JPS62273479A - Radioactivity measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve a shorter time for inspecting pollution and a lower cost of an inspector, by a method wherein radiation is measured turning a radioactive waste storage container and the results of the measurement are subjected to an arithmetic processing to enable simultaneous measurement of radioactivity on the surface of the container and that therein. CONSTITUTION:A radiation detector unit 5 is arranged on the circumference of a radioactive waste storage container 1. The detector unit 5 has two radiation detectors 7 and 8 integrated and the detector 7 (e.g. plastic detector) is arranged at the front of the container 1 and the detector 8 [e.g. NaI(Tl) detector], on the surface opposite to a light receiving surface of the detector 7. The detector unit 5 measures radiation emitted from the container turning the container 1, where emission gamma rays from radioactivity on the surface of the container and that therein can be measured with the detectors 7 and 8 while as to betarays, emission beta rays alone from the radioactivity on the surface can be measured with the detector 7. Counts as measured by both the detectors 7 and 8 are subjected to an arithmetic processing by a specified formula to determine the radioactivity on the surface of the container and that therein simultaneously.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a device for measuring the surface contamination of a storage container filled with radioactive waste and the intensity of radioactivity within the container. In particular, it relates to a radioactivity measuring device that can simultaneously and remotely measure surface contamination and radioactivity intensity inside a container.

[Conventional technology]

Conventionally, as a method for measuring radioactivity adhered to the surface of a radioactive waste storage container, an automated method of measuring a smear is known, for example, as shown in Japanese Patent Application Laid-Open No. 60-93980.

Furthermore, a method is known in which the radioactivity intensity within the radioactive waste storage container is identified from the air dose rate around the storage container.

[Problem that the invention seeks to solve]

With the above conventional technology, it is not possible to simultaneously measure the degree of surface contamination of a radioactive waste storage container and the radioactivity within the container.

In order to measure the degree of contamination on the surface of the storage container and the radioactivity inside the container, two measurements, that is, two measuring devices, are required, which poses the problem of increasing the cost of the device and lengthening the inspection time. Ta.

The purpose of the present invention is to enable highly accurate surface contamination inspection regardless of the surface contamination of a radioactive waste storage container;
It is an object of the present invention to provide a contamination testing device for a radioactive waste storage container that can simultaneously measure the radioactivity in the radioactive waste storage container and that does not require human labor for the measurement work.

[Means for solving problems]

The above purpose is to integrate two radiation detectors around the outer periphery of a radioactive waste storage container, that is, a first radiation detector is placed in front of the radioactive waste storage container, and the first radiation detector is arranged in front of the radioactive waste storage container. A second radiation detector is installed on a crystal plane of the first radiation detector opposite to a light-receiving surface of the detector. This is achieved by rotating the radioactive waste storage container, measuring the radiation emitted from the storage container using the radiation detector, and calculating the measurement results.

[Effect]

Radiation emitted from the radioactivity attached to the surface of the radioactive waste storage container and the radioactivity inside the container enters the first radiation detector, causes a luminescence phenomenon, and consumes radiation energy. The radiation that is not consumed here enters the second radiation detector and causes a light emission phenomenon. Assuming that the radiation emitted from the radioactive waste storage container is β rays and γ rays, the radioactivity attached to the surface and the γ rays emitted from the radioactivity inside the container can be measured by the first and second radiation detectors. However, since β-rays have weak penetrating power, only the β-rays emitted from the radioactivity attached to the surface can be measured by the first radiation detector.

Due to the above-mentioned operating phenomenon, the first radiation detector measures the adhering radioactivity on the surface of the storage container, the gamma rays emitted by the radioactivity within the container, and the emitted beta rays from the surface adhering radioactivity. In addition, the second radiation detector measures gamma rays emitted due to surface adhesion and radioactivity within the container.

The β-ray dose can be identified by simultaneously solving equations for each radiation detector using the count values measured by these two radiation detectors. In other words, the intensity of adhering radioactivity on the surface of the radioactive waste storage container is determined. Next, the radioactive nuclide is determined by analyzing the gamma ray spectrum measured by the second radiation detector. The emitted γ-ray dose of the surface-attached radioactivity is calculated using the γ-ray emission rate per −β decay of the determined nuclide and the surface-attached radioactivity intensity, and the calculated γ-ray dose is calculated from the measured value of the second radiation detector. By subtracting the dose, the radioactivity intensity inside the storage container can be determined.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to one embodiment shown in the drawings.

