JP4869192B2 - Radioactivity measurement method for radioactive waste - Google Patents

Description

  The present invention relates to a method for measuring radioactivity of radioactive waste, and in particular, radioactivity suitable for nondestructively measuring radioactivity intensity in a radioactive waste storage container (hereinafter simply referred to as storage container) such as a drum can. The present invention relates to a method for measuring radioactivity of waste.

  Japanese Patent Publication No. 7-11573 discloses a radioactivity measurement method for measuring the radiation emitted from a storage container filled with radioactive waste to determine the radioactivity intensity in the storage container.

  This conventional radioactivity measurement method will be described in detail. Non-scattering that is released from the radionuclide contained in the radioactive waste inside the storage container and transmitted through the storage container to the outside by the radiation detector placed outside the storage container filled with radioactive waste A line (hereinafter referred to as a direct line) and a scattered ray that has once scattered inside the storage container and then passed through the storage container and reached the outside are detected. The respective intensities of the detected direct ray and scattered ray are obtained, and the ratio of the intensity of the scattered ray as the spectral index and the intensity of the direct ray is obtained. Based on the obtained spectral index, the average density of the radioactive waste filled inside is determined in a certain cross section of the storage container. Furthermore, the radioactivity in the cross section is obtained based on the average density and the direct line count rate. By adding the radioactivity in all cross sections in the axial direction, the total radioactivity in the storage container is determined.

  Japanese Patent Application Laid-Open No. 6-258896 discloses that when measuring the radioactivity in a storage container filled with radioactive waste, the storage container is moved in one linear direction in the horizontal direction and in a direction perpendicular to the linear direction. Furthermore, it is described that it is rotated in a horizontal plane. Furthermore, the configuration of the device that enables their movement and rotation is described.

Japanese Examined Patent Publication No. 7-11573 Japanese Patent Application Laid-Open No. 6-258896

  The radioactivity measurement method described in Japanese Examined Patent Publication No. 7-11573 measures each of direct rays and scattered rays, obtains an average density using a spectrum index obtained based on these measured values, and calculates the average Since the radioactivity in the storage container is obtained by using the density and the direct line count rate, the time for measuring the radioactivity can be shortened.

  In such radioactivity measurement, further improvement in radioactivity measurement accuracy is desired even when the radioactivity intensity in the storage container is strong.

  An object of the present invention is to provide a radioactive waste radioactivity measurement method capable of further improving the radioactivity measurement accuracy.

  A feature of the present invention that achieves the above-described object is that a rotary table on which a storage container containing radioactive waste is placed is rotated, and radiation emitted from the rotating storage container is detected by a first radiation detector. The radiation counting rate is obtained, the radiation emitted from the rotating storage container is detected by the second radiation detector, and the radiation is detected by the second radiation detector, and the storage container is rotated based on the radiation detection rate. The rotational speed of the table is controlled, and the radioactivity intensity of the storage container is obtained based on the radiation detection signal from the second radiation detector.

  Since the present invention controls the rotation speed of the rotary table on which the storage container is placed based on the radiation count rate obtained by the first radiation detector, the counting loss of the output of the second radiation detector is significantly reduced. For this reason, even if the measurement position of a radiation changes, the detection sensitivity of a radiation can be made substantially the same, and the precision of the radioactivity measurement of a storage container can be improved further. In particular, even when the concentration of the radionuclide present in the storage container is high, the count loss of the output of the second radiation detector is significantly reduced.

  The above-mentioned purpose is to rotate a rotary table with a storage container containing radioactive waste, detect the radiation emitted from the rotating storage container with a radiation detector, and the pulse height analyzer will detect the radiation at the time of radiation detection. The radiation detector dead time information is obtained based on the output of the detector, and at the time of radiation detection by the radiation detector, the rotational speed of the rotary table on which the storage container is placed is controlled based on the dead time information. This can also be achieved by determining the radioactivity intensity of the storage container based on the output of.

  The rotation speed of the rotary table on which the storage container is placed is controlled using the radiation detector dead time information obtained by the pulse height analyzer based on the output of the radiation detector. Is significantly reduced. For this reason, even if the measurement position of a radiation changes, the detection sensitivity of a radiation can be made substantially the same, and the precision of the radioactivity measurement of a storage container can be improved further.

  According to the present invention, the measurement accuracy of the radioactivity of the storage container can be further improved.

  As a result of examining the radioactivity measurement method described in Japanese Patent Publication No. 7-11573, the inventors have newly found that the detection sensitivity differs depending on the measurement position of the storage container by the radiation detector arranged outside. It was. That is, the inventors have found a phenomenon that the radiation detection sensitivity differs when radiation is detected by the radiation detector at different positions in the circumferential direction and the axial direction of the storage container. The cause of this phenomenon is that the concentration of radionuclide contained in the radioactive waste filled in the storage container is high, resulting in a dead time for processing the pulse of the radiation detection signal in the radiation detector. . The inventors have found that the fact that this dead time changes at the measurement position of radioactivity, i.e., the position where the radiation detector faces on the outer surface of the storage container, causes the radiation detection sensitivity to change depending on the measurement position. Found out. The dead time changes when the radioactivity measurement position changes because the radioactivity concentration in the storage container is non-uniform. For example, when the spot-like radionuclide is localized in the outer peripheral portion of the storage container, the change in dead time appears remarkably. In other words, when the distance between the localized radionuclide in the storage container and the radiation detector is reduced, the counting rate at the radiation detector is increased, so that the dead time is increased. The present invention has been made based on the new findings obtained by the above studies.

