JPH06214034A - Dust radiation monitor - Google Patents

Abstract

(57) [Abstract] [Object] The present invention provides a monitor capable of detecting a stable and reliable detection of a process pipe leak by removing a radioactivity concentration which is an obstacle other than a nuclide to be measured for a dust radioactivity concentration. [Constitution] β released from the radioactivity collected on the filter paper (11)
Rays are detected by the β ray detector (20), and γ rays are detected by the γ ray detector (2
1), of which the output pulses of the β-ray detector (20) are counted by the β-ray dust concentration measurement unit (22) to obtain the dust radioactivity concentration, and the output of the γ-ray detector is determined by the nuclide analysis unit. Obtain the interfering radioactivity concentration against the dust radioactivity concentration by counting according to (23). Then, the dust radioactivity concentration is corrected by the measurement interfering nuclide component correction unit (24) using the interfering radioactivity concentration to obtain the dust radioactivity concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust radiation monitor for measuring a dust radioactivity concentration in a nuclear facility.

[0002]

2. Description of the Related Art FIG. 8 is an overall configuration diagram of a dust radiation monitor. A room 1 in a nuclear facility is surrounded by a wall 2 made of concrete. A process pipe 3 is arranged in the room 1. Further, a ventilation plug 4 is provided in the room 1, a ventilation duct 5 is connected to the ventilation plug 4, and the air in the room 1 is exhausted from the stack 7 by the air exhaust action of the air exhauster 6.
To be sent to.

On the other hand, a sampling tube 8 for a dust monitor is arranged in the room 1, and the sampling tube 8 is connected to a dust radiation monitor 9 and further communicates with a ventilation duct 5. Then, the air in the room 1 is sucked by the sampling pump (suction pump) 10 provided in the sampling pipe 8 and sent to the ventilation duct 5.

As shown in FIG. 9, this dust radiation monitor 9 has a filter paper 11 arranged in a sampling tube 8 and a β ray detector 12 installed above the filter paper 11. As a result, the sampled air in the room 1 passes through the filter paper 11, and at this time, dust contaminated by radioactivity in the air is collected on the filter paper 11.

Therefore, the β-ray detector 12 detects all β-rays emitted from the radioactivity collected on the filter paper 11. The measuring unit 13 counts the output pulses of the β-ray detector 12, and subtracts the count rate (background count rate: BG count rate) when the radioactivity is not collected to obtain the true dust radioactivity concentration. calculate. Then, the dust radioactivity concentration is instructed by the instruction unit 14.

Here, the radioactivity to be measured in the air of the room 1 of the nuclear facility is the rare gas ( ⁸⁸ Kr, leaked from the process pipe 3). ¹³⁸ Xe) daughter nuclide ( ⁸⁸ Rb, ¹³⁸ C
s) etc.

However, in the room 1 of the nuclear facility
This noble gas (⁸⁸Kr, ¹³⁸X
e) daughter nuclide (⁸⁸Rb, ¹³⁸Cs), etc.
Nuclide (⁶⁰Co,⁵⁴Mn) and released from the wall 2
²²²Rn daughter nuclide group ( ²¹⁴Po, ²¹⁴Nuclides such as Pb)
It is included.

Since these nuclides emit β rays,
²²² Rn daughter nuclide ( ⁸⁸ Rb, It is an interfering nuclide in measurement because it is difficult to separate it from ¹³⁸ Cs). further,
This is a disturbing nuclide ²²² Rn daughter nuclide group ( ²¹⁴ Po,
²¹⁴ Pb, etc.) fluctuates according to the operation of ventilation in the room 1 of the nuclear facility, the weather, the time, etc., so the level rises and it is judged that the leak has accidentally occurred, although no pipe leak has occurred. Sometimes.

[0009]

As described above, the dust radioactivity concentration is an interfering nuclide. ²²² Rn daughter nuclide group (
²¹⁴ Po, ²¹⁴ Pb, etc.) is included, which causes an error in measurement of dust radioactivity concentration.

