiation measurement unit 50 and the container rotation unit 40. It is transferred back and forth multiple times between. The flow of rotating the container 10 by 90 ° is shown in FIG. 8 described later.

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

Hereinafter, each unit 20, 30, 40, 50 will be described.

[Weight measurement unit 20]
The weight measuring unit 20 is provided with a container transport unit 22 on the upper part of the gantry 21. The container transport section 22 of this embodiment is a roller chain transport section 23 in which a plurality of rollers are provided in the feed direction. The container 10 is sent in the downstream direction (right direction) by the roller chain transport unit 23. The roller chain transport unit 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 mounted on the container transport unit 22. The weight measuring instrument 25 is supported by a damper 26 provided on the gantry 21. As the weight measuring instrument 25, for example, a load cell method can be used, and an instrument capable of measuring 1500 kgf to 2500 kgf as the maximum measuring capacity can be used. The function of measuring the weight of the container 10 can also be provided in the container rotation unit 40.

[Weight distribution measurement unit 30]
The weight distribution measuring unit 30 is provided with a container transport unit 32 on the upper part of the gantry 31. The container transport unit 32 is also a roller chain transport unit 33 in which a plurality of rollers are provided in the feed direction. Since the weight distribution measuring unit 30 of this embodiment sends the container 10 to the container rotating unit 40 in the downstream direction and reciprocates the container 10 so as to return from the container rotating unit 40, the roller chain transport unit 33 can be driven in forward / reverse rotation. It has become.

The weight distribution measuring unit 30 has a density measuring device for measuring weight or density (hereinafter, also referred to as “weight / density”) for each of the divided regions A to D in which the container 10 is virtually divided into four. ing. As the density measuring instrument, an X-ray measuring instrument is used in this embodiment. The X-ray irradiation unit 35 of the X-ray measuring instrument is arranged so as to irradiate X-rays from above the container 10 toward one of the divided regions A to D. Below the container 10 at the position where the X-ray irradiation unit 35 is arranged, an X-ray detection unit 36 for obtaining an image of the amount of X-rays transmitted through the container 10 is provided. The weight and density of the radioactive waste 100 in the container 10 are measured (understood) in the control device 60 from the amount of X-ray transmission obtained by the X-ray detection unit 36. 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 capable of evaluating an iron-based metal up to a thickness of 100 mm can be used. The tube voltage of the X-ray irradiation unit 35, the rated value of the tube current, and the like 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 from the outside.

[Container rotation unit 40]
The container rotation unit 40 is provided with a container transport portion 42 on the upper part of the gantry 41. The container transport section 42 is also a roller chain transport section 43 in which a plurality of rollers are provided in the feed direction. The container rotation unit 40 of this embodiment reciprocates the container 10 between the weight distribution measurement unit 30 and the radiation measurement unit 50. Therefore, the roller chain transport unit 43 can be driven in the forward and reverse directions.

The container rotation unit 40 is provided with an arrangement changing device 45 for lifting and rotating the container 10 from the roller chain transport unit 43. The arrangement changing device 45 has a contact portion 46 in contact with the lower surface of the container 10 and a jack portion 47 for raising and lowering the contact portion 46. The jack portion 47 has a function of rotating the contact portion 46 at an angle of every 90 °. The jack portion 47 has a function of locking the position of the contact portion 46 each time it is rotated. In this embodiment, in order to sequentially change the positions of the divided regions A to D in which the container 10 is divided into four in the circumferential direction, the container 10 is rotated at 90 °, but the container 10 is divided into two divided regions. In this case, it may be configured to rotate at 180 °. The arrangement changing device 45 may rotate the container 10 at an angle corresponding to the number of virtually divided internal spaces of the container 10.

[Radiation measurement unit 50]
The radiation measurement unit 50 is provided with a container transport unit 52 on the upper part of the gantry 51. The container transport unit 52 is also a roller chain transport unit 53 in which a plurality of rollers are provided in the feed direction. In the radiation measurement unit 50 as well, the roller chain transport unit 53 can be driven in the forward and reverse directions so that the container 10 can be transferred between the container 10 and the container rotation unit 40 in the downstream direction.