FIG. 1 is a side view of an embodiment of the present invention, FIG. 2 is a sectional view of a radiation detection device, and FIG. 3 is a block diagram of a radiation measurement system and an arithmetic control section.

A radioactive waste storage container 1, which is an object to be measured, is placed on a turntable 3 that can rotate and move up and down along guide rollers 9. A guide roller 9 is installed on the pedestal 6 so that the axis of the turntable 3 and the rotation axis of the storage container 1 are concentric. A drive shaft of the turntable 3 is connected to a vertical rotation control drive device 4.
The position of the storage container 1 can be freely changed in the vertical and rotational directions based on the drive of the storage container 1. Further, a weight detector 2 for measuring the total weight of the storage container 1 is installed on the turntable 3. A radiation detection device 5 that measures radiation emitted from the waste storage container 1 is fixed to a pedestal 6 and placed at a position facing the side surface of the storage container 1. Furthermore, the radiation detection device 5 includes two radiation detectors 7 and 8, as shown in FIG.
It is composed of a shielding wall 10 that shields radiation incident from other than the light-receiving surfaces of the radiation detectors 7 and 8, a collimator 13 that determines geometric efficiency, and a case 11 that fixes it. A first radiation detector 7 is installed in the opening of the radiation detection device 5.
1. For example, a plastic detector is placed, and a second radiation detector 8, such as a NaI (TQ) detector, is placed on a surface opposite to the light-receiving surface of the plastic detector 7. The plastic detector 7 and the NaI (TQ) detector 8 are integrally processed and are surrounded by a shielding wall 1o. Shielding wall 10
A plastic detector 7 and a NaI ("rc) detector 8 wrapped in a plastic detector are fixed to a case 11.

Further, the collimator 13 is installed in front of the plastic detector 7.

FIG. 3 shows the process of processing the output signals of the plastic detector 7 and NaI (T(1) detector 8) that measure the radiation emitted from the storage container 1.
The output signal of the I(TQ) detector 8 is transmitted to each linear amplifier 12a.
, L2b performs waveform shaping and amplification processing of the peak value. The count value of the amplified plastic detector 7 signal is measured by a counter 14. Further, when the output signal of the NaI (TQ) detector 8 is input to the radiation pulse height analyzer 15, the radiation count value is counted for each radiation energy range defined by the pulse height analyzer 15. counter 14
The output of , and the output of the radiation wave height analyzer 15 are automatically taken into the computing unit 16, and by performing arithmetic processing in the computing unit 16, the intensity of the radioactivity attached to the surface of the storage container 1 and the radioactivity inside the container are identified. . The intensity results of the identified radioactivity are output to the display device 17 and stored in the storage device 18. Further, the computing unit 16 has a function of reading out the results of the already measured radioactivity on the surface of the storage container 1 and the radioactivity inside the container from the storage device 18 and outputting them to the display device 17 based on instructions from the operator console 19. There is. In addition, arithmetic unit 16
controls the vertical rotation control drive device 4 to rotate the storage container 1
The relative position between the radiation detecting device 5 and the radiation detecting device 5 can be freely changed.

Also.

The computing unit 16 also has a function of reading the output signal of the weight detector 2 installed on the turntable 3.

Next, a method for identifying the radioactivity attached to the surface of the storage container 1 and the radioactivity intensity inside the container, that is, a measurement principle and a calculation method will be explained.

If the crystal of the plastic detector 7 is placed with a certain thickness, the β rays incident on the plastic detector 7 will consume all the energy in the crystal and cause a luminescence phenomenon. In addition, the γ-rays lose some energy in the plastic detector 7 and become NaI (TQ).
incident on the detector 8.

The γ-rays incident on the N a I' (T Q ) detector 8 consume all of their energy in the NaI (TQ) crystal. That is, the − incident γ-ray causes a luminescence phenomenon in two radiation detectors (plastic detector 7 and NaI (TQ) detector 8). The and β rays cause a luminescence phenomenon only in the plastic detector 7.

Therefore, in the process of controlling the vertical rotation control drive device 4 to rotate the turntable 3 and measuring the radiation emitted by the storage container 1 while rotating the storage container 1 installed on the turntable 3, Take advantage of phenomena. The count value measured by the plastic detector 7 at this time is Cp,
The count value measured by the Na I (Tfl) detector 8 is
If the density distribution of the contents of the storage container 1 is constant and the radioactivity attached to the surface and the radioactivity inside the container are equal, then Cp and CN can be expressed by the following equations.

