JP2736189B2 - Radioactive waste contamination / activation radioactive identification method with openings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for identifying radioactive waste contamination / activated radioactivity used in the treatment of waste generated during the dismantling of an aging nuclear reactor, and more particularly to piping and valves. The present invention relates to a method for discriminating contamination / activated radioactivity by using γ-ray scattering or the ratio of β-ray and γ-ray to waste having such an opening.

[0002]

2. Description of the Related Art When dismantling an aging nuclear reactor,
It is necessary to identify whether the generated waste is contaminated or radioactive.

Conventionally, a method shown in FIG. 13 has been known as a method for identifying contamination / activation radioactivity. In this method, as shown in FIG. 1A, in order to identify whether the waste is a contaminant or a radioactive material, the radiation detectors 1a and 1b are sandwiched by a flat object S to be measured. Are placed in a shielding container 2 at 180-degree symmetrical positions, and the ratio of scattered γ-rays / direct γ-rays of the radiation detectors 1a and 1b is compared. The ratio of scattered γ-rays / direct γ-rays is different, but the ratio of activated materials is not different. In the method shown in FIG. 2B, four radiation detectors 1a, 1b, 1c and 1d are arranged at 90-degree intervals so that both sides can be measured regardless of the measurement position of the measurement target S. Thus, contamination / activation of the measurement object S is identified. Further, in the method shown in FIG. 2C, only one radiation detector 1a is used, and the radiation detector or the measurement object S is rotated by 180 degrees to obtain 2
By comparing the ratio of the scattered γ-ray / direct γ-ray measured twice, contamination / activation of the measurement target S is identified.

A method is also known in which the ratio of β-rays to γ-rays is used instead of the ratio of scattered γ-rays / direct γ-rays. In this method, as shown in FIG.
As shown in FIG. 3A, two radiation detectors 6a and 6
b is arranged 180 degrees symmetrically with the plate-like measurement object S interposed therebetween, or as shown in FIG. 3B, one radiation detector 6 is used, and the radiation detector 6 or the measurement object S is used. Is rotated by 180 degrees, and the contamination / activation of the measurement target S is identified by comparing the β-ray / γ-ray ratio measured twice.

[0005]

However, in the conventional method described above, the radiation detector 1a, 1b,
6a and 6b are simply set to 18 so as to measure the surface of the object to be measured.
When symmetrically arranged at 0 degrees, the scattered γ-ray / direct γ-ray ratio and β-ray / γ-ray ratio obtained from the radiation detector become equal. Can not.

Therefore, in the conventional method, when the contamination / activation of the waste having the opening is identified, the object to be measured is rotated. However, in the case of a large waste, the object to be measured is rotated. It is extremely difficult to rotate things,
In addition, since the same measurement target is measured twice, it is extremely inefficient when treating a large amount of waste, and furthermore, there is a drawback that the risk of exposure of workers is increased correspondingly.

The present invention has been made to eliminate the above-mentioned drawbacks in the prior art.

[0008]

According to the first aspect of the present invention, there is provided a light emitting device.
Using a radiation detector that detects lines, a system that analyzes the signal from the radiation detector, and a computer that calculates, evaluates, and displays the analyzed signal, radioactive waste having an opening In the method of identifying contaminated / activated radioactivity, the radiation detector is used
Gamma ray spectrum and gamma rays from directions other than the aperture
The step of measuring the spectrum and the gamma ray scanning from the opening direction
Obtaining a ratio of scattered γ-rays and direct γ-rays from the spectrum,
Scattering γ from γ-ray spectrum from directions other than the opening
The step of directly determining the ratio of the line and the γ-ray, from the opening direction
To the ratio of scattered γ-rays / direct γ-rays other than the apertures
For calculating the ratio of the ratio of scattered γ-rays / direct γ-rays from different directions
And radioactive waste is contaminated based on this calculated ratio.
And a step of distinguishing between an object and a radioactive substance . The invention according to claim 2 detects radiation.
Radiation detector and the signal from this radiation detector
System to analyze and calculate and evaluate this analyzed signal
Radioactive waste with openings using a computer
A method for identifying waste contamination / activation radioactivity
Β-rays from the opening direction of radioactive waste by radiation detector
Measuring γ-rays and γ-rays to determine the measurement ratio;
X-ray detector detects radioactive waste from directions other than the opening
measuring β-rays and γ-rays and determining the measurement ratio;
The measurement ratio of β-ray / γ-ray from the opening direction and the opening
Calculate the ratio with the measurement ratio of β-ray / γ-ray from directions other than
From the calculated ratio and the calculated ratio.
Radioactivity and radiation of pollutants in radioactive waste with mouth
Based on the change curve of the ratio according to the ratio of
Process to identify whether radioactive waste is contaminated or radioactive
It is characterized by having.