The radiation measuring unit 50 measures the composition of the radiation emitting nuclei of the radioactive waste 100 and the plastic scintillator 55 for measuring the radiation amount of the radioactive waste 100 in the container 10 (hereinafter, also simply referred to as “nucleus composition”). A Ge semiconductor detector 56 and the like are provided. The plastic scintillator 55 is a radiation dose measuring instrument, and the Ge semiconductor detector 56 is a radiation emitting nuclei species analyzer.

In this embodiment, the plastic scintillator 55 measures the radiation dose for each of the divided regions A to D in which the container 10 is virtually divided into four. The plastic scintillator 55 has a pair of configurations provided above and below the container 10. As the plastic scintillator 55, a known technique can be adopted.

In this embodiment, the Ge semiconductor detector 56 is arranged so as to measure the radiation emitting nuclide in each of the divided regions A to D different from the divided regions A to D in which the plastic scintillator 55 is arranged. In this embodiment, the Ge semiconductor detector 56 is arranged at the position of the divided region diagonally with the plastic scintillator 55. As the Ge semiconductor detector 56, a known technique can be adopted. In this way, the plastic scintillator 55 and the Ge semiconductor detector 56 are designed to measure each divided region.

The radiation measuring unit 50 is covered with a shielding wall 57 that blocks radiation from the outside so that the radiation does not leak to the outside. A container dispensing unit (not shown) may be provided in the downstream direction of the radiation measuring unit 50.

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

According to the radioactivity concentration evaluation device 1, the following transmission / reception is performed between each unit 20, 30, 40, 50 and the control device 60 (including the data processing unit 61). The configuration shown in FIGS. 3 to 4 will be referred to, and the description including the operation thereof will be described.

The weight measuring unit 20 transmits / receives to / from the control device 60 whether or not the container 10 is arranged at a fixed position. The fixed position arrangement of the container 10 may be such that the position of the container 10 is detected by a sensor. When the container 10 is arranged in a fixed position, the weight measurement is started by the signal from the control device 60. When the weight measurement is completed, the container 10 is sent in the direction of the weight distribution measurement unit 30 by the roller chain transport unit 23. The weight measurement data in the weight measurement unit 20 is sent to the data processing unit 61 and stored in a storage unit (ROM, RAM, etc.). When the data is stored in the data processing unit 61, a signal is sent from the data processing unit 61 to the control device 60, and a signal is output from the control device 60 to send the container 10 to the weight distribution measurement unit 30.

The weight distribution measuring unit 30 transmits / receives to / from the control device 60 whether or not the container 10 is arranged at a fixed position. The fixed position arrangement of the container 10 may be such that the position of the container 10 is detected by a sensor. When the container 10 is arranged at a fixed position, the measurement surfaces (virtually divided surfaces) of the divided regions A to D arranged at the positions of the X-ray irradiation unit 35 are recognized. In this example, the division area A is recognized in order. When the divided region A is recognized, the measurement is started by the signal from the control device 60. As a result, the divided region A is irradiated with X-rays from the X-ray irradiation unit 35, and the transmission amount is obtained by the X-ray detection unit 36. The transmittance obtained by the X-ray detection unit 36 is sent to the data processing unit 61. When the data is stored in the data processing unit 61, a signal is sent from the data processing unit 61 to the control device 60. In this way, when the measurement of the divided region A of the container 10 is completed by the weight distribution measuring unit 30, the control device 60 issues a forward rotation instruction to the roller chain transport unit 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 °, and after the container 10 is lifted by the arrangement changing device 45, the container 10 is rotated by 90 °. When the container 10 is rotated by 90 ° by the container rotation unit 40, a reversal instruction is issued from the control device 60 to the roller chain transport unit 43, and the container 10 is returned to the weight distribution measurement unit 30 in the upstream direction. In the container 10 returned to the weight distribution measuring unit 30, it is recognized that the divided region B is arranged at the position of the X-ray irradiation unit 35, and the divided region B is irradiated with X-rays from the X-ray irradiation unit 35. Then, the transmittance obtained by the X-ray detection unit 36 is sent to the data processing unit 61.

