JP2008139094A - Radioactivity measuring method and instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radioactivity measuring method for accurately measuring the radioactivity concentration of a radioactive body whatever the density and radioactivity concentration distribution of the radioactive body may be, and a compact and low-cost radioactivity measuring instrument. <P>SOLUTION: According to this method, radiations emitted from the radioactive body are detected (a) to find (c) the amount of partial radioactivity caused by a specific nuclide contained in the radioactive body. Data (b) on the amount of radioactivity previously obtained as to all nuclides contained in the radioactive body are converted by means of the amount of partial radioactivity to find (d) the total amount of radioactivity in the radioactive body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radioactivity measuring apparatus and method for measuring the radioactivity of a radioactive object such as radioactive waste.

  Currently, the reprocessing of spent nuclear fuel is outsourced to a foreign reprocessing plant, and the radioactive waste generated during the reprocessing is returned to Japan together with the uranium and plutonium obtained by the reprocessing. It will be disposed of at the processing facility. Prior to disposal, various inspections and measurements such as appearance inspection, surface contamination inspection, and radioactivity measurement are to be carried out with domestic inspection equipment based on Japanese regulations. Inspection and measurement with domestic inspection equipment is also aimed at validating manufacturing records and measurement records of radioactive waste.

  Already, high-level vitrified bodies generated by reprocessing overseas have been measured for radioactivity by the following methods using domestic inspection equipment. That is, radioactive waste is installed on a drive device that can rotate and move up and down, and the entire waste is externally removed by a Ge detector for measuring the radioactivity of γ nuclides and a neutron detector for measuring the radioactivity of α nuclides. Measurement is performed by scanning in a spiral pattern. For γ nuclides, the γ-ray energy spectrum measured by the Ge detector is analyzed to determine the photoelectric peak count rate of γ rays specific to the radioactive elements contained in the radioactive waste. Multiplying by the activity conversion factor, it is converted to the radioactivity of the nuclide, and the radioactivity concentration of the γ nuclide is confirmed. For α nuclides, the validity of the radioactivity concentration of α nuclides is confirmed by multiplying the coefficient value measured by a neutron detector by a radioactivity conversion coefficient based on detection efficiency or the like (see Patent Document 1).

  In the future, in addition to the high-level vitrified material described above, the hull end pieces and miscellaneous solid waste generated during reprocessing of spent nuclear fuel overseas will be compressed into a stainless steel cylindrical container called a canister. There are plans to return the multi-packaged solid containers to Japan.

Since the amount of radioactivity in the solid container cannot be quantified by analyzing the sample before processing, the amount of radioactivity is planned to be quantified by the following method overseas. That is, a measurement device that quantifies the amount of radioactivity of γ-ray emitting nuclides by performing γ-ray spectrum measurement using a drive mechanism of the container and a plurality of γ-ray detectors arranged in the height direction, and the surroundings of the container Measured using a neutron measuring device that measures the passive neutrons by spontaneous fission and (α, n) reaction, and the prompt and delayed neutrons emitted from the neutron source by the nuclear reaction, using a number of neutron detectors I do. Of the γ radioactivity measurement results, the burnup / cooling period of the spent fuel is obtained from the ratio of the radioactivity amounts of europium 154 and cesium 137, and the Pu, Cm, and total α radioactivity amounts are obtained from the passive and active neutron measurement results.
Japanese Patent Publication No. 6-84589

  The above-mentioned conventional radioactivity measurement method and apparatus are intended for radioactive wastes having a uniform density and radioactive distribution such as vitrified bodies, and when applied to those containing such radioactive wastes. Measurement can be performed with relatively good accuracy, and since the configuration is extremely simple, there are advantages in terms of cost, maintenance, and the like.

  However, when measuring solid containers that are planned to be received in the future and that may be unevenly distributed in the density and radioactivity distribution, the measurement accuracy will deteriorate, and returned waste from overseas may not be accepted. There is sex. Further, in the case of the radioactivity measurement method planned overseas for the solid object container, there is a problem that the measuring apparatus becomes large and complicated, and the operation cost increases.

  The present invention provides a radioactivity measurement method and a compact and low-cost radioactivity measurement apparatus capable of accurately measuring the radioactivity concentration of a radioactive object regardless of the density and radioactivity concentration distribution of the radioactive object. With the goal.

  In order to achieve the above object, the radioactivity measurement method of the present invention detects radiation emitted from a radioactive object, obtains an energy spectrum of the detected radiation, and determines a specific spectrum included in the radioactive object from the energy spectrum. A method is used in which a partial radioactivity amount by a nuclide is obtained, and the partial radioactivity amount is compared with the radioactivity data obtained in advance for the nuclide contained in the radioactive object to obtain the total radioactivity amount of the radioactive object.