[0009]

According to the method of the present invention having the above structure, the work efficiency can be improved without losing the purpose of discriminating between contaminants and radioactive substances,
The danger of worker exposure can be reduced, and a large amount of waste generated at the time of dismantling of an aging nuclear reactor can be measured quickly and accurately. That is, as shown in FIG.
When the measurement object P having an opening is an inner surface contaminant,
The radiation detector 1a facing the opening mainly detects a large amount of direct γ-rays from the measurement object P, while the radiation detector 1b not facing the opening detects the γ-rays scattered in the measurement object P. Is detected more than the radiation detector 1a facing the opening, the ratio between the count value of the scattered γ-rays and the count value of the direct γ-rays of both the radiation detectors 1a and 1b (hereinafter, scattered γ-ray / (Referred to as the direct γ-ray ratio). On the other hand, as shown in FIG. 3A, when the measurement object P is a radioactive substance, both the radiation detector 1a facing the opening and the radiation detector 1b not facing the opening have much scattering. γ-rays are detected, and both radiation detectors 1a and 1b are detected.
There is almost no difference in the ratio of scattered γ-rays / direct γ-rays obtained from the above. Therefore, the scattered γ-rays of the radiation detectors 1a and 1b /
By directly comparing the gamma ray ratios, it is possible to distinguish between contaminants and radioactive materials.

This is, as shown in FIG. 4A, a radiation detector 6 in which a γ-ray detector 4 and a β-ray detector 5 are combined.
The same is true for measurement using a and 6b. That is, when the measurement object P having the opening is the inner surface contaminant, the β-ray detector 5 of the radiation detector 6a facing the opening detects the β-ray from the inner surface contaminated surface, and turns to the opening. The γ-ray detecting section 4 of the radiation detector 6a detects a large amount of γ-rays from the inner contaminated surface. On the other hand, the β-ray detector 5 of the radiation detector 1b that is not directed to the opening cannot detect the β-ray because the β-ray is shielded by the measurement object P itself, but the γ-ray has a large material transmission ability. Is not shielded by the measurement object P, and thus is also detected by the γ-ray detection unit 4 of the radiation detector 6b not facing the opening. Accordingly, the ratio of the β-ray counting rate of the β-ray detecting section 5 of the radiation detector 6a facing the opening to the γ-ray counting rate of the γ-ray detecting section 4, and the β of the radiation detector 6b not facing the opening. There will be a difference between the ratio of the count rate of β rays by the line detector 5 and the count rate of γ rays by the γ ray detector 4. On the other hand, as shown in FIG. 5A, when the measurement object P is a radioactive substance, the β-ray counting rate and the γ-ray detection section 4 by the β-ray detection section 5 of the radiation detector 6a facing the opening are shown. Is small, and the difference between the ratio of the count rate of the γ-rays by the γ-ray detector 4 and the count rate of the γ-rays by the β-ray detector 5 of the radiation detector 6b not facing the opening is small. Therefore, the difference in the count rate ratio between β-rays and γ-rays detected by the radiation detector 6a facing the opening and the radiation detector 6b not facing the opening is small, and therefore, both radiation detectors 6a, 6a, By comparing the β- / γ-ray count rate ratio of 6b, it is possible to distinguish between contaminants and radioactive substances.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, for example, a measurement object P having an opening, such as a pipe, is placed at the center, and a radiation detector 1a is arranged around the measurement object P at a position facing the opening, and at a position not facing the opening. The radiation detectors 1b are arranged, and their surroundings are covered with the shielding container 2. The outputs of the radiation detectors 1a and 1b are processed by the signal processing means 10a and 10b, the obtained signals are calculated by the calculator 11, and the results are displayed.

In FIG. 2A, when the measurement object P is, for example, a contaminant of Co-60 without an activated portion, the radiation detector 1a facing the opening and the radiation detection not facing the opening are detected. The output display of the measurement result of the device 1b is as follows.
The γ-ray spectra 20a and 20b in FIG. In the figure, 21a and 21b are radiation detectors 1
a and 1b show the counts of the direct gamma rays measured at 22a and 2b.
2b shows the count of scattered γ-rays measured by the radiation detectors 1a and 1b. The direct gamma ray count 21a of the gamma ray spectrum 20a is equal to the direct gamma ray count 2 of the gamma ray spectrum 20b.
1b. As is clear from this figure, the scattered gamma ray count 22a measured by the radiation detector 1a facing the opening is larger than the scattered gamma ray count 22b measured by the radiation detector 1b not facing the opening. Relatively few.