  Examples of the present invention obtained as described above will be described below.

  A radioactivity measurement method for radioactive waste which is a preferred embodiment of the present invention will be described with reference to FIGS. First, the radioactive waste radioactivity measurement apparatus used in the radioactivity measurement method of the present embodiment will be described. The radioactivity measuring device 1 includes radiation detectors 2 and 4, collimators 3 and 5, a storage container moving device 6, a drive control device 14, a pulse height analyzer 15, a photoelectric peak calculator 16, a spectrum index calculator 17, and a radioactivity An arithmetic device 18 is provided. The radioactivity measurement apparatus 1 is installed in a radiation measurement room (not shown) surrounded by a ceiling composed of a radiation shielding wall and a radiation shielding body.

  The storage container moving device 6 includes a moving carriage 7, a lifting platform 8, a rotary table 9, a first driving device 11, a second driving device 12, and a third driving device 13. The movable carriage 7 is movably installed on a pair of guide rails 10 installed on the floor surface of the radiation measurement room. The movable carriage 7 is moved along the guide rail 10 in one horizontal direction in the horizontal direction (L direction shown in FIG. 1) by the driving of the first driving device 11. The support member 20 is installed vertically on the upper surface of the movable carriage 7. The elevator 8 is attached to the support member 20 so as to be movable in the vertical direction, and is moved in the vertical direction (direction perpendicular to the upper surface of the movable carriage 7) (H direction shown in FIG. 2) by the drive of the second driving device 12. The The turntable 9 is rotatably attached to the lift 8 and is rotated in the R direction (see FIG. 1) by the third driving device 13. The rotary table 9 supports a storage container (hereinafter referred to as a subject) 21 filled with radioactive waste during radioactivity measurement. The drive control device 14 includes a moving carriage control device 14 </ b> A that controls the first drive device 11, an elevator control device 14 </ b> B that controls the second drive device 12, and a rotary table control device 14 </ b> C that controls the third drive device 13.

For example, a Ge semiconductor detector is used as the radiation detector 2. The collimator 3 is disposed on the front surface of the radiation detector 2, that is, on the storage container moving device 6 side. The radiation detector 4 is disposed at a position facing the radiation detector 2 with the storage container moving device 6 interposed therebetween. For example, a plastic scintillation detector that can cope with a high count rate is used. The collimator 5 is disposed on the front surface of the radiation detector 4, that is, on the storage container moving device 6 side. The radiation detectors 2 and 4 and the collimators 3 and 5 are installed on the floor surface. The collimator 3 includes a vertical collimator 3B provided so as to be able to measure only radiation emitted from a radionuclide in one cross section 26 having a width Δh in the axial direction of the subject 21, and an arbitrary one in the cross section 26. It has a horizontal collimator 3A for correcting the geometric efficiency for position 22. Collimator 5 likewise has a horizontal collimator 5A and vertical collimator 5B.

  The radiation detector 2 is connected to the wave height analyzer 15. The photoelectric peak calculation device 16 is connected to the wave height analysis device 15, and the spectrum index calculation device 17 is connected to the photoelectric peak calculation device 16. The radioactivity calculation device 18 is connected to the photoelectric peak calculation device 16 and the spectrum index calculation device 17. The display device 19 is connected to the radioactivity calculation device 18. The radiation detector 4 is connected to the rotary table control device 14C.

  The scanning range S of the subject 21 determined by the relative positional relationship among the radiation detector 2, the horizontal collimator 3A, the vertical collimator 3B, and the subject 21 is the angle 25 of the opening of the horizontal collimator 3A and the radiation detector 2 and the subject. It is determined by the distance of the specimen 21. The geometric efficiency with respect to the direct line 23 (see FIG. 1) in the scanning range S considering the rotation measurement of the subject 21 is very dependent on the position of the radionuclide in the radial direction of the subject 21, as shown in FIG. It is chosen not to. If the change range of the geometric efficiency shown in FIG. 3 becomes large, the quantitative accuracy of the radionuclide radioactivity concentration deteriorates. Therefore, the change range of the geometric efficiency depends on the target radioactivity concentration determination accuracy. Is determined. The geometric efficiency shown in FIG. 3 is realized by changing the moving speed of the subject (storage container) 21 along the guide rail 10 as shown in FIG. This moving speed is a function of the rotational speed of the subject 21, the radial position where the radiation detector 2 expects the center of the subject 21, and the opening angle 25, and is stored in a storage device (not shown) of the drive control device 14. Stored in advance.

