JP2006090963A - Radioactive dust monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a radiation dose in radioactive dust included in sampling air, and simultaneously to detect a radiation dose in a gaseous radioactive material included in the sampling air, concerning a radioactive dust monitor. <P>SOLUTION: In a sampling vessel 1, a filter paper 4 for capturing dust in the sampling air by passage of the sampling air, and a gas adsorbent 8 for adsorbing radioactive gas in the sampling air by passage of the sampling air are provided, and a radiation detector 2 for detecting each radiation dose in the dust and the radioactive gas captured and adsorbed respectively is also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radioactive dust monitor that continuously measures and monitors the concentration of radioactive substances in the air to monitor air pollution by radioactive substances.

  In radioactive material handling facilities such as nuclear power plants, nuclear fuel handling facilities, and hospitals, the radiation dose in the work environment is set for the purpose of radiation protection for workers or to monitor leakage of radioactive materials in the facility. Various types of radiation monitoring devices are provided to measure and determine the results and link them to radiation protection measures.

  Among these radiation monitoring devices, a radioactive dust monitor has been used to monitor air pollution by radioactive materials by attaching filter paper, capturing dust floating in the air with this filter paper, and measuring the radiation dose of this dust. in use.

FIG. 6 shows the structure of a conventional radioactive dust monitor. In FIG. 6, 1 is a sampling container formed of a sealed container, 2 is a radiation detector supported and fixed in the sampling container 1 by a support member 3,
A filter paper 4 is provided so as to face the detection surface 2a of the radiation detector 2 at an appropriate interval, and is held in the sampling container 1 so that the upper and lower edges are sandwiched between the filter paper holders 5a and 5b. The support is fixed.

  6a and 6b are sampling air introduction and discharge pipes. An introduction pipe 6a is provided on the detector side of the filter paper 4 so as to communicate with the inside of the sampling container 1. The other side of the filter paper 4 communicates with the inside of the sampling container 1. In this way, the discharge pipe 6b is provided, and sampling air containing dust floating in the surrounding work environment is introduced into the sampling container 1 through the introduction pipe 6a by the action of a circulation pump (not shown).

  Reference numeral 7 denotes a cable that connects the radiation detector 2 and a control device provided outside (not shown), transmits a detection signal of the radiation detector 2 to the control device, and supplies power to the radiation detector 2 from the control device. To do.

Next, the operation of the radioactive dust monitor configured as described above will be described.
Sampling air in the working environment is drawn into the sampling container 1 through the introduction pipe 6a by a circulation pump (not shown), and flows through the sampling container 1 as indicated by an arrow X to forcibly pass the filter paper 4.

When the sampling air passes through the filter paper 4, dust contained in the sampling air is captured by the filter paper 4.
The sampling air that has passed through the filter paper 4 is again discharged into the working environment outside the sampling container 1 through the discharge pipe 6b.

The dust captured by the filter paper 4 is measured for the concentration of the radioactive substance by the radiation detector 2 provided opposite to the filter paper 4, and the detection signal is sent to an external control circuit via the cable 7. Signal processing is performed.
The processed signal is evaluated for safety by comparing the detection result with the radiation dose limit value, etc., and linked to necessary measures for radiation protection such as improvement of the facility working method.

  As described above, the conventional radioactive dust monitor is used for the purpose of capturing dust in sampling air, measuring the radiation dose, and preventing the intake of radioactive substances due to the respiration of radiation workers.

  On the other hand, in nuclear power generation facilities and the like, there is a possibility that minute steam leaks from the piping and joints in the site, and there is a demand for monitoring the radioactive gas (such as sodium 13) contained in the leaked steam with high sensitivity. is there.

  As a method of measuring radioactive gas (sodium 13 or the like) with a dust monitor, although it is mentioned as a phosucci detector as an application (see, for example, Patent Document 1), a specific gas measuring method is mentioned. The invention is not seen.