Cp=Ao? 1oω+A,? Joω-・-o)CN=A
oG (y)'+,c,++A,? ? , ω - (2) However, Ao in the above equation is the total number of photons of β rays and γ rays due to the radioactivity attached to the surface of the storage container 1 at the current measurement position, and A1 is the emission due to the radioactivity inside the storage container 1. It is the number of gamma rays. and η0
is the counting efficiency of the plastic detector 7, η□ is NaI(T
Q) The counting efficiency of the detector 8, G(γ) is the ratio of emitted γ-rays to the total value of emitted β-rays and γ-rays in the −β decay of surface-attached radioactivity, and ω is the geometric efficiency. This (1).

By solving equations (2) simultaneously, Ao and A□ can be obtained.

Next, the arithmetic processing method for the above equations (1) and (2) will be described. η0 in equations (1) and (2). Since η is a factor determined by the crystal shape of each radiation detector, it is calculated in advance and stored in the calculator 16. Similarly, ω is a factor determined by the shape of the opening of the collimator 13, so it is calculated in advance and stored in the calculator 16. The arithmetic unit 16 calculates the η0.
Using η1 and ω, transform equations (1) and (2) as follows: η0ω η1ω Here, subtract equation (2') from equation (1') to obtain equation 3).

This equation (3) means the detected β-dose of radioactivity attached to the surface of the storage container 1 at the measurement position. In other words, it indicates the intensity of radioactivity attached to the surface.

Next, the computing unit 16 performs peak search processing on the gamma ray spectrum determined by the NaI (TQ) detector 8, determines the central energy value of the peak, and determines the peak of the radioactive substance held in the table in the computing unit 16. The energy value and the search peak energy value are compared to identify the nuclide of the measured radioactivity. In other words, since G(γ) for each radioactive substance is constant, by identifying the nuclide, the amount of γ-rays released due to surface-attached radioactivity A
o G (γ) can be expressed by the following formula.

However, Ao(β) in equation (4) is the release β of surface-attached radioactivity.
It is the dose.

If we substitute equation (4) into equation (2') and perform the arithmetic processing, A
You can find d.

Further, since the storage container 1 is usually a 200Q drum pipe, the volume of the storage container 1 is known. The total weight of the storage container 1 is measured by the weight detector 2 on the turntable 3, and the measurement result is transmitted to the calculator 16. Arithmetic unit 16
The density of the contents is determined from the volume and weight of the storage container 1.

The radiation attenuation rate μ is estimated from this calculated density, and the A
□.

When μ is used, the radioactivity intensity Io of the contents of the storage container 1 at the measurement position (cross section) can be expressed by the following equation.

However, μ2 is the radiation attenuation rate of the storage container 1, t is the thickness of the storage container 1, and D is the inner diameter of the storage container 1.

Therefore, by processing equation (5) with the calculator 16, the radioactivity intensity within the storage container 1 can be determined.

Here, the vertical rotation control drive device 4 is controlled to move the turntable 3 connected to the control drive device 4 up and down. That is, the relative position between the storage container 1 placed on the turntable 3 and the radiation detection device 5 is changed, and the adhering radioactivity on the surface of the storage container 1 and the radioactivity inside the container at that position (cross section) are measured by the above method. Find it by By continuously performing this measurement on the entire surface (cross section) of the storage container 1, the degree of contamination of the entire surface of the storage container 1 and the radioactivity intensity within the container can be quantified.

〔Effect of the invention〕

As explained above, according to the present invention, radiation is measured while rotating the radioactive waste storage container on the assumption that the density distribution of the contents of the radioactive waste storage container is constant, and calculation processing is performed on the measurement results. By carrying out this method, the radioactivity attached to the surface of the radioactive waste storage container and the radioactivity inside the container can be measured simultaneously, which has the effect of shortening the time for contamination inspection and lowering the cost of the contamination inspection equipment. Furthermore, since no human labor is required for contamination inspection, it is effective in reducing the amount of radiation exposure.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of a radiation detection device, and FIG. 3 is a block diagram of a radiation measurement system and an arithmetic control section.

Claims (1)

[Claims] 1. A radiation detection device that measures radiation emitted from an object to be measured, a movement mechanism that moves the object to be measured vertically and rotationally, and a scale that measures the weight of the object to be measured;
a calculation device that performs calculation processing on the output signal of the radiation detection device;
A radioactivity measuring device comprising: a display device that displays calculation results; and a storage device that stores calculation results.