  Since the concentration of the radionuclide contained in the subject 21 to be measured is high, the radiation detector 2 causes a dead time when performing the pulse counting process of the radiation detection signal. This dead time is because the radionuclide concentration is high, the intensity of the radiation entering the radiation detector 2 becomes high, and the processing of the pulse of the radiation signal generated in the radiation detector 2 by the radiation cannot catch up, This is the amount corresponding to the time during which the pulses of the radiation detection signal are counted down. That is, the dead time is a time when the radiation detector 2 is not functioning substantially. The long dead time substantially corresponds to low radiation detection sensitivity. The length of the dead time greatly varies depending on the measurement position of the radiation detector 2 when the radionuclide concentration distribution in the subject 21 is not uniform. Therefore, in order to make the pulse counting time at an arbitrary measurement position of the subject 21 substantially constant, it is necessary to change the rotational speed of the subject 21 according to the amount of dead time described above. As shown in FIG. 5, when the amount of dead time is large, the rotational speed of the subject 21, that is, the rotary table 9, is slower than the rotational speed when the dead time amount can be regarded as zero.

The radioactivity measurement method of a present Example is demonstrated. A subject 21 filled with radioactive waste is carried into the radiation measurement chamber, placed on the turntable 9, and attached to the turntable 9. Operator can be the operation command output by operating a button on the operation panel (not shown) moving carriage control device 14A, is input to the lifting table control unit 14B and the rotary table controller 14C. Moving carriage control device 14A, lifting table control unit 14B and the rotary table controller 14C includes a first driving unit 11, the second driving device 12 and the third drive unit 13, with respect to the subject 21 is the radiation detector 2 Drive to be positioned at the measurement start position.
For this reason, the cross section 26 having the width Δh located at the lowest position is aligned with the position in the height direction of the radiation detector 2, and the measurement start point in the circumferential direction of the subject 21 is opposed to the radiation detector 2. As the moving carriage 7 moves, the subject 21 is positioned at the measurement start point in the L direction.

Thereafter, radiation measurement of the subject 21 is started. The radiation detector 2 has a width ΔL for starting measurement in the L direction first in one cross section 26 positioned at the lowest position (the lowest position of the scanning range S determined in advance to satisfy FIG. 3) in the L direction. In the state of being opposed, the operator outputs a radioactivity measurement start command from the operation panel to the rotary table control device 14C. The rotary table control device 14C drives the third drive device 13 to rotate the rotary table 9, and rotates the subject 21 by, for example, 365 °. The radiation detector 2 detects the radiation emitted from the subject 21 during its rotation. The rotary table control device 14C receives an output of a third encoder (not shown) that is provided in the third driving device 13 and detects a circumferential position, and rotates when the subject 21 is rotated 365 °. The rotation of the table 9 is stopped. Thereby, the radiation measurement in one cross section 26 in the initial state is completed. The moving carriage control device 14A that inputs the output of the third encoder drives the first driving device 11 to move the moving carriage 7 after the subject 21 is rotated by 365 °, and moves the subject 21 by the width ΔL to L. Move in the direction. The output of the first encoder that is provided in the first drive device 11 and detects the position in the L direction is input to the movable carriage control device 14A and the rotary table control device 14C. The moving carriage control device 14A stops the moving carriage 7 when detecting that the movement of the width ΔL of the subject 21 is completed based on the output of the first encoder. After stopping the movable carriage 7, the rotary table control device 14C drives the third driving device 13 to rotate the rotary table 9, and rotates the subject 21 again by 365 °. In this way, the movement of the movable carriage 7 for each width ΔL and the rotation of the rotary table 9 are repeated for one transverse section 26, and radiation measurement by the radiation detector 2 is performed each time. When the radiation detection at one of the cross sections 26 by the movement of the width ΔL is completed (when the radiation detection to the uppermost position of the scanning range S determined in advance to satisfy FIG. 3 is completed). , lifting table control device 14B for receiving the output of the first encoder, the second driving unit 12 is driven to move the elevation frame 8 downward, is moved downward to the subject 21 by the width Delta] h. The second lifting table control device 14B for receiving the output of the encoder for detecting the position in the vertical direction is provided on the second drive apparatus 12, the second driving device 12 when it detects the movement of the width Δh of the elevation frame 8 Stop driving. At this time, the other cross section 26 faces the radiation detector 2. The rotary table control device 14C that inputs the output of the second encoder drives the third drive device 13 to rotate the subject 21 by 365 ° after the downward movement of the lifting platform 8 is stopped. In this way, the radiation measurement by the radiation detector 2 on the other cross section 26 is started. The movement and rotation of the subject 21 for each width ΔL as described above are repeated with respect to the other cross section 26, and the radiation detection by the radiation detector 2 is performed. Further, the radiation detection by the radiation detector 2 is continued until the radiation measurement for the uppermost width Δh of the subject 21 is completed.

The scanning range h in the axial direction of the subject 21 at the time of performing radiation measurement over the entire length in the axial direction of the subject 21 by moving the lift 8 in the vertical direction by a width Δh is the opening angle 27 of the vertical collimator 3B. Considering this, the region includes the entire axial direction of the subject 21 (see FIG. 6). By performing radiation measurement on the scanning range h, the radioactivity distribution in the axial direction of the subject 21 can be obtained. In FIG. 6, C shows a state in which the radiation detector 2 is positioned below the lower end of the subject 21 due to the movement of the lifting platform 8, and D shows the upper end of the subject 21 due to the movement of the lifting platform 8. The state located above is shown.