Regarding the measurement related to sodium 13, for example, there is a method of removing as in Patent Document 2, but a method of positive measurement is not seen.
It is also conceivable to simultaneously count 511 keV pair annihilation γ-rays due to positrons emitted by sodium 13, for example, as described in Patent Document 3, β / γ discrimination for radon suppression, for example, Patent Document 4 Only inventions such as coincidence of output between the radiation measuring device and another device can be seen, and no method of positively utilizing the pair annihilation gamma rays due to the positrons of sodium 13 is found.
Japanese Patent Laid-Open No. 5-341047 JP 11-311676 A Japanese Patent Laid-Open No. 11-64529 JP-A-7-333349

  As described above, in the conventional radioactive dust monitor, dust is introduced into the sampling container 1 and captured by using the filter paper 4, so that the dust contained in the sampling air can be captured with high sensitivity and efficiency. Although it is possible to reliably measure the radiation dose of the radioactive material in the dust, it was difficult to detect with high sensitivity to the gaseous radioactive material contained in the sampling air.

  The present invention has been made to solve the above problems, and can detect not only dusty radioactive substances contained in the air but also gaseous radioactive substances contained in the air with high sensitivity and efficiency. An object is to provide a radioactive dust monitor.

  In order to achieve the above object, the radioactive dust monitor according to the present invention includes a sampling container into which sampling air is introduced, and a sampling container provided in the sampling container and passing through the sampling air introduced into the sampling container. A filter paper that captures dust in the air, a gas adsorbent that is provided in the sampling container and that adsorbs radioactive gas in the sampling air by passing the sampling air introduced into the sampling container, and the sampling container It is provided inside, and consists of the radiation detector which detects the radiation dose of the radioactive gas captured and adsorbed by the filter paper and the gas adsorbent.

  According to the radioactive dust monitor of the present invention, not only dusty radioactive substances contained in the air but also gaseous radioactive substances contained in the air can be detected with high sensitivity and efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiment, the same parts as those in the conventional radioactive dust monitor shown in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1, 1 is a sampling container, 2 is a radiation detector, 4 is filter paper, 6a is an introduction tube, and 6b is a discharge tube.
Reference numeral 8 denotes a gas adsorbent using activated carbon, which has a plate shape and is supported in the sampling container 1 by the support members 9a and 9b at an appropriate interval from the filter paper 4 on the downstream side of the sampling air flow of the filter paper 4. It is fixed.

  In the case of the radioactive dust monitor having such a configuration, the sampling air drawn into the sampling container 1 from the introduction pipe 6a flows through the sampling container 1 as indicated by the arrow X, and is forced to pass through the filter paper 4 and the gas adsorbent 8. And is discharged again from the discharge pipe 6b into the work environment.

The radioactive dust contained in the sampling air is captured on the surface of the filter paper 4 with a high probability, and the radiation emitted therefrom is detected by the radiation detector 2.
At this time, by shortening the distance between the radiation detector 2 and the filter paper 4, the radiation detector 2 is sufficiently suppressed in the attenuation of radioactivity with weak transmission power, for example, α rays and β rays. Can be detected.

  On the other hand, although the gaseous radioactive substance is difficult to be captured by the filter paper 4, after passing through the filter paper 4, it is adsorbed and captured by the gas adsorbent 8 provided on the downstream side of the filter paper 4, and the radioactive substance is removed by the radiation detector 2. Detected.

In particular, leakage detection of sodium 13 measures 511 keV γ-rays due to the annihilation of positrons emitted from sodium 13, but this radiation has a penetrating power compared to the α-rays and β-rays described above. Strongly attenuated by the gas in the space up to the radiation detector 2 and the filter paper 4, and further by self-shielding by the gas adsorbent 8 itself, and is not so great, even though it is arranged downstream of such filter paper 4 The radiation detector 2 can detect with good probability.
As described above, according to the radioactive dust monitor according to the present embodiment, not only detection of radioactive dust in the air but also detection of radioactive gas in the air can be performed with high sensitivity.

  Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, 8 is a gas adsorbent similar to that described in the first embodiment, and is applied to the surface of the filter paper 4 facing the downstream side of the sampling air flow.

According to the present embodiment, since it is not necessary to support and fix the gas adsorbent plate in the sampling container 1 using the support member, the structure becomes simple and the assembly becomes easy.
Further, if the gas adsorbent 8 is applied to the filter paper 4 in advance, the assembly becomes even easier.