Therefore, an object of the present invention is to provide a dust radiation monitor capable of removing the interfering nuclide component of the dust radioactivity concentration and detecting the leak in the process pipe in a stable and reliable manner.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a dust radiation monitor for sampling a gas, passing it through a filter paper, and detecting the radioactive radiation collected on the filter paper to measure the dust activity concentration.

Β released from the radioactivity collected on the filter paper
Beta-ray detector that detects X-rays, γ-ray detector that detects γ-rays emitted from the radioactivity trapped on the filter paper, and the output of the β-ray detector is counted to obtain the dust radioactivity concentration Dust Concentration measuring means, nuclide analysis means for counting the output of the γ-ray detector to obtain the interfering radioactivity concentration with respect to the dust radioactivity concentration,
A dust radiation monitor, which is provided with a correction unit that corrects the dust radioactivity concentration obtained by the dust concentration measurement unit with an interfering radioactivity concentration, to achieve the above object.

[0013]

By providing such means, β rays emitted from the radioactivity collected on the filter paper can be detected by the β ray detector and γ rays can be detected by the γ ray detector. The output of the ray detector is counted by the dust concentration measuring means to obtain the dust radioactivity concentration, and the output of the γ ray detector is counted by the nuclide analysis means to obtain the interfering radioactivity concentration with respect to the dust radioactivity concentration. Then, the dust radioactivity concentration is corrected by the interfering radioactivity concentration by the correcting means to obtain the dust radioactivity concentration from which the variable element is removed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. The same parts as those in FIG. 8 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a block diagram of a dust radiation monitor applied to a room in a nuclear facility. Beta above the filter paper 11
A ray detector 20 is arranged, and a γ ray detector 21 is arranged below the filter paper 11. These detectors 20, 21
The β-ray detector 20 includes a β-ray dust concentration measuring unit 22
, And the nuclide analysis unit 23 is connected to the γ-ray detector 21.

The β-ray dust concentration measuring unit 22 operates in accordance with the dust concentration measuring flow chart shown in FIG. 2, and obtains the BG count rate when radioactivity is not trapped on the filter paper 11 in advance to detect β-rays. It has a function of counting the pulses higher than the discrimination setting value among the output pulses of the container 20, and subtracting the BG counting rate from this counting rate to obtain the dust radioactivity concentration.

The nuclide analyzing section 23 operates in accordance with the flow chart for measuring interfering radioactivity shown in FIG. 3, counts the output pulses of the γ-ray detector 21, and photoelectrically converts it into a peak value corresponding to the γ-ray energy as the interfering nuclide. It has a function of monitoring whether a peak is generated and, if a photoelectric peak is generated, obtaining the interfering radioactivity concentration from the peak area.

Further, the measurement interfering nuclide component correction unit 24 subtracts and corrects the interfering radioactivity concentration obtained by the nuclide analysis unit 23 from the dust radioactivity concentration obtained by the β-ray dust concentration measuring unit 22 to correct the interfering nuclide. It has the function of obtaining the dust radioactivity concentration after removing the fluctuation factors. Next, the operation of the monitor configured as described above will be described.

When the filter paper 11 is placed in the sampling tube 8, the β-ray detector 20 detects that the filter paper 11 does not collect radioactivity.
The β rays emitted from the sensor are detected and a pulse is output accordingly. In this state, the β-ray dust concentration measuring unit 22 counts the pulses output from the β-ray detector 20 in step # 1 of FIG. 2 to obtain the BG count rate.

Next, the air in the room 1 sampled by the operation of the sampling pump 10 passes through the filter paper 11, at which time dust contaminated by radioactivity in the air is filtered by the filter paper 1.
Collected in 1.

In this state, the β-ray detector 20 detects all β-rays emitted from the radioactivity collected on the filter paper 11 and outputs a pulse corresponding thereto. In this case, since the β ray does not have a single energy, the output wave height distribution of the β ray detector 20 is as shown in FIG.

The β-ray dust concentration measuring unit 22 counts the pulses (A portion and B portion) higher than the discrimination setting value Q shown in FIG. 4 among the pulses output from the β-ray detector 20 in step # 2. To do. The B portion is the BG count rate.