This embodiment, as described above, to move between the width ΔL of the object 21 by moving carriage control device 14A inputs the output of the third encoder, lifting table control device 14B is an output of the first encoder By inputting, the width 21h of the subject 21 is moved. However, by inputting the moving carriage movement command output from the operation panel by the operator's operation to the moving carriage control device 14A, the subject 21 is moved by the width ΔL, and the lifting / lowering output from the operation panel by the operator's operation is performed. The movement of the subject 21 by the width Δh may be performed by inputting a table movement command to the lifting platform control device 14B.

  In the present embodiment, the amount of dead time of the radiation detector 2 is a radiation detection signal (direct line 23 and scattered radiation 24) detected by the radiation detector 4 facing the radiation detector 2 and the subject 21 therebetween. The radiation count rate obtained based on the radiation detection signal for each is used. The radiation measurement for obtaining the radiation count rate is performed by moving and rotating the subject 21 by the storage container moving device 6 before the radiation detection by the radiation detector 2. Such radiation measurement by the radiation detector 4 is performed more roughly than radiation measurement by the radiation detector 2. This radiation count rate is a state quantity that represents the amount of dead time, and is input to the rotary table control device 14C and stored in the storage device of the drive control device 14.

  In the radiation measurement by the radiation detector 2 described above, the rotational speed of the rotary table 9 is controlled by the rotary table control device 14C as follows. The rotary table control device 14C detects the position of the subject 21 in the circumferential direction facing the radiation detector 2 based on the output of the third encoder, and detects the radiation of the subject 21 based on the output of the first encoder. The positions in the L direction at which the devices 2 are opposed to each other are obtained, and the radiation count rates obtained by the radiation detector 4 corresponding to the positions are read out from the storage device. At this time, since the radiation detector 4 and the radiation detector 2 are opposed to each other with the subject 21 interposed therebetween, information on a position in the circumferential direction rotated by 180 ° is read. Further, the rotation table control device 14C gives a rotation control command representing the rotation speed obtained based on the radiation count rate and the characteristic information of FIG. 5 stored in the storage device of the drive control device 14 to the third drive device 13. To control the rotational speed of the rotary table 9. In this way, the rotation speed of the subject 21 is controlled during radiation measurement by the radiation detector 2.

  In this embodiment, the rotation speed of the rotary table 9 is controlled based on the radiation count rate obtained by the radiation detector 4, but the rotation of the rotary table 9 is controlled based on the radiation count rate obtained by the radiation detector 2. It is also possible to control the speed. That is, if the radiation from the subject 21 is measured at a rotation position of 360 ° + 180 ° using the radiation detector 2, the rotation control of the rotary table 9 in one pass becomes possible. For example, the radiation count rate measured at the position A in the circumferential direction by the radiation detector 4 becomes the count rate at the radiation detector 2 when the subject 21 is further rotated 180 °.

  In this embodiment, since the movable table 7 is moved in the L direction and the turntable 9 is rotated, the radiation detector 2 passes through the subject 21 radiated from the radionuclide present at the position 22, for example. Further, the direct ray (non-scattered ray) 23 and the scattered ray 24 that is scattered by the radioactive waste in the subject 21 and transmitted through the subject 21 are detected. In FIG. 1, the radiation detector 2 at the position B represents a state in which the measurement position is shifted from the radiation detector 2 at the position A due to the movement of the movable carriage 7 in the L direction.

  The output from the radiation detector 2 that has detected the direct line 23 or the scattered radiation 24 is input to the wave height analyzer 15. The pulse height analyzer 15 obtains an energy spectrum caused by the direct line 23 and the scattered line 24. The peak value distribution of this energy spectrum changes depending on the density of the radioactive waste contained in the subject 21. Generally, when the density increases, the intensity of the direct line 23 decreases, and the relative value of the intensity of the scattered radiation 24 with respect to the intensity of the direct line 23 increases. Information on the energy spectrum obtained by the pulse height analyzer 15 is input to the photoelectric peak arithmetic device 16. The photoelectric peak calculation device 16 obtains the scattered ray intensity C and the direct ray intensity P using the information of the energy spectrum. The scattered ray intensity C and direct ray intensity P obtained by the photoelectric peak calculation device 16 are input to the spectrum index calculation device 17. The spectrum index calculation device 17 obtains the ratio C / P of the scattered radiation intensity C and the direct line intensity P, which is a spectrum index, for each radionuclide based on the intensity. The radioactivity calculation unit 18 is based on the spectrum index C / P for each radionuclide output from the spectrum index calculation unit 17 and the scattered radiation intensity C and direct line intensity P output from the photoelectric peak calculation unit 16. Then, the attenuation of the direct line 23 in the subject 21 is corrected, and the radioactivity intensity of the radionuclide is calculated for each cross section 26 in the subject 21. Further, the radioactivity calculation device 18 calculates the total radioactivity intensity over the entire length of the subject 21 in the axial direction by adding the radioactivity intensities of these cross sections 26. Information on each radioactivity intensity obtained by the radioactivity calculation device 18 is output from the radioactivity calculation device 18 to the display device 19 and displayed on the display device 19. The radioactivity intensity is printed on recording paper by a printer (not shown).

  An example of an energy spectrum obtained based on the output of the radiation detector 2 when two types of radionuclides of Co-60 and Cs-137 exist in the subject 21 and the radioactivity distributions of the two are the same. Is shown in FIG. Since Co-60 emits two types of radiation energy and is higher than the radiation energy emitted by Cs-137, the spectral index for Co-60 obtained in this measurement example is attributed to the radiation of Co-60. The ratio C1 / (P11 + P12) of the scattered ray intensity C1 and the direct ray intensity (P11 + P12) is obtained.