FIG. 3 (b) shows the γ-ray spectra 23a and 23b of the radiation detectors 1a and 1b when the measurement object P is an activated substance having no contaminated portion. In the figure, 24
a and 24b are the direct γ values measured by the radiation detectors 1a and 1b.
The line count is shown, and 25a and 25b are radiation detectors 1a,
The scattered gamma ray count measured in 1b is shown. The direct gamma ray count 24a of the gamma ray spectrum 23a is shown normalized to the direct gamma ray count 24b of the gamma ray spectrum 23b. Unlike the case of the contaminant shown in FIG. 2, in the case of the radioactive material of FIG. 3, the ratio of the scattered γ-ray count 25a measured by the radiation detector 1a facing the opening and the direction of the opening are not directed. Count 25b of scattered γ-rays measured by the radiation detector 1b
Are almost equal.

FIG. 6 shows the measurement results of the γ-ray spectrum shown in FIG. 2 (b) of a measurement object having an opening in which a contaminated part and an activated part are mixed, while changing the ratio of the contaminated part and the activated part variously. The ratio of the direct gamma ray count 21b and the scattered gamma ray count 22b measured by the radiation detector 1b not facing the opening to the ratio of the direct gamma ray of the contaminated part measured by the radiation detector 1a facing the opening to the ratio 22b. The ratio of the ratio of the count 21a to the count 22a of the scattered γ-rays is plotted on the vertical axis, and the ratio of the radioactivity of the contaminated portion and the radioactive portion of the object to be measured is plotted on the horizontal axis. As is clear from this figure, the ratio of the vertical axis increases from about 1 to about 3.5 as the ratio of the contaminated portion of the measurement object increases. It can be seen that the discrimination between the contaminant and the radioactive material is good because the change is sharp in the region where the ratio is about 0.1 to about 10. Although the change in the ratio between the scattered γ-rays and the direct γ-rays as shown in FIG. 6 slightly changes depending on the shape of the measurement target, the measurement data shown in FIG. 6 is prepared before the measurement of the measurement target. Thereby, contamination / activation can be easily identified.

As is clear from the above description, in the present embodiment, as shown in FIG. 1, a radiation detector 1a facing the opening and a radiation detector 1b not facing the opening are arranged around the object P to be measured. arranged to measure the γ-ray spectrum, each γ
Calculating the ratio of scattered γ-rays / direct γ-rays from the
By calculating the ratio, contamination / activation can be identified without destroying a measurement object having an opening such as a pipe .

Next, another embodiment of the present invention will be described.

As described above, when identifying contamination / activation of waste having an opening, the radiation detectors may be arranged orthogonal to each other with respect to the tubular measurement object P.
When a flat waste is measured in this arrangement, it becomes impossible to discriminate between contaminants and radioactive materials as shown in FIG. That is, the radiation detector 1a in FIG. 7A faces the contaminated surface of the measurement target S, which is a flat contaminant, and the radiation detector 1b positions the measurement target S from the side, that is, radiation detection. It is arranged orthogonal to the vessel 1a. FIG.
(B) shows the sum of the count value of the scattered γ-rays on the contaminated surface and the direct γ-rays by the radiation detector 1a when the position of the radiation detector 1b is changed in the angle θ direction so as to look into the opposite surface of the contaminated surface. Scattering γ of the opposite surface by the radiation detector 1b with respect to the numerical ratio
The state of a change in the ratio of the line count value / direct gamma ray count value ratio is shown. This ratio is an index indicating that the closer to zero, the more contaminant is present, and as this ratio is greater than zero, the number of activated parts increases. As is clear from this figure, when the angle θ of the radiation detector 1b is larger than 60 degrees, the misrecognition as a contaminant sharply increases. Therefore, by arranging the radiation detectors 1a and 1b at a predetermined angle from the orthogonal position, it is possible to discriminate between contamination and activation without selecting tubular waste and flat waste. it can.

Still further, waste having a complicated shape, for example, T
In the case of contamination / activation identification measurement of a pipe, an elbow or a valve, the radiation detector does not always face the opening of the waste. FIG. 8 shows an embodiment in which a large number of radiation detectors 1a to 1h are arranged in various directions at various angles with respect to the T-tube T. In this way, even if the waste is large, contamination / activation can be identified without moving the measurement target so that the opening of the measurement target T faces the radiation detectors 1a to 1h. Can be.