In this way, when the measurement of the divided region B of the container 10 is completed by the weight distribution measuring unit 30, the control device 60 issues a forward rotation instruction to the roller chain transport unit 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 in order by the weight distribution measurement unit 30 for the division region C and the division region D in the same manner as the measurement in the division region B. Will be. Since the measurement of weight and density in each of the divided regions A to D is the same as in FIGS. 8 (a) to 8 (d) described later, detailed description thereof will be omitted.

When the weight / density measurement is completed for all the divided regions A to D, the roller chain transport unit 33 is driven in the forward direction by a signal from the control device, and the container 10 is sent to the container rotation unit 40. In this embodiment, the container 10 sent to the container rotation unit 40 is rotated by 90 ° to return the divided region A to the initial position, and then from the container rotation unit 40 to the radiation measurement unit 50 in the downstream direction. Sent.

The container 10 sent to the radiation measuring unit 50 transmits and receives to / from the control device 60 whether or not the container 10 is arranged at a fixed position. The fixed position arrangement of the container 10 may be such that the position of the container 10 is detected by a sensor. When the container 10 is arranged at a fixed position, it is recognized that the divided region A, which is virtually divided into four, is arranged at the position of the plastic scintillator 55. When the divided region A is recognized, the plastic scintillator 55 starts measuring the radiation dose in the divided region A. Further, in this state, the divided region C is arranged at the position of the Ge semiconductor detector 56, and the Ge semiconductor detector 56 detects the radiation emitting nuclei in the divided region C. The measured value of the radiation dose measured in the divided region A and the detected value of the radiation emitting nuclei detected in the divided region 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 region A and the detection of the radiation emitting nuclide in the divided region C are completed, the control device 60 issues a reversal instruction to the roller chain transport unit 53, and the container 10 becomes 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 arrangement changing device 45. When the container 10 is rotated by the container rotation unit 40 by 90 °, the control device 60 issues a forward rotation instruction to the roller chain transport unit 43, and the container 10 is sent to the radiation measurement unit 50.

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

Then, when the measurement of the radiation dose in the divided region B and the detection of the nuclei species composition in the divided region 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 by 90 ° by the rearrangement 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 division region C and the detection of the radiation emitting nuclide in the division region A are similarly performed. Will be done. After that, the radiation dose for the divided region D and the detection of the radiation emitting nuclide for the divided region B are performed in the same manner.

According to this radioactivity concentration evaluation device 1, in order to evaluate the radioactivity of the radioactive waste 100, the measurement by the Ge semiconductor detector 56, which is a radiation emission nuclei species analyzer that can measure the energy spectrum of gamma rays for each divided region, is performed. By adding it, the abundance ratio of the nuclei to be measured / evaluated can be obtained, and the count value obtained by the total gamma ray measurement can be distributed to each nuclei.

(Evaluation of weight distribution by weight distribution measurement unit 30)
FIG. 6 is a diagram showing data for evaluating the weight and density of radioactive waste 100 from the amount of X-ray transmission in the weight distribution measuring unit 30 shown in FIG. 3, and FIG. 6A is an example graph showing concentration data. Yes, (b) is an example schematically showing the density (gray scale) of the transmitted image. FIG. 6A shows a change in the plate thickness of the radioactive waste 100 and a change in the gray scale concentration.

In the weight distribution measuring unit 30, X-rays are irradiated from the X-ray irradiation unit 35 toward the container 10, and the weight of the radioactive waste 100 in the container 10 is obtained from the amount of X-ray transmission obtained by the X-ray detection unit 36.・ The distribution of density is measured (understood). In FIG. 6, the tube voltage when X-rays are irradiated from the X-ray irradiation unit 35 and the grayscale concentration generated by the permeation amount that changes depending on the density (plate thickness) of the radioactive waste 100 stored in the container 10 are shown. Shows the relationship.