  FIG. 8 shows an example of characteristics indicating the relationship between the spectral index and the radiation attenuation rate in the subject 21 when the radioactivity distributions of Co-60 and Cs-137 are the same. This characteristic can be easily obtained by a calibration test. Therefore, if the spectrum index can be obtained from the measured energy spectrum shown in FIG. 7, the attenuation ratio in the subject 21 of each radiation emitted from Co-60 and Cs-137 is calculated from the characteristics shown in FIG. Can do. For this reason, the radioactivity intensity | strength in the subject 21 of those radionuclides can be calculated | required accurately. The scattered radiation intensity C <b> 1 shown in FIG. 7 is also affected by scattered radiation once the direct line 23 is scattered inside each of the collimators 3 and 4 and the radiation detector 2. Therefore, each characteristic shown in FIG. 8 shows a value obtained by subtracting the spectrum index when the subject 21 is not present from the spectrum index obtained based on the measured energy spectrum shown in FIG. 7 as the spectrum index C / P.

  In this embodiment, since the rotation speed of the rotary table 9 is controlled using the radiation count rate output from the radiation detector 4, the pulse counting time at an arbitrary measurement position of the subject 1 is made substantially constant. can do. When the radiation count rate output from the radiation detector 4 is low, the rotation speed of the rotary table 9 is increased, and when the radiation count rate is high, the rotation speed is decreased. For this reason, even when the concentration of the radionuclide in the subject 21 is high and the radiation count rate is high, that is, the dead time of the radiation detector 2 is increased, the radiation detection signal output from the radiation detector 2 is output. Can be significantly reduced. The pulses of the radiation detection signal output from the radiation detector 2 can be substantially all measured, and the radiation detection sensitivity becomes substantially the same even if the measurement position of the radiation detector 2 changes. For this reason, the accuracy of the radioactivity measurement of the subject 21 can be further improved.

The radioactivity measurement method for radioactive waste according to embodiment 2, which is another embodiment of the present invention, will be described with reference to FIG. In this embodiment, the radiation detector 2 is disposed at a position sufficiently away from the subject 21, and the geometric efficiency in the absence of the collimator 3 almost depends on the position of the radionuclide in the subject 21. It is an example of the radioactivity measurement when not. Also in this embodiment, the radioactivity measuring apparatus 1 is used. However, the radiation detector 2 and the collimator 3, Ri Contact away from the subject 21 than in Example 1, the opening angle 25 of the horizontal collimator 3 A is a case very small. In this embodiment, the scanning range S of the radiation detector 2 for moving the moving carriage 7 in the L direction, in consideration of the horizontal collimator 3 A of the opening angle 25, including one entire cross-section 26 of the subject 21 Become a range.
In FIG. 9, E indicates a state in which the radiation detector 2 is positioned outside the outer periphery of the subject 21 in the horizontal direction by the movement of the movable carriage 7, and F indicates that the radiation detector 2 is E by the movement of the movable carriage 7. The state which is located outside the outer periphery of the subject 21 on the opposite side of the state by 180 ° is shown.

  In the present embodiment, similarly to the first embodiment, the rotary table control device 14C controls the third drive device 13 using the radiation count rate obtained by the radiation detector 4, and the rotational speed of the rotary table 9, that is, The rotational speed of the subject 21 is adjusted.

  In the present embodiment, the effects produced in the first embodiment can be obtained.

  A radioactivity measurement method for radioactive waste according to embodiment 3, which is another embodiment of the present invention, will be described with reference to FIG. In this embodiment, the radiation measurement at one cross section 26 is not performed by moving the movable carriage 7 in the L direction as in the first embodiment, but the orientations of the radiation detector 2 and the radiation detector 4 in the horizontal direction are It is done by changing each. In the radioactivity measuring apparatus 1A used in the present embodiment, the moving carriage 7, the first driving apparatus 11, and the moving carriage control apparatus 14A are deleted from the radioactivity measuring apparatus 1, and the radiation detector 2 is rotated in a horizontal plane. A rotating device (not shown) and a second rotating device (not shown) for rotating the radiation detector 4 in a horizontal plane are added. The first rotation device is controlled by a first rotation control device (not shown), and the second rotation device is controlled by a first rotation control device (not shown). The radioactivity measuring apparatus 1A has a support base (not shown) installed on the floor instead of the movable carriage 7, and the rotary table 9 and the support member 20 are installed on the support base. The radiation detector 2 and the collimator 3 are rotated in the range of the rotation angle θ in the horizontal plane with respect to the axis of the opening (the axis of the radiation detector 2) formed in the collimator 3 and through which the radiation passes. Such rotation is performed by driving a first rotating device (not shown). Specifically, the radiation detector 2 and the collimator 3 each have a rotation angle θ / 2 on both sides of the straight line connecting the axis of the opening of the collimator 3 and the axis of the subject 21 in the horizontal plane. Rotated in range. The radiation detector 4 and the collimator 5 are rotated in the range of the rotation angle θ within the horizontal plane with respect to the axial center of the opening formed in the collimator 5 and through which the radiation passes (the axial center of the radiation detector 4). Such rotation is performed by driving the second rotating device. Specifically, the radiation detector 4 and the collimator 5 have a rotation angle θ / 2 on both sides of the straight line connecting the axis of the opening of the collimator 5 and the axis of the subject 21 in the horizontal direction. Rotated in range. These rotation angles θ depend on the opening angles of the horizontal collimators 3A and 5A. Even in this case, the geometric efficiency considering that the subject 21 rotates in the R direction can be made the same as the characteristic shown in FIG. 3 by optimizing the rotation angle θ. In the present embodiment, a case where the straight line connecting the axis of the collimator 3 and the axis of the subject 21 and the line connecting the axis of the collimator 5 and the axis of the subject 21 is 90 ° C. is shown. .