Next, the β-ray dust concentration measuring unit 22 obtains the count rate (NET count rate) of the A portion by subtracting the BG count rate from the pulse count rate higher than the discrimination setting value Q in step # 3. , And this is multiplied by the coefficient K to obtain the dust radioactivity concentration S. When obtaining the dust radioactivity concentration, not only the coefficient K is multiplied, but a half-life correction may be added. The dust radioactivity concentration S is an interfering nuclide. ²²² Rn daughter nuclide group ( ²¹⁴ Po, ²¹⁴ Pb
Etc.) concentration is also included.

Next, the β-ray dust concentration measuring unit 22 determines in step # 4 whether the dust radioactivity concentration has been measured n times, and if it is determined n times, the filter paper 11 is replaced with a new one.

On the other hand, the γ-ray detector 21 detects all γ-rays emitted from the radioactivity collected on the filter paper 11. In this case, the output wave height distribution of the γ-ray detector 21 is as shown in FIG.

In step # 10, the nuclide analyzing section 23 counts the pulses (A 'portion, B'portion and C'portion) corresponding to the γ-ray energy as the interfering nuclide among the output pulses of the γ-ray detector 21. Then, in the next step # 11, it is monitored whether or not a photoelectric peak occurs at the peak value corresponding to the γ-ray energy.

If a photopeak has been generated by monitoring this photopeak, the nuclide analyzing section 23 obtains the peak area A'in step # 12, and then the next step # 13.
In step S, the interfering activity concentration S ′ is obtained.

Next, the measurement interfering nuclide component correcting unit 24 uses the dust radioactivity concentration S determined by the β-ray dust concentration measuring unit 22 to determine the interfering radioactivity concentration S'determined by the nuclide analyzing unit 23.
Is subtracted and corrected to obtain the dust radioactivity concentration with the variable elements of the interfering nuclide removed. Then, the dust radioactivity concentration is instructed to the instruction unit 14.

As described above, in the first embodiment, the β ray emitted from the radioactivity collected on the filter paper 11 is detected by the β ray detector 20 to obtain the dust radioactivity concentration, while the γ ray is emitted. Is detected by the γ-ray detector 21 to obtain the interfering radioactivity concentration, and the dust radioactivity concentration is corrected by the interfering radioactivity concentration to obtain the dust radioactivity concentration with the variable elements removed. is there ²²² Rn daughter nuclide group ( ²¹⁴ Po, An accurate dust radioactivity concentration can be obtained by removing the concentration of ²¹⁴ Pb). This allows
Whether the dust radioactivity concentration has increased due to a leak in the plant pipe 3 or due to fluctuations in interfering nuclides can be reliably detected, and only a plant abnormality can be reliably detected and dealt with. Next, a second embodiment of the present invention will be described. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 6 is a block diagram of the dust radiation monitor. The β-ray detector 20 is arranged inside the sampling tube 8, and the γ-ray detector 21 is arranged outside the sampling tube 8.

Between the β-ray detector 20 and the γ-ray detector 21, each roller 31 of the filter paper transport mechanism 30 is arranged, and a filter paper cutting mechanism 32 is provided between the rollers 31.

The control device 33 controls the operations of the filter paper transport mechanism 30 and the filter paper cutting mechanism 32, and calculates the β-ray dust concentration measuring unit 22, various analyzing units 23, and measurement disturbing nuclide component correcting unit 24. It has the function of controlling the timing. Next, the operation of the monitor configured as described above will be described with reference to the dust concentration measurement flow chart shown in FIG.

The controller 33 sends a filter paper supply command to the filter paper transport mechanism 30 in step # 20. As a result, the filter paper transport mechanism 30 arranges the filter paper 11 in the sampling tube 8 below the β-ray detector 20. Next, the control device 33 sends a measurement command to the β-ray dust concentration measuring unit 22 in step # 21.

The β-ray dust concentration measuring unit 22 counts the pulses higher than the discrimination setting value Q among the pulses output from the β-ray detector 20 as described above, and based on this counting rate, B
The NET count rate is obtained by subtracting the G count rate, and this is multiplied by the coefficient K to obtain the dust radioactivity concentration S. The BG count rate is obtained in advance as in the first embodiment.

