JPH10288667A - Radioactivity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To approach a measuring object and efficiently measure radioactivity by using a plastic scintillation fiber scope for the detector of radioactivity meter. SOLUTION: A worker 1 receiving contamination inspection goes in a gate monitor 4, turns on a switch for measurement and moves a distance measuring sensor 6 to a detection position with a driver for distance control 5. A plastic scintillation fiber scope 2 is fixed inside a distance control plate 3, both sides of it are connected to a time wave height converter 7 to detect light from left and right directions, and from the time difference, the detection position of radioactivity is obtained. Then, the amount is measured with a radioactivity meter 8 and a gate monitor 4 is operated with a personal computer 9. When it is below a certain value, a gate in outlet side is made available of going out, and when above a certain value, a gate in inlet side is opened and contamination location is specified, decontaminated and reinspected. The scintillation fiber scope 2 has a length of ca. 10 m so that one scope can measure one turn or more and can be bent and by making access to a measuring object to attain efficient measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radioactivity measuring device.

[0002]

2. Description of the Related Art Conventionally, in a facility handling radioactive materials such as a nuclear power plant, a radioactivity measuring instrument is installed in order to measure radioactive contamination of workers and articles carried out.

[0003] As an example, a gate monitor used for monitoring a worker leaving a controlled area in a nuclear power plant will be described. In FIG. 2, 1 is a person to be measured, 4 is a gate monitor, and 20 is a sensor for gate monitoring. When a worker who works in a facility handling radioactive materials leaves the general area, enter the gate monitor in 4 and measure radioactivity for a certain period of time to confirm that there is no radioactive material. First, open the door, enter the gate monitor, switch on the measurement with your own hand, and measure for a certain period of time. The gate monitor comprises a plurality of radioactivity detectors as shown at 20. These detectors usually use a plastic scintillator having a diameter of several tens. A plastic scintillator can be made relatively inexpensive and a large detector can be manufactured, maintenance is easy, detection efficiency is relatively high, and measurement can be performed in a short time of 10 to 20 seconds. Open the door on the control area side, enter the gate monitor and measure. If it is below a certain value, you can leave the control area as it is. However, if the value is above a certain value, the door on the control area side opens again without opening the door on the exit side, confirming the contaminated area on the monitor, and cleaning the hand, foot, head, etc. that is the area using a detergent. Measure again. This operation is repeated until the value falls below a certain value. The gate monitor must determine if there is contamination for the operator in as short a time as possible. For this purpose, plastic scintillators, which are large detectors, are used, but they may be contaminated with radioactive substances depending on how they are handled.
After contamination, radioactive materials need to be removed from time to time due to high background. First, remove the contamination prevention cover and check if any contamination remains. The BG can be returned to the original BG by replacing the contamination prevention cover, but in some cases, the measurement sensor may be contaminated. At that time, the surface of the sensor is carefully decontaminated, but sometimes it is damaged and needs to be replaced. After exchanging the detectors, several types of nuclides are measured using a model called a phantom containing a radioactive substance simulating the human body, and a calibration constant is obtained. If the detector is contaminated in this way, it often takes a few days to recover. Nuclear power plants are divided into three or four stages according to the level of radioactive contamination in radiation management. This is because a barrier is formed depending on the level of the surface contamination to minimize the spread of the contamination. Usually, it is performed at the stages of A, B, C, and D, and the contamination level increases from A to D.

When transferring the tool used in D to C,
Measure the contamination with a contamination monitor such as a survey meter, and confirm that it is below the standard. If there is contamination above the standard, decontaminate and measure again to confirm that it is below the standard level. Furthermore, when decontamination is difficult, stop taking out and manage it exclusively for the contaminated area.

As described above, measurement between various levels requires measurement of various road tools. Therefore, it takes time, but a survey meter or the like is mainly used, and a contamination monitor or the like that can be automatically measured is not used.

[0006]

The above prior art is a measuring method using a detector having a certain size and shape.
The efficiency of the measuring device has been reduced for a substance having a complicated shape or an operator having an extremely different physique. Also, it took time to start decontamination and remeasurement when the detector was contaminated.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to use a detector using a plastic scintillation fiberscope and its detector in place of the one used for the detector of the detector. Can be solved.

[0008] The plastic scintillation fiberscope is formed by coating stainless steel on the outside of a thin plastic wire, and can be used by being bent to some extent, so that the object can be measured efficiently by approaching the object to be measured.