The radioactivity measurement method of the present embodiment will be specifically described. A subject 21 filled with radioactive waste is attached to the turntable 9. Operator control panel (not shown) on the the operation command output by operating the button of the first rotary control device, the second rotation control device, are input to the lifting table control unit 14B and the rotary table controller 14C The First rotation control device, the second rotation control device, lifting table control unit 14B and the rotary table controller 14C includes a first rotating device, a second rotary device, the second driving device 12 and the third driving device 13, the The specimen 21 is driven so as to be positioned at the measurement start position with respect to the radiation detector 2. For this reason, the cross section 26 having the width Δh located at the lowermost position is aligned with the position in the height direction of the radiation detector 2, and the measurement start point in the circumferential direction of the subject 21 is opposed to the radiation detectors 2, 4. The Radiation is detected at the measurement start point of the subject 21 in the θ direction by the rotation of the first rotating table (not shown) by the first rotating device and the rotation of the second rotating table (not shown) by the second rotating device. Devices 2 and 4 are positioned. The radiation detector 2 is installed on the first point base, and the radiation detector 4 is installed on the second turntable.

Thereafter, radiation measurement of the subject 21 is started. Radiation detection is performed for a width Δθ at which measurement is first started in the θ direction at one cross section 26 located at a position −θ / 2 (the smallest position of the scanning range θ determined in advance to satisfy FIG. 3). The operator outputs a radioactivity measurement start command from the operation panel to the rotary table control device 14 </ b> C in a state of facing the device 2. The rotary table control device 14C drives the third drive device 13 to rotate the rotary table 9, and rotates the subject 21 by, for example, 365 °. The radiation detector 2 detects the radiation emitted from the subject 21 during its rotation. The rotary table control device 14C receives an output of a third encoder (not shown) that is provided in the third driving device 13 and detects a circumferential position, and rotates when the subject 21 is rotated 365 °. The rotation of the table 9 is stopped. Thereby, the radiation measurement in one cross section 26 in the initial state is completed. The first rotation control device and the second rotation control device that input the output of the third encoder drive the first rotation device and the second rotation device after the subject 21 is rotated by 365 °, and the first rotation carriage and The second rotating carriage is rotated, and the subject 21 is rotated in the θ direction by Δθ. An output of a first rotary encoder (not shown) that is provided in the first rotating device and detects the position of the radiation detector 2 in the θ direction is input to the first rotation control device. An output of a second rotary encoder (not shown) that is provided in the second rotating device and detects the position of the radiation detector 4 in the θ direction is input to the second rotation control device. When the first rotation control device and the second rotation control device detect that the movement of the width Δθ of the subject 21 is completed based on the outputs of the first rotation encoder and the second rotation encoder, the first rotation carriage and the second rotation control device The rotation of the two-turn carriage is stopped. After the rotation of the first rotating carriage and the second rotating carriage is stopped, the rotary table control device 14C drives the third driving device 13 to rotate the rotary table 9, and rotates the subject 21 again by 365 °. In this way, the rotation of the first and second rotary carriages for each width Δθ and the rotation of the rotary table 9 are repeated for one transverse section 26, and each time radiation measurement by the radiation detectors 2 and 4 is performed. To be implemented. Radiation up to the smallest position (+ θ / 2 position) of the scanning range θ determined in advance so as to satisfy FIG. 3 when the radiation detection at that one cross section 26 is completed by the rotation of the width Δθ. when the detection is completed), lifting table control device 14B for inputting the outputs of the first rotary encoder and the second rotary encoder, it moves the elevation frame 8 by driving the second drive unit 12 downward, the subject 21 is moved downward by a width Δh. The second lifting table control device 14B for receiving the output of the encoder for detecting the position in the vertical direction is provided on the second drive apparatus 12, the second driving device 12 when it detects the movement of the width Δh of the elevation frame 8 Stop driving. At this time, the other cross section 26 faces the radiation detector 2. The rotary table control device 14C that inputs the output of the second encoder drives the third drive device 13 to rotate the subject 21 by 365 ° after the downward movement of the lifting platform 8 is stopped.
In this way, the radiation measurement by the radiation detector 2 on the other cross section 26 is started. The rotation of the radiation detectors 2 and 4 and the rotation of the subject 21 as described above are repeated for the other cross section 26 for each width Δθ, and the radiation detection by the radiation detectors 2 and 4 is performed. . Further, the radiation detection by the radiation detector 2 is continued until the radiation measurement for the uppermost width Δh of the subject 21 is completed.