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 and the transmission amount (which can be expressed by the density change of the transmitted image) at that time is tested in advance. From these relationships, a map of the plate thickness in the amount of X-ray transmission is created. From the graph of (a), it can be seen that the transmission image that changes depending on the amount of X-ray transmission has a low 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 shown schematically in (b), the transparent image is light as shown on the left side of the figure when the plate thickness is thin, and the transparent image when the plate thickness is thick is shown on the right side of the figure. It gets darker. The illustrated graph shows an example in which the radioactive waste 100 of an iron-based metal is measured at a tube voltage of 220 kV. Maps created from such relationships are created by accurately testing multiple maps when the tube voltage is changed and a specific plate thickness range (for example, 30 mm-50 mm, 50 mm-100 mm). You can also do it. For example, based on the relationship between the test results, a map can be created as an output as an evaluation of the metal thickness distribution (= weight density distribution) with the data of the tube voltage and the amount of X-ray transmission as the input side.

Then, based on these test results, it is possible to create a calculation system (program) that can be converted into a weight density distribution based on a map created from the tube voltage and the amount of transmission when irradiated with X-rays. Using this calculation system, the weight / density is measured (understood) by converting it into a weight density distribution based on the data obtained from the amount of X-ray transmission detected by the X-ray detection unit 36 of the weight distribution measurement unit 30. Can be done.

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

In addition, based on the total weight of the container 10 previously measured by the weight measuring unit 20, the weight / density data obtained by the weight distribution measuring unit 30 may be assigned the weights of the divided regions A to D. .. Further, since the permeation dose is saturated or cannot be measured at a constant dose due to the difference in the packing density of the radioactive waste 100, several patterns of tube voltages are changed for each of the divided regions A to D to obtain an appropriate permeated dose. By doing so, an accurate weight / density may be calculated.

Further, the method of estimating the weight and density of the radioactive waste 100 from 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 mathematical 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 such a weight distribution measuring unit 30, each divided region is based on the amount of X-ray transmission obtained by irradiating each divided region A to D, which is virtually divided into four containers 10, with X-rays. It is possible to grasp the weight and density inside A to D. Therefore, when the radioactive waste 100 is randomly stored in the container 10 without pretreatment, a difference in filling density occurs in each of the divided regions A to D of the container 10, but the radioactive waste 100 is X-rayed. The weight and density in the four divided regions A to D can be appropriately grasped by measuring the weight distribution based on the amount of transmission obtained by the X-ray detection unit 36 by irradiating with.

(Measurement by radiation measurement unit 50)
FIG. 7 is a perspective view schematically showing an arrangement example of the radiation detector (plastic scintillator 55) and the radiation emitting nuclei species analyzer (Ge semiconductor detector 56) shown in FIG. 8 (a) to 8 (d) 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.

As shown in FIG. 7, the radiation measuring unit 50 in this embodiment measures the radiation amount (counting radiation) with the plastic scintillator 55 for one of the divided regions A to D of the container 10, and the divided regions A to D are used. The Ge semiconductor detector 56 detects the radiation emitting nuclei with respect to the other one of D. This makes it possible to efficiently measure the radiation amount by the plastic scintillator 55 and the radiation emitting nuclei by the Ge semiconductor detector 56.

Hereinafter, the measurement of the radiation dose and the measurement of the radiation emitting nuclide by the radiation measuring unit 50 will be described with reference to FIGS. 8 (a) to 8 (d).