[0009] Plastic scintillation fiberscopes emit light in both directions when exposed to radioactivity. By putting this light into a time-height analyzer, the position where the radiation has hit can be determined. Since this sensor can be used by bending, it can be measured by an operator or a measurement object having a complicated shape.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a worker who is a subject.
2 is a plastic scintillation fiberscope which is a sensor for measuring radioactivity, 3 is a distance adjusting plate of a gate monitor, 4 is an outer frame of a gate monitor, 5 is a driving device for a distance adjusting plate, 6 is a distance measuring sensor, and 7 is a TAC. A time wave height converter, 8 is a radioactivity measuring instrument, and 9 is a personal computer for driving a gate monitor.

First, an operator 1 who is going to undergo a contamination test
Goes into the gate monitor of 4. When it enters, switch on the measurement. As a result, the adjustment plate driving device operates at the distance of 5, and moves to the position detected by the distance measuring sensor of 6. The person to be measured corresponds to various people such as physique and height, but the distance adjustment plate moves according to each,
Stop as close as possible. If the distance adjustment plate approaches and comes into contact extremely, the measurement sensor is contaminated, and since the subject has a feeling of pressure, the measurement is performed to the extent that the contact does not come into contact. A plastic scintillation fiberscope for radioactivity measurement 2 is attached inside the distance adjusting plate 3. Since the plastic scintillation fiberscope can be bent at a radius of about 10, a loop can be formed at each corner as shown in the figure, and measurement can be performed with a single fiber. Since the plastic scintillation fiberscope can bend even when the distance adjusting plate of No. 3 comes close to the subject, it can be measured by one. Both ends of the plastic scintillation fiberscope are connected to 7 time-to-peak converters. Here, the light from the right direction and the light from the left direction are detected,
The position at which the radioactivity is detected can be obtained from the time difference. That is, the plastic scintillation fiberscope receiving the radioactivity at a position close to the distance measuring sensor 6 emits light and goes downward to the time wave converter 7 and also goes upward to pass through the head part and the other side part 7. Time to reach the wave height converter. As described above, a time difference occurs depending on the traveling route, and thus, the position receiving the radiation can be obtained. After that, the quantity is measured by the radioactivity measuring instrument 8 and the gate monitor is operated by the personal computer 9. If it is below a certain value, the exit gate can be opened to exit, and if it is above a certain value, the entrance side gate opens, so the contaminated area is checked, decontaminated, and inspected again. Since the plastic scintillation fiberscope has a length of about 10 m, one circumference can be measured by one, and it can be bent, so that it can be efficiently measured as close to the object as possible. Even if the plastic scintillation fiberscope is contaminated, it can be easily decontaminated because it is covered with stainless steel. In FIG. 1, if a plurality of plastic scintillation fiberscopes are installed in the depth direction, the radioactivity can be measured efficiently. In FIG. 1, a person to be measured is described as a person to be measured, but a contaminated article such as a pipe or a steel material can be efficiently measured by the same method.
If the measurement is performed by moving the sensor as close as possible to the object to be measured, the measurement is completed in a short time. In addition, even an object having a complicated shape can be measured without the risk of the measurement sensor being damaged, and can be used for movement measurement between positions having different management divisions.

[0012]

According to the present invention, a radioactivity measuring instrument which can be measured efficiently and in a short time by approaching an operator, which has been difficult in the past, becomes possible, and a radioactivity measuring instrument which is easy to decontaminate when contamination occurs. Can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a gate monitor according to the present invention.

FIG. 2 is an explanatory diagram of a gate monitor according to a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Worker who is a to-be-measured person 2 ... Plastic scintillation fiberscope 3 ... Distance adjustment plate of a gate monitor 4 ... Outer frame of a gate monitor 5 ... Driving device for distance adjustment 6 ... Distance measuring sensor 7 ... Time Wave height converter (TA
C), 8: Radioactivity measuring instrument, 9: PC for driving gate monitor, 20: Radioactivity measuring sensor.

Claims (3)

[Claims] 1. A radioactivity measuring apparatus characterized in that a plastic scintillation fiberscope is used as a sensor of a monitor for leaving a controlled area. 2. A radioactivity measuring apparatus according to claim 1, further comprising a mechanism for allowing said plastic scintillation fiberscope to approach an object to be measured, and a sensor for detecting a position. 3. An apparatus for measuring radioactivity, wherein when an article is moved between locations having different management divisions, the article is measured by a radioactivity measuring apparatus using a plastic scintillation fiberscope.