  In the radioactivity measurement method of the present invention, radiation emitted from a radioactive object is detected, a dose rate by a specific nuclide is obtained from the detected radiation, and radiation obtained in advance for the nuclide contained in the radioactive object is obtained. The energy spectrum from each nuclide of the capacity data is calculated, and the dose rate is compared with the radiation dose calculated from the energy spectrum to obtain the total radioactivity of the radioactive object.

  A radioactivity measurement apparatus according to the present invention includes a radiation detector that detects radiation emitted from a radioactive object, a radiation analyzer that obtains an energy spectrum of the detected radiation, and a specification included in the radioactive object from the energy spectrum. A radioactivity calculator that calculates the total radioactivity of the radioactive object by determining the partial radioactivity by the radionuclide and comparing the partial radioactivity with the radioactivity data obtained in advance for the nuclide contained in the radioactive object; It is assumed that it is equipped.

  The radioactivity measurement apparatus of the present invention includes a radiation detector that detects radiation radiated from a radioactive object, a dose rate calculation device that determines a dose rate due to a specific nuclide from the detected radiation, and the radioactive object. Radiation for calculating the total radioactivity of the radioactive object by calculating the energy spectrum from each nuclide of the radioactivity data obtained in advance for the nuclide to be obtained and comparing the dose rate with the radiation dose calculated from the energy spectrum It is set as the structure provided with capability calculation apparatus.

  According to the present invention, the radioactive concentration of a radioactive object can be accurately measured regardless of the density of the radioactive object and the radioactive concentration distribution.

Hereinafter, first to fifth embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a configuration of a radioactivity measuring apparatus in the present embodiment. That is, the radiation 3 emitted from the radiation source 2 in the radioactive object 1 is detected by the radiation detector 4. The output of the radiation detector 4 is input to the radiation analyzer 5, and the radiation analyzer 5 obtains the energy spectrum of γ rays emitted from the radioactive object 1 (FIG. 2 (a)). The energy spectrum that is the output of the radiation analyzer 5 is input to the radioactivity calculator 6, and the radioactivity calculator 6 calculates and calculates the radioactivity in the radioactive object 1 (FIG. 2 (d)).

  Here, as shown in FIG. 2 (b), data obtained by measuring the amount of radioactivity for each of the nuclides a to i is obtained in advance, and one or a plurality of nuclides are obtained by the radioactivity measuring apparatus as shown in FIG. 2 (c). The total amount of radioactivity of the radioactive object 1 is obtained by measuring the amount of radioactivity, comparing with the data, and performing proportional calculation.

  As described above, according to the radioactivity measurement method and apparatus of the present embodiment, it is possible to obtain the total radioactivity of the radioactive object 1 only by actually measuring a specific one of the radiation 3 emitted from the radioactive object 1. .

(Second Embodiment)
3 and 4 are diagrams showing a second embodiment of the present invention. That is, as shown in FIG. 3, the dose rate calculation device 7 is provided to determine the dose rate of radiation emitted from the radiation source 2 in the radioactive object 1.

D：線量率
E：放射線のエネルギー
N(E)：パルス波高スペクトル
G(E)：スペクトル−線量率変換係数 At this time, as shown in FIG. 4 (a), data obtained by measuring the radioactivity for each of the nuclides ai are obtained in advance, and the radiation spectrum from each nuclide ai of this data is calculated (FIG. 4 ( b)), by comparing the radiation dose calculated by the following equation (1) from this energy spectrum (FIG. 4 (c)) and the measured radioactivity of the specific nuclide (FIG. 4 (d)), the radioactive object 1 Is calculated (FIG. 4 (e)).

D: Dose rate
E: Radiation energy
N (E): Pulse height spectrum
G (E): Spectrum-dose rate conversion factor

  As described above, according to the radioactivity measurement method and apparatus of the present embodiment, it is possible to obtain the total radioactivity of the radioactive object 1 only by actually measuring a specific one of the radiation 3 emitted from the radioactive object 1. .

(Third embodiment)
In the third embodiment of the present invention, in the first and second embodiments, the radioactive object 1 is installed in the driving device 8 as shown in FIG. Alternatively, the radioactivity is measured while simultaneously rotating and moving up and down. According to the radioactivity measurement apparatus of the present embodiment, even when the radioactivity in the radioactive object 1 is unevenly distributed, the influence of the uneven distribution can be reduced and the amount of radioactivity can be accurately measured.