  Furthermore, when the gas adsorbent 8 is applied to the surface of the filter paper 4 facing the upstream side of the sampling air flow, the adsorbed radioactive dust moves under the activated carbon so that the permeability is weakened by the activated carbon. Although the detection sensitivity of radioactive dust that is shielded by radiation is lowered, the detection sensitivity can be prevented from lowering by applying activated carbon to the downstream surface of the filter paper 4.

  Next, a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, reference numeral 10 denotes a plurality of gas adsorbents formed in a pellet shape, sandwiched between two filter papers 4a and 4b with a space between each other, and a sampling container by the filter paper holders 5a and 5b. 1 is supported and fixed inside.

  According to the present embodiment, the gas adsorbent 8 is formed in a pellet form and is sandwiched between the two filter papers 4a and 4b with a space between each other. The pressure loss due to the gas adsorbent 8 can be reduced, and the capacity of the circulation pump for sampling air suction can be reduced.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 4, reference numeral 10 denotes a plurality of gas adsorbents formed in the form of pellets on a surface facing the downstream side of the sampling air flow of the filter paper 4 supported and fixed in the sampling container 1 by the filter paper holders 5a and 5b. It is pasted at intervals.

According to the present embodiment, since it is not necessary to support and fix the gas adsorbent plate in the sampling container 1 using the support member, the structure becomes simple and the assembly becomes easy.
In addition, since the gas adsorbent 8 is formed in a pellet shape and attached at intervals, the gas adsorbent 8 does not block all the sampling air flow paths, and pressure loss due to the gas adsorbent 8 is reduced. The capacity of the circulating pump for sampling air suction can be reduced.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In FIG. 5, 11 is a gamma ray detector provided in the sampling container 1, and is provided downstream of the flow of sampling air of the gas adsorbent 8 in the first embodiment.
Reference numeral 12 denotes a simultaneity determination device that determines the simultaneity of the outputs of the radiation detector 2 and the γ-ray detector 11, and 13 denotes a simultaneity counting device that counts the output of the simultaneity determination device 12.

In general, a positron emitting nuclide such as sodium 13 emits a positron, and when the positron annihilates, two 511 keV γ rays are emitted in opposite directions.
Therefore, if the solid angle from the position of positron annihilation is the same in the radiation detector 2 and the γ-ray detector 11, radiation detection can be performed by ignoring the shielding effect by air and objects until the incidence of γ-rays. When γ-rays due to pair annihilation enter the detector 2, another γ-ray due to pair annihilation also enters the opposite γ-ray detector 11, and the coincidence of both is calculated by the amount of positron emitting nuclides present. Has a strong correlation.

If the solid angle is different between the two and considering the shielding effect between them, the probability that radiation will be incident on both detectors and coincidence will have a strong correlation with the abundance of positron nuclides. .
On the other hand, the background gamma rays incident from the outside are unlikely to enter both detectors simultaneously.

According to the present embodiment, it is possible to measure a radioactive gas that is a positron emitting nuclide while reducing the influence of an external background.
Further, in the conventional configuration, the normal radioactive dust has a long half-life, and in the case of sodium 13, the half-life is as short as 9.96 minutes, so it was difficult to correct the half-life. Therefore, accurate half-life correction is possible.

  Next, a sixth embodiment of the present invention will be described. As the radiation detector 2 described in the first to fifth embodiments, a radiation detector capable of discriminating the line type of incident radiation can be used.

  As such a detector, for example, a foswitch type detector in which a ZnS (Ag) layer is bonded to the incident surface side and a plastic scintillator is bonded to the back of the detector and the optical sensor is coupled.

For example, in such a foswitch type sensor, the output waveform due to the interaction of radiation with ZnS (Ag) and the output waveform due to the interaction of radiation with the plastic scintillator are different. Incidence of weak radiation has an output waveform component due to ZnS (Ag), and radiation with a slight transmission power such as β rays and radiation with a large transmission power such as γ rays mainly has an output waveform component due to plastic scintillators. become.
In this case, the α-ray component of radioactive dust captured on the filter paper 4 can be separated from other components.