The scanning range h in the axial direction of the subject 21 at the time of performing radiation measurement over the entire length in the axial direction of the subject 21 by moving the lift 8 in the vertical direction by a width Δh is the opening angle 27 of the vertical collimator 3B. Considering this, the region includes the entire axial direction of the subject 21 (see FIG. 6). By performing radiation measurement on the scanning range h, the radioactivity distribution in the axial direction of the subject 21 can be obtained. In FIG. 6, C shows a state in which the radiation detector 2 is positioned below the lower end of the subject 21 due to the movement of the lifting platform 8, and D shows the upper end of the subject 21 due to the movement of the lifting platform 8. The state located above is shown.

  In this embodiment, as the dead time amount of the radiation detector 2, a straight line connecting the axis of the collimator 3 and the axis of the subject 21, and a straight line connecting the axis of the collimator 5 and the axis of the subject 21 are used. The radiation count rate obtained based on the radiation detection signal detected by the radiation detector 4 installed at a position of 90 ° C. is used. In the radiation measurement for obtaining the radiation count rate, the radiation detector 2 and the radiation detector 4 are rotated by the first rotating device and the second rotating device before the radiation detection by the radiation detector 2, and the rotary table is rotated. 9 is performed by rotating the subject 21. Such radiation measurement by the radiation detector 4 is performed more roughly than radiation measurement by the radiation detector 2. This radiation count rate is a state quantity that represents the amount of dead time, and is input to the rotary table control device 14C and stored in the storage device of the drive control device 14.

  In the radiation measurement by the radiation detector 2 described above, the rotational speed of the rotary table 9 is controlled by the rotary table control device 14C as follows. The rotary table control device 14C determines the position of the subject 21 in the circumferential direction facing the radiation detector 2 based on the output of the third encoder, and the radiation of the subject 21 based on the output of the first rotary encoder. The positions in the circumferential (θ) direction where the detector 2 is opposed are obtained, and the radiation count rates obtained by the radiation detector 4 corresponding to both positions are read out from the storage device. At this time, since the radiation detector 4 and the radiation detector 2 are installed at a position of 90 ° with respect to the subject 21, information on the position where the circumferential position of the subject 21 is rotated by 90 ° is read. Further, the rotation table control device 14C gives a rotation control command representing the rotation speed obtained based on the radiation count rate and the characteristic information of FIG. 5 stored in the storage device of the drive control device 14 to the third drive device 13. To control the rotational speed of the rotary table 9. In this way, the rotation speed of the subject 21 is controlled during radiation measurement by the radiation detector 2.

  In this embodiment, the radiation detector 4 provided for predicting the amount of dead time in the radiation detector 2 is synchronized with the rotation angle of the radiation detector 2 rotated in the horizontal plane by the first rotating device. In the horizontal plane by the second rotating device. As described above, since the radiation detectors 2 and 4 are rotated, it is not necessary to move the subject 21 in the L direction for each width ΔL in the first embodiment.

  In the present embodiment, the rotation speed of the rotating table 9, that is, the rotation speed of the subject 21 is controlled by the rotating table control device 14 </ b> C using the radiation count rate obtained by the radiation detector 4 as in the first embodiment.

  Such a present Example can acquire the effect which arises in Example 1. FIG. Furthermore, since the movable carriage 7 and the first drive device 11 are not required, the configuration of the radioactivity measuring device 1A can be simplified.

  A radioactivity measurement method for radioactive waste according to embodiment 4, which is another embodiment of the present invention, will be described with reference to FIG. The radioactivity measurement apparatus 1B used in the radioactivity measurement method of the present embodiment deletes the radiation detector 4 and the collimator 5 from the radioactivity measurement apparatus 1 and uses the rotary table to obtain information on the dead time amount obtained by the pulse height analyzer 15. It is configured to input to the control device 14C. Based on the radiation count rate obtained by the radiation detector 2, the pulse height analyzer 15 obtains the energy spectrum caused by the direct line 23 and the scattered radiation 24 and the dead time amount of the radiation detector 2. This dead time amount is obtained in real time and is input to the rotary table control device 14C.

  The rotation table control device 14 </ b> C outputs a rotation control command representing the rotation speed obtained based on the dead time amount and the characteristic information of FIG. 5 stored in the storage device of the drive control device 14 to the third drive device 13. By doing so, the rotational speed of the rotary table 9 is controlled. In this way, the rotation speed of the subject 21 is controlled during radiation measurement by the radiation detector 2.

  In the present embodiment, the effects produced in the first embodiment can be obtained. Furthermore, since the radioactivity measuring apparatus 1B used in the present embodiment does not require the radiation detector 4 and the collimator 5, the structure is simplified compared to the radioactivity measuring apparatus 1.

  A radioactivity measurement method for radioactive waste according to embodiment 5, which is another embodiment of the present invention, will be described with reference to FIG. The radioactivity measurement apparatus 1C used in the radioactivity measurement method of the present embodiment has a configuration in which a count rate distribution storage device 30 is added to the radioactivity measurement apparatus 1B.

  The radioactivity measurement method according to the present embodiment detects the radiation emitted from the subject 21 with the radiation detector 2 before performing the radioactivity measurement method according to the first embodiment, and the radiation count obtained by the radiation detector 2. The amount of dead time is obtained by the wave height analyzer 15 for inputting the rate. The amount of dead time for each width ΔL obtained in advance is stored in the count rate distribution storage device 30.