As shown in FIG. 9, a single radiation detector 1a is driven by a driving unit (not shown) that can move in all directions, and measurement is performed a plurality of times. The identification of contamination / activation of waste in complex shapes can be performed.

In the above embodiment, γ is used as the radiation detector.
Using a radiation detector that measures the X-ray spectrum, the contamination /
Although the method of identifying activation has been described, the present invention is not limited to this, and a radiation detector combining a γ-ray detector and a β-ray detector may be used.
That is, as shown in FIG. 10, radiation detectors 6a and 6b combining a γ-ray detector 4 and a β-ray detector 5 are used,
These are arranged at an appropriate angle around the measuring object P, their outputs are processed by the signal processing means 10a and 10b, the obtained signals are calculated by the calculator 11, and the results are displayed.

In FIG. 4 (a), when the measurement object P having an opening is a contaminant having no activation part, β-ray counting by the β-ray detection part 5 of the radiation detector 6a facing the opening. The ratio between the rate and the γ-ray counting rate by the γ-ray detector 4 is shown in FIG.
A curve 7a of FIG. In addition, the ratio of the β-ray counting rate of the β-ray detecting section 5 of the radiation detector 6b not facing the opening to the γ-ray counting rate of the γ-ray detecting section 4 is shown in FIG.
A curve 7b in FIG. This is because the β-rays detected by the β-ray detection unit 5 of the radiation detector 6a facing the opening correspond to the radiation detector 6b not facing the opening.
This is because the β-ray detector 5 cannot detect β-rays because the β-rays are shielded by the measurement object P itself.

In FIG. 5 (a), when the measurement object P having an opening is a radioactive material having no contaminated portion, the β-ray detector 5 of the radiation detector 6a facing the opening detects β.
The ratio between the line counting rate and the γ-ray counting rate by the γ-ray detecting unit 4 is
A curve 8a in FIG. 5B is obtained. The ratio between the β-ray counting rate of the β-ray detecting section 5 of the radiation detector 6b not facing the opening and the γ-ray counting rate of the γ-ray detecting section 4 is as shown by a curve 8b in FIG. Become.

As is apparent from a comparison between FIG. 4B and FIG. 5B, when the object P having an opening is an inner surface contaminant, the radiation detector facing the opening is used. Β of 6a
The ratio of the X-ray / γ-ray count rate is
Compared to the ratio of the β-ray / γ-ray counting rate of the output device 6b, the difference is large regardless of the diameter of the measurement target P, but when the measurement target P is an activated substance, the β-ray / Γ-ray count rate ratio
The difference is small regardless of the diameter of the measurement object P.

It should be noted that, for a measurement object P having an opening,
When the ratio of the β-ray / γ-ray count rate ratio of the radiation detector 6a facing the opening to the radiation detector 6b not facing the opening is used as a discrimination index, as shown in FIG. The discrimination index increases from 1 to 18 as the proportion of the contaminated portion of the measuring object P increases, and in particular, the contaminated portion radioactivity / activated portion release
The change is remarkable in the range of the emissivity of 0.1 to 100. Therefore, prior to the measurement of the object to be measured, FIG.
By preparing the measurement data shown , contamination / activation radioactivity of radioactive waste having an opening can be easily identified with high identification performance.

As described above, in this embodiment, a radiation detector in which a β-ray detector and a γ-ray detector are combined is used, and the radiation detector is positioned at a position facing the opening and at a position not facing the opening. To measure β-rays and γ-rays, process their output by signal processing means, and calculate the obtained signal by a computer, without destroying radioactive waste having an opening, The contamination / activation radioactivity can be distinguished.

Note that, as shown in FIG.
Radiation detectors 6a and 6 in which the radiation detectors 6 and
12b are arranged orthogonally, and when these are used to measure the flat waste S, as shown in FIG. 12B, the discrimination index changes depending on the angle θ of the detector, and θ = 90 °. Since the temperature decreases in the vicinity, the contaminated portion and the activated portion of the flat waste S may not be distinguished. In order to avoid this, the arrangement angles of the radiation detectors 6a and 6b may be shifted from around 90 °.

Also, in the case of using a radiation detector in which a β-ray detector and a γ-ray detector are combined, as in the case of FIG. Alternatively, as in the case of FIG. 9, a single radiation detector may be used and driven by a driving unit (not shown) capable of moving in all directions to perform a plurality of times. By performing the measurement, the contamination /
Activation can be identified.