  Furthermore, by adjusting the thickness of the plastic scintillator appropriately and further placing a scintillator with a sufficient thickness having another output waveform component between it and the optical sensor, the waveform due to the incidence of γ rays is mainly the third. The output waveform component of the scintillator can be provided.

  In this way, the α-ray component of the radioactive dust captured on the filter paper 4, the β-ray component of the radioactive dust repaired on the filter paper 4, the radioactive dust captured on the filter paper 4 and the activated carbon gas adsorbent 8 are captured. Can be distinguished from the γ-ray component of the radioactive gas.

  Further, in the coincidence counting of the fifth embodiment, by acquiring the simultaneity between the γ-ray component and the γ-ray detector 11, the amount of positron emitting nuclides such as sodium 13 in the γ-ray component is discriminated. be able to.

  According to the present embodiment, it is possible to discriminate the radiation of captured radioactive dust and radioactive gas, and obtain the concentrations of radioactive dust and radioactive gas in the air for each radiation line type.

Next, a seventh embodiment of the present invention will be described.
In the fifth embodiment, a radiation detector capable of obtaining radiation energy information can be used as the radiation detector 2 and the γ-ray detector 11.
By taking such a configuration, an energy spectrum of incident radiation can be obtained.

Under such a configuration, the radiation detector 2 and the γ-ray detector 5 perform radioactivity determination, which is a positron emitting nuclide, by determining the synchronism of outputs only in a range corresponding to the incidence of 511 keV γ-rays. A high-performance dust monitor capable of measuring gas can be obtained.
In the description of the embodiment, the activated carbon adsorbent is used as the gas adsorbent, but other adsorbents other than the activated carbon adsorbent may be used.

Sectional drawing which shows the radioactive dust monitor by the 1st Embodiment of this invention. Sectional drawing which shows the radioactive dust monitor by the 2nd Embodiment of this invention. Sectional drawing which shows the radioactive dust monitor by the 3rd Embodiment of this invention. Sectional drawing which shows the radioactive dust monitor by the 4th Embodiment of this invention. Sectional drawing which shows the radioactive dust monitor by the 5th Embodiment of this invention. Sectional drawing which shows the conventional radioactive dust monitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sampling container, 2 ... Radiation detector, 3 ... Support member, 4 ... Filter paper, 5a, 5b ... Filter paper holder, 6a ... Introduction pipe, 6b ... Discharge pipe, 7 ... Cable, 8 ... Gas adsorption material, 9a, 9b DESCRIPTION OF SYMBOLS ... Supporting member, 10 ... Gas adsorbent pellet, 11 ... Gamma ray detector, 12 ... Simultaneous determination device, 13 ... Simultaneous counting device

Claims (8)

  A sampling container into which sampling air is introduced, a filter paper which is provided in the sampling container and captures dust in the sampling air by passing the sampling air introduced into the sampling container, and provided in the sampling container A gas adsorbent that adsorbs the radioactive gas in the sampling air when the sampling air introduced into the sampling container passes, and is trapped and adsorbed in the filter paper and the gas adsorbent provided in the sampling container A radioactive dust monitor comprising: a dust detector and a radiation detector for detecting a radiation dose of the radioactive gas.   The radioactive dust monitor according to claim 1, wherein the gas adsorbent is disposed on the downstream side of the sampling air flow of the filter paper.   2. The radioactive dust monitor according to claim 1, wherein a gas adsorbent is applied to a surface of the filter paper facing the downstream side of the sampling air flow.   2. The radioactive dust monitor according to claim 1, wherein the gas adsorbing material is sandwiched between two filter papers.   The radioactive dust monitor according to claim 1, wherein a gas adsorbent is attached to a surface of the filter paper facing the downstream side of the sampling air flow.   6. The radioactive dust monitor according to claim 1, wherein a radiation detector capable of discriminating incident ray types is used as the radiation detector.   The radioactive dust monitor according to claim 1, wherein a γ-ray detector is disposed on the downstream side of the flow of sampling air of the gas adsorbent. 8. The radioactive dust monitor according to claim 7, wherein a detector capable of energy discrimination of incident radiation is used as the gamma ray detector.

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