Next, the controller 33 issues a cutting command to the filter paper cutting mechanism 32 in step # 22, and then issues a transportation command to the filter paper transportation mechanism 30 in step # 23. As a result, the filter paper cutting mechanism 32 cuts the filter paper 11, and then the control device 33 conveys the filter paper 11 and arranges it above the γ-ray detector 21.

Next, the control unit 33 controls the steps # 24, #.
25, a measurement command is issued to the nuclide analysis unit 23. Similarly to the above, the nuclide analysis unit 23 counts the pulses corresponding to the γ-ray energy that becomes the interfering nuclide among the output pulses of the γ-ray detector 21, and monitors whether a photoelectric peak is generated, and this photoelectric peak generation is performed. If so, the interfering radioactivity concentration S ′ is obtained from the peak area A ′.

Next, the control device 33 issues a correction command to the measurement interference nuclide component correction unit 24 in step # 26.
The measurement interfering nuclide component correction unit 24 subtracts the interfering radioactivity concentration S ′ obtained by the nuclide analysis unit 23 from the dust radioactivity concentration S obtained by the β-ray dust concentration measuring unit 22 and corrects the interfering nuclide variation. The dust radioactivity concentration with the elements removed is determined, and this is instructed to the instruction unit 14.

As described above, according to the second embodiment, the same effect as that of the first embodiment can be obtained, and the structure of the dust collecting portion for disposing the filter paper 11 in the sampling tube 8 can be simplified.

The present invention is not limited to the above-mentioned embodiments, but may be modified without departing from the scope of the invention. For example, the modification may be made within the range without departing from the gist of measuring both β-rays and γ-rays and removing the interfering component obtained from the γ-ray nuclide analysis result from the β-ray measurement result.

[0040]

As described above in detail, according to the present invention, it is possible to provide a dust radiation monitor capable of removing the measurement error due to the interfering radionuclide radioactivity of the dust radioactivity concentration and stably and surely detecting the process pipe leak.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a dust radiation monitor according to the present invention.

FIG. 2 is a flowchart of dust concentration measurement in the radiation monitor.

FIG. 3 is a flow chart of interfering radioactivity measurement in the radiation monitor.

FIG. 4 is an output wave height distribution diagram of a β-ray detector in the radiation monitor.

FIG. 5 is an output wave height distribution diagram of a γ-ray detector in the radiation monitor.

FIG. 6 is a configuration diagram showing a second embodiment of the dust radiation monitor according to the present invention.

FIG. 7 is a flowchart of dust concentration measurement in the radiation monitor.

FIG. 8 is a configuration diagram of a nuclear facility to which the radiation monitor is applied.

FIG. 9 is a configuration diagram of a conventional dust radiation monitor.

[Explanation of symbols]

1 ... Room in nuclear facility, 2 ... Wall, 3 ... Process piping, 4
… Ventilation plug, 5… Ventilation duct, 6… Exhaust fan, 7… Stack, 8… Sampling tube, 10… Sampling pump,
11 ... Filter paper, 20 ... β-ray detector, 21 ... γ-ray detector, 2
2 ... β-dust concentration measuring unit, 23 ... Nuclide analyzing unit, 24
... Measurement interference nuclide component correction unit, 30 ... Filter paper transport mechanism, 31
... roller, 32 ... filter paper cutting mechanism, 33 ... control device.

Claims (1)

[Claims] 1. A dust radiation monitor for measuring a dust radioactivity concentration by sampling a gas, passing it through a filter paper, detecting the radiation of the radioactivity trapped on the filter paper, and collecting the radioactivity trapped on the filter paper. A β-ray detector for detecting β-rays emitted from the detector, a γ-ray detector for detecting γ-rays emitted from the radioactivity trapped on the filter paper, and counting the output of the β-ray detector. Dust concentration measuring means for determining the dust radioactivity concentration, nuclide analysis means for counting the output of the γ-ray detector to determine the interfering radioactivity concentration for the dust radioactivity concentration, and the dust determined by the dust concentration measurement means A dust radiation monitor comprising: a correction unit that corrects the radioactivity concentration by the interfering radioactivity concentration.