[0029]

As described above, according to the present invention,
Position the radiation detector so that it faces the waste
Position it so that the, Gamma spec
Tor or gamma and beta raysBy measuring, the measurement target
Discrimination of contaminants and radioactive materials without discriminating objects by shape
Can lead to a decrease in work efficiency and exposure of workers.
Measurement of various and large amounts of wasteWhat
You.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

2A is a schematic diagram showing a difference in scattered γ-rays of contaminants depending on an angle of a radiation detector, and FIG. 2B is a graph showing an energy distribution of γ-rays.

FIG. 3A is a schematic diagram showing a difference in scattered γ-rays of a radioactive substance depending on an angle of a radiation detector, and FIG. 3B is a graph showing an energy distribution of γ-rays.

FIG. 4 (a) is a view of β of a contaminant according to the angle of a radiation detector.
It is the schematic which shows the difference of the ratio of a line and a gamma ray, and (b) is a graph which shows the relationship of the beta-ray count rate / gamma-ray count rate ratio with respect to the aperture of the object to be measured.

5 (a) is a schematic diagram showing the difference in the ratio of β-rays and γ-rays of the radioactive substance depending on the angle of the radiation detector, and FIG. 5 (b) is the β-ray counting rate / γ-rays with respect to the aperture of the measurement object. It is a graph which shows the relationship of a count rate ratio.

FIG. 6 is a graph showing the result of measuring the ratio of scattered γ-rays while changing the ratio of a contaminated portion and an activated portion of waste.

FIG. 7A is a schematic diagram showing a relationship between an angle of a radiation detector and a plate-shaped symmetric object, and FIG. 7B is a graph showing a relationship between an arrangement angle of the radiation detector and a ratio of scattered γ rays. It is.

FIG. 8 is an explanatory diagram showing an embodiment in which a plurality of radiation detectors are arranged in all directions in the present invention.

FIG. 9 is an explanatory diagram illustrating a measurement method using a radiation detector that can move in all directions in the present invention.

FIG. 10 is a plan view showing another embodiment of the present invention.

FIG. 11 is a graph showing how the discrimination index changes when the ratio of the contaminated part to the activated part of the measurement object is changed.

12A is a schematic diagram showing the relationship between the angle of a radiation detector and a flat symmetric object, and FIG. 12B is a graph showing the relationship between the arrangement angle of the radiation detector and a discrimination index.

FIGS. 13 (a) to 13 (c) are schematic views showing a prior art apparatus for discriminating contamination / activation of flat waste.

14 (a) and 14 (b) are schematic diagrams showing a conventional plate waste contamination / activation identification device, respectively.

[Explanation of symbols]

 1a to 1h radiation detector 2 shielding container 4 gamma ray detector 5 beta ray detector 6a, 6b radiation detector 10a, 10b signal processing means 11 computer

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-308590 (JP, A) JP-A-63-70186 (JP, A) Jpn.

Claims (2)

(57) [Claims] An opening is formed by using a radiation detector for detecting radiation, a system for analyzing a signal from the radiation detector, and a computer for calculating, evaluating and displaying the analyzed signal. A method for identifying contamination / activation radioactivity of a radioactive waste, comprising:
Spectrum from γ and γ from directions other than the aperture
Measuring the X-ray spectrum, and directly calculating the scattered γ-rays from the γ-ray spectrum from the opening direction.
A step of determining a ratio of tangential γ-rays, and scattering γ from a γ-ray spectrum from a direction other than the opening
A step of determining the ratio of the line and direct γ-rays, for the ratio of the scattered γ ray / direct γ-rays from the opening direction
Of the ratio of scattered γ-rays / direct γ-rays from directions other than the opening
Calculating a ratio, and the radioactive waste is contaminated based on the calculated ratio.
Pollution / emission of radioactivity identification method of radioactive waste having an opening; and a step of identifying whether things or radiation products. 2. A radiation detector for detecting radiation.
A system that analyzes the signal from the radiation detector
Calculates, evaluates, and displays the analyzed signal.
Of radioactive waste with openings / activation radioactivity
In the method of identifying the direction of the opening of the radioactive waste by the radiation detector
To measure β- and γ-rays from
And degree, the other opening of the radioactive waste by the radiation detector
Β and γ rays from different directions, and determine the measurement ratio
And the measurement ratio of β-ray / γ-ray from the opening direction and the opening
Calculate the ratio with the measurement ratio of β-ray / γ-ray from directions other than
And an opening created in advance from the calculated ratio.
Radioactivity of contaminants and radioactive emissions in radioactive waste
The radiation based on the change curve of the ratio according to the ratio of the power
Identifying whether waste is contaminant or radioactive
Of radioactive waste with openings characterized by the following:
Activation radioactivity identification method.