(Fourth embodiment)
As shown in FIG. 6, the fourth embodiment of the present invention is equipped with radiation detectors 4 corresponding to the number of radioactive objects 1 when there are a plurality of radioactive objects 1 in the measurement object 9. With such a configuration, it is possible to measure the radioactivity of the plurality of radioactive objects 1.

(Fifth embodiment)
The fifth embodiment of the present invention has a configuration in which conversion coefficient input means 10 is provided as shown in FIG. If the radioactivity distribution in the radioactive object 1 is not uniform in the axial direction or the horizontal direction, the radioactivity concentration can be obtained even when the radioactivity distribution is non-uniform by multiplying the measurement result by a conversion factor that takes into account the distribution. Can be evaluated with high accuracy. Moreover, by setting this conversion factor to the safe side, the radioactivity can be measured without underestimating the content of the radionuclide.

  Further, calibration is performed using a radioactive object simulating a state in which radioactivity is distributed at a position where detection sensitivity is low, and a conversion factor on the safe side can be determined by determining a conversion factor from this result.

The block diagram which shows the structure of the radioactivity measuring apparatus of the 1st Embodiment of this invention. The flowchart which shows the radioactivity measurement method of the 1st Embodiment of this invention. The block diagram which shows the structure of the radioactivity measuring apparatus of the 2nd Embodiment of this invention. The flowchart which shows the radioactivity measurement method of the 2nd Embodiment of this invention. The figure which shows the structure of the radioactivity measuring apparatus of the 3rd Embodiment of this invention. The figure which shows the structure of the radioactivity measuring apparatus of the 4th Embodiment of this invention. The block diagram which shows the structure of the radioactivity measuring apparatus of the 5th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Radioactive object, 2 ... Radiation source, 3 ... Radiation, 4 ... Radiation detector, 5 ... Radiation analyzer, 6 ... Radioactivity calculation apparatus, 7 ... Dose rate calculation apparatus, 8 ... Drive apparatus, 9 ... Measurement object 10: Conversion coefficient input means.

Claims (10)

  Radiation emitted from a radioactive object is detected, an energy spectrum of the detected radiation is obtained, a partial radioactivity amount due to a specific nuclide contained in the radioactive object is obtained from the energy spectrum, and the partial radioactivity amount is obtained as the radioactive object A radioactivity measurement method, wherein the total radioactivity of the radioactive object is determined by comparing with radioactivity data obtained in advance for nuclides contained in the radionuclide.   Detecting radiation radiated from a radioactive object, obtaining a dose rate by a specific nuclide from the detected radiation, energy spectrum from each nuclide of radioactivity data obtained in advance for the nuclide included in the radioactive object And calculating the total radioactivity of the radioactive object by comparing the dose rate with the radiation dose calculated from the energy spectrum.   The radioactivity measurement method according to claim 1 or 2, wherein the radioactive object is installed in a rotatable drive device, and the radiation emitted from the radioactive object is detected while rotating the radioactive object.   The radioactivity measurement method according to claim 1, wherein the radioactive object is installed in a drive device capable of raising and lowering the radioactive object, and radiation emitted from the radioactive object is detected while raising and lowering the radioactive object.   The radioactivity measurement method according to claim 1 or 2, wherein when the measurement object has a plurality of radioactive objects, a radiation detector corresponding to the number of the radioactive objects is used.   The radioactivity measurement method according to claim 1, wherein when the radioactivity distribution in the radiological object is not uniform, the total radioactivity amount is multiplied by a conversion factor of a ratio to the case of homogeneity.   The radioactivity measurement method according to claim 6, wherein the conversion factor is set to a safe side so that the content of the radionuclide is not underestimated.   The radioactivity measurement method according to claim 7, wherein the conversion factor is determined by performing calibration using a radioactive object simulating a state where radioactivity is distributed at a position where detection sensitivity is low.   A radiation detector for detecting radiation radiated from a radioactive object, a radiation analyzer for obtaining an energy spectrum of the detected radiation, and determining a partial radioactivity amount due to a specific nuclide contained in the radioactive object from the energy spectrum; A radiation amount calculating device for determining the total amount of radioactivity of the radioactive object by comparing the partial activity amount with the radioactivity amount data obtained in advance for the nuclide contained in the radioactive object; Performance measuring device.   A radiation detector for detecting radiation emitted from a radioactive object, a dose rate calculation device for obtaining a dose rate of a specific nuclide from the detected radiation, and a radioactivity obtained in advance for the nuclide contained in the radioactive object A radioactivity calculator that calculates an energy spectrum from each nuclide of data, and compares the dose rate with a radiation dose calculated from the energy spectrum to obtain a total radioactivity of the radioactive object. Characteristic radioactivity measuring device.

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