  When performing radioactivity measurement of the subject 21 based on information obtained by radiation measurement using the radiation detector 2 similar to that in the first embodiment, the information on the dead time amount stored in the count rate distribution storage device 30 is represented by the width ΔL. The rotational speed of the subject 21 is controlled for each use. That is, the rotation table control device 14C represents the rotation speed obtained based on the dead time amount stored in the count rate distribution storage device 30 and the characteristic information of FIG. 5 stored in the storage device of the drive control device 14. By outputting a rotation control command to the third drive device 13, the rotation speed of the turntable 9 is controlled.

  In the present embodiment, the effects produced in the fourth embodiment can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the radioactivity measuring apparatus used for the radioactivity measurement method of the radioactive waste of Example 1 which is one suitable Example of this invention. It is explanatory drawing which shows the state of the height direction which put the subject on the rotary table shown in FIG. It is explanatory drawing which showed typically the dependence of the position of the radionuclide in the radial direction of a subject of the geometric efficiency in consideration of rotation of the subject (storage container). It is explanatory drawing which shows an example of the relative moving speed of a subject and a radiation detector. It is the characteristic view which showed the relationship between the rotational speed of a test object and the dead time (or radiation count rate) of a radiation detector. It is explanatory drawing which shows the scanning range of the axial direction of a subject. It is a characteristic view which shows a measurement spectrum, a scattered ray intensity, and a direct line intensity in case Co-60 and Cs-137 exist in the same distribution in a subject. It is a characteristic view which shows the relationship between the spectrum parameter | index in case Co-60 and Cs-137 exist in a subject with the same distribution, and attenuation in the storage container of a direct line | wire. It is a block diagram of the radioactivity measuring apparatus used for the radioactivity measurement method of the radioactive waste of Example 2 which is another Example of this invention. It is a block diagram of the radioactivity measuring apparatus used for the radioactivity measurement method of the radioactive waste of Example 3 which is another Example of this invention. It is a block diagram of the radioactivity measuring apparatus used for the radioactivity measurement method of the radioactive waste of Example 4 which is another Example of this invention. It is a block diagram of the radioactivity measuring apparatus used for the radioactivity measurement method of the radioactive waste of Example 5 which is another Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C ... Radioactivity measuring device, 2, 4 ... Radiation detector, 3, 5 ... Collimator, 6 ... Storage container moving device, 7 ... Moving cart, 8 ... Lifting table, 9 ... Turning table, 11 DESCRIPTION OF SYMBOLS 1st drive device, 12 ... 2nd drive device, 13 ... 3rd drive device, 14 ... Drive control device, 14A ... Moving cart control device, 14B ... Lifting table control device, 14C ... Rotary table control device, 15 ... Photoelectric Peak computing device, 17 ... spectrum index computing device, 18 ... radioactivity computing device, 23 ... direct line, 24 ... scattered ray.

Claims (6)

  The rotating table on which the storage container containing the radioactive waste is placed is rotated, the radiation emitted from the rotating storage container is detected by the first radiation detector to obtain the radiation count rate, and the rotating table is rotated. The radiation emitted from the storage container is detected by the second radiation detector, and the rotation speed of the rotary table on which the storage container is placed is controlled based on the radiation count rate when the radiation is detected by the second radiation detector. And measuring the radioactivity intensity of the storage container based on a radiation detection signal from the second radiation detector.   The radioactive waste radioactivity measurement method according to claim 1, wherein a relative position in a horizontal direction of the storage container, the first radiation detector, and the second radiation detector is changed. Scanning the first radiation detector and the second radiation detector within a cross section with the storage container rotates each of the first radiation detector and the second radiation detector within the certain cross section. radioactivity measurement method for radioactive waste according to claim 1 performed by Rukoto changing each direction in the so horizontally direction of the first radiation detector and the second radiation detector.   An energy spectrum of the detected radiation is obtained based on a radiation detection signal from the second radiation detector, and a scattered radiation intensity and a non-scattered radiation intensity of the radiation obtained based on the energy spectrum are obtained, and the scattered radiation intensity is obtained. The spectrum index is obtained using the non-scattering ray intensity, and the radioactivity intensity in the storage container is obtained based on the spectrum index, the scattered ray intensity, and the non-scattering ray intensity. Method for measuring radioactivity of radioactive waste. The detection of the radiation by the first radiation detector is performed by arranging a first collimator in front of the first radiation detector, and the detection of the radiation by the second radiation detector is performed by the second radiation detection. The radioactive waste radioactivity measurement method according to any one of claims 1, 2, and 4, wherein the second collimator is disposed in front of the vessel. The detection of the radiation by the first radiation detector is performed by arranging a first collimator in front of the first radiation detector, and the detection of the radiation by the second radiation detector is performed by the second radiation detection. The second collimator is disposed on the front surface of the device, and when the orientation of the first radiation detector in the horizontal direction is changed, the first radiation detector and the first collimator are rotated together to produce the second radiation. The radioactive waste radioactivity measurement method according to claim 3, wherein when the orientation of the detector in the horizontal direction is changed, the second radiation detector and the second collimator are rotated together.

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