As shown in FIG. 8A, with respect to the container 10 arranged at a predetermined position of the radiation measurement unit 50, in the divided region A, the radiation amount in the divided region A is provided by the plastic scintillator 55 arranged in the vertical direction of the container 10. Is measured. Further, in the divided region C, the Ge semiconductor detector 56 arranged above the container 10 detects the radiation emitting nuclide in the divided region C. When the radiation dose in the divided region A and the detection of the radiation emitting nuclide in the divided region C are performed, the container 10 is sent to the container rotating unit 40, rotated by 90 °, and then returned to the radiation measuring unit 50. Is done.

Next, as shown in FIG. 8B, in the divided region B, the radiation dose in the divided region B is measured by the plastic scintillator 55 arranged in the vertical direction of the container 10. Further, in the divided region D, the Ge semiconductor detector 56 arranged above the container 10 detects the radiation emitting nuclide in the divided region D. When the radiation dose in the divided region B and the detection of the radiation emitting nuclide in the divided region D are performed, the container 10 is sent to the container rotating unit 40, rotated by 90 °, and then returned to the radiation measuring unit 50. Is done.

In this embodiment, since the container 10 is virtually divided into four divided regions A to D, next, as shown in FIG. 8 (c), the measurement of the radiation amount in the divided region C and the divided region are performed. Detection of radiation-emitting nuclides in A is performed. After that, it is rotated by 90 ° as described above, and then, as shown in FIG. 8D, the radiation dose in the divided region D is measured and the radiation emitting nuclide is detected in the divided region B.

In this way, the radiation dose is measured and the radiation emitting nuclide is detected for all of the divided regions A to D, respectively.

(Example of evaluation method)
[Creation of radioactivity concentration conversion coefficient]
For each of the divided regions A to D, create a radioactivity concentration conversion coefficient for evaluating (estimating) the radioactivity concentration (Bq / g) of the radioactive waste 100 from the measurement result (cps) of the radiation amount. .. The radioactivity concentration conversion coefficient is set based on a detailed evaluation based on theoretical calculations such as QAD (Point Attenuation Nuclear Integral Method Analysis Code) for a model assuming a simulated test actual machine scale.

The radioactivity concentration conversion coefficient is obtained as a function of these with the transmission thickness estimated based on the count value of the radiation dose measured for each of the divided regions A to D and the measurement result of the weight / density as the main parameters. The radioactivity concentration conversion coefficient reflects the position, distribution and estimation of the radioactive material attached to the radioactive waste 100 and the decay due to self-absorption in the calculation of the detection efficiency in the radiation count, and is used for each of the divided regions A to D. Can be asked for. It is desirable that this radioactivity concentration conversion coefficient eliminates excessive maintainability as much as possible while ensuring that the probability that the evaluation result is lower than the actual radioactivity concentration is sufficiently low.

As the count value (absolute value) of the radiation dose, 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 coefficient incorporated in the evaluation system.

The validity of the set radioactivity concentration conversion coefficient can be confirmed by a mock test or a simulation test by MCNP (Monte Carlo N-Particle Transport Code) or the like.

Further, the count for each radionuclide is obtained from the radiation count value obtained by the plastic scintillator 55 and the radiation emission nuclide analysis result of the Ge semiconductor detector 56, and the radiation count value is assigned based on the abundance ratio of the radionuclide. It is also possible to evaluate the radioactivity concentration.

[Creation of evaluation model formula]
By detailed evaluation such as MCNP, it is possible to create a safety factor for an evaluation model formula and a clearance judgment reference value having maintainability within a reasonable range. The rational range is a range in which excessive maintainability is excluded 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 in which the input value (cps at the measurement position, g / cm ² ) from the radiation emission nuclei type analyzer (Ge semiconductor detector 56) is input.

The radioactivity concentration level of the radioactive waste 100 is expected to be about 1/10 of the clearance judgment standard value (clearance level), and as the upper limit of the detection limit concentration, for example, Co-, which is estimated to make a large contribution among the nuclides to be evaluated. 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-mentioned radioactivity concentration evaluation device 1, radioactivity is obtained from the radiation count value and the analysis result of the radiation emitting nuclide for each of the divided regions A to D in which the internal space of the container 10 is virtually divided into four in a plan view. It becomes possible to appropriately evaluate the radioactivity concentration of the nuclide to be evaluated contained in the waste. According to such a radioactivity concentration evaluation device 1, even if the radioactive waste 100 is randomly stored in the container 10, the radioactivity concentration of the radioactive waste 100 is accurately measured for each of the plurality of divided regions A to D. can do. Therefore, by randomly storing the radioactive waste 100 in the container 10, it is possible to significantly reduce the time and labor required to store the radioactive waste 100 in the container 10.

Further, in the evaluation of the radioactivity concentration, the radioactivity concentration can be evaluated by allocating the radiation count value based on the abundance ratio of the radionuclide. Further, the radioactivity concentration of the nuclide to be evaluated contained in the radioactive waste 100 can be evaluated for each of the divided regions A to D.

Then, by appropriately evaluating the radioactive concentration of the radioactive waste 100, if the radioactive concentration of the radioactive waste 100 in all the divided regions A to D is equal to or lower than the clearance level, the radioactive in the container 10 is radioactive. The waste 100 can be disposed of and reused in the same manner as general waste. Therefore, the management cost can be reduced.

When the radioactive concentration exceeds the clearance level in a part of the divided regions A to D, the radioactive waste 100 in the divided regions A to D exceeding the clearance level is individually disposed of as low-level radioactive waste 100. Or, it is possible to take appropriate measures such as disposing of the radioactive waste 100 in the container 10 based on the evaluation of the entire radioactive waste 100.

(Other variants)
In the radioactivity concentration evaluation method of the above-described embodiment, an example in which the internal space of the container 10 is virtually divided into four in a plan view has been described, but the number of virtually dividing the internal space of the container 10 is four. Not limited. The number of virtually dividing 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 the density measuring device, and the like.

Further, in the radioactivity concentration evaluation device 1 of the above-described embodiment, each unit 20, 30, 40, 50 is arranged linearly, but the arrangement of each unit 20, 30, 40, 50 is linearly arranged. Not limited to, but not limited to, this embodiment. For example, the weight distribution measurement unit 30 and the radiation measurement unit 50 may be arranged side by side, and the container rotation unit 40 may be arranged between them.

Further, the combination of each configuration in the above-described embodiment is an example, and some configurations may serve as two configurations. For example, the container rotation unit 40 may be provided with the function of the weight measuring unit 20, and these units may be configured as one. Further, although the radioactivity concentration evaluation device 1 of this embodiment has been described with the configuration including the weight measurement unit 20, the weight measurement of the container 10 can also be performed outside the radioactivity concentration evaluation device 1. For example, a known load cell weigh scale can be used for weight measurement. As described above, the combination of each configuration is not limited to the above-described embodiment.

Further, the above-described embodiment shows an example, and various modifications can be made without impairing the gist of the present invention. For example, a container receiving unit (not shown) may be provided in the upstream direction of the weight distribution measuring unit 30, and a container discharging unit (not shown) may be provided in the downstream direction of the radiation measuring unit 50. Not limited to.

(Summary)
According to the above-mentioned radioactivity concentration evaluation method, the radioactivity randomly stored in the container 10 is measured by measuring the weight or density distribution for each of the divided regions A to D in which the internal space of the container 10 is virtually divided. It is possible to appropriately grasp the weight and density of the waste 100 and appropriately evaluate the radioactivity concentration. That is, it is expressed in terms of radioactivity per unit weight (becquerel / gram: Bq / g), and is emitted from the measured radiation using a clearance measuring device approved by the government as a method for measuring and evaluating the radioactivity concentration. It is possible to evaluate the ability and divide by the measured weight to evaluate the radioactivity concentration (Bq / g).
Therefore, by randomly storing the radioactive waste 100 in the container 10, the pretreatment work such as cutting and evenly spreading the radioactive waste 100 can be significantly reduced, and the work of storing the radioactive waste 100 in the container 10 can be significantly reduced. It is possible to significantly reduce the time and labor required for this.

Then, from the radiation dose and the composition of the nuclei in each of the divided regions A to D measured by the radiation measuring unit 50, the radioactivity concentration (Bq / g) of the radioactive waste 100 randomly stored inside the container 10 is the clearance. It is possible to appropriately evaluate whether or not a predetermined set value for the level (for example, about 1/10 of the clearance level) is exceeded. As a result of this evaluation, if the radioactive waste 100 is at a clearance level or less that does not need to be treated as a radioactive substance for safety, it can be appropriately disposed of as general waste, and management costs can be reduced. ..

1 Radioactivity concentration evaluation device 10 Container 15 Virtual line 20 Weight measurement unit 25 Weight measurement device 30 Weight distribution measurement unit 35 X-ray irradiation unit (density measuring device)
36 X-ray detector (density measuring instrument)
37 Shielding wall 40 Container rotation unit 45 Relocation device 50 Radiation measurement unit 55 Plastic scintillator (radiation dose measuring instrument)
56 Ge semiconductor detector (radiation emitting nuclide analyzer)
57 Shielding wall 60 Control device 61 Data processing unit 100 Radioactive waste A to D division area

Claims (8)

It is a method for evaluating the radioactivity concentration of radioactive waste.
Put the radioactive waste in a container and put it in a container.
The internal space of the container is virtually divided into a plurality of divided areas.
Radiation is applied to each of the divided regions, and the weight or density of the radioactive waste inside is measured from the amount of the radiation transmitted.
The radiation emitted from the radioactive waste was counted and the radiation nuclides were analyzed for each divided region.
The radioactivity concentration of the nuclide to be evaluated contained in the radioactive waste is evaluated from the count value of the radiation, the analysis result of the radiation emitting nuclide, and the weight or density.
A method for evaluating a radioactivity concentration, which is characterized by the fact that. The radiation emitted from the radioactive waste is counted by a radiation detector, and the radiation is counted.
The radiation-emitting nuclides emitted from the radioactive waste are analyzed with a radiation-emitting nuclide analyzer.
Obtain the count for each radionuclide from the radiation count value obtained by the radiation detector and the radiation emission nuclide analysis result of the radionuclide analyzer, and allocate the radiation count value based on the abundance ratio of the radionuclide to emit radiation. Evaluate the ability,
The radioactivity concentration evaluation method according to claim 1. The radioactivity of the evaluation target nuclide contained in the radioactive waste is evaluated for each of the divided regions based on the radiation count value and the analysis result of the radiation emitting nuclide.
The radioactivity concentration evaluation method according to claim 2. From the radiation count value measured for each divided region, the position, distribution and radioactivity of the radioactive substance adhering to the radioactive waste in the container are estimated.
The radioactivity concentration evaluation method according to claim 2 or 3. Based on the weight measurement result for each divided region of the radioactive waste, the attenuation due to the 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 the counting of the radiation. I did,
The radioactivity concentration evaluation method according to claim 4. The count value of the radiation, the detection value of the radiation emitting nuclei species analyzer, the position and distribution of the radioactive substance attached to the radioactive waste in the container, the estimation of the radioactivity, and the weight or density of each divided region. From the measurement results, the decay is reflected in the calculation of the detection efficiency in the radiation count, and the radioactivity concentration conversion coefficient is set for each divided region.
The radioactivity concentration evaluation method according to claim 5. The count value of the radiation counted by the radiation detector, the analysis result of the radiation emitting nuclide analyzed by the radiation emitting nuclide analyzer, and the measurement result of the weight or density for each divided region are combined.
The radioactivity concentration for each divided region is evaluated by the radioactivity concentration conversion coefficient.
The radioactivity concentration evaluation method according to claim 6. The measurement of the weight or density distribution of the radioactive waste in the container is made to reflect the absorption of the radiation by the radioactive waste.
The radioactivity concentration evaluation method according to any one of claims 1 to 7.

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