JPH06265638A - Dust radiation monitor - Google Patents

Abstract

PURPOSE:To exclude the missing of measurement immediately after the change of a flow paths by sampling the measured values of the flow rates during the transition period of a flowmeter at a short period over the specified time period immediately after the switching of the flow path of sampling gas into a sampling line. CONSTITUTION:A control device 2 imparts the opening command into a sampling valve 4 and imparts the closing command into a bypass valve 5. Thus, the flow path of the sampling gas from a pipe 1 is switched to a sampling line 2 from a bypass line 3. When the flow path is changed, the sampling gas is introduced into a collecting container 6. Dust is collected into filter paper 7 when the sampling gas passes the container 6. The radiation discharged from the radioactive nuclear species in the dust is counted in a detector 8. The counted value is sent into a data processing device 22. At this time, the measured values of the flow rates in the transition period of a flowmeter 10 are sampled in a short period over the specified time period immediately after the switching of the flow path. The concentration of the radioactivity is obtained in the processing device 22 based on the sampled average value of the flow rate and the detected signal value of the radiation.

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 collecting dust in the air and monitoring the radioactivity concentration in a nuclear facility or the like, and in particular, a flow rate fluctuation occurring in a transitional period when switching from a bypass line to a sampling line. Regarding the improvement of technology against.

[0002]

2. Description of the Related Art A general dust radiation monitor samples the air inside a facility building and introduces it into a collection container through a sampling line for continuous measurement, and also for sampling gas during background measurement or filter paper replacement. To the bypass line to temporarily bypass the collection container.

An example of the configuration of such a dust radiation monitor is shown in FIG.
Is shown in.

In this dust radiation monitor, sampling gas is drawn into the device through a sampling pipe 1. The sampling pipe 1 is branched into a sampling line 2 and a bypass line 3, and a sampling valve 4 and a bypass valve 5 are provided in each line.

A collection container 6 is provided in the middle of the sampling line 2. A filter paper 7 is arranged inside the collection container 6 so as to block the flow path of the sampling gas, and a radiation detector 8 is arranged opposite to the dust collecting surface of the filter paper 7.

The sampling line 2 and the bypass line 3 are branched once and then merged again and connected to the discharge system. An exhaust pump 9 and a flow meter 10 are provided in the pipe after the merging.

On the other hand, the switching operation of the valves 4 and 5, the measurement of the radiation amount of dust collected on the filter paper 7, the automatic feeding operation of the filter paper 7 and the like are controlled by the CPU 11 which forms the central function of the monitor main body.

The dust radiation monitor thus constructed operates as follows under the control of the CPU 11. First,
The CPU 11 gives a closing command to the sampling valve 4 of the sampling line 2 and an opening command to the bypass valve 5 of the bypass line 3, and in this state, the radiation detection signal output from the radiation detector 8 is measured for a certain period of time, Measure the ground.

Thereafter, the CPU 11 gives an opening command to the sampling valve 4 of the sampling line 2 and a closing command to the bypass valve 5 of the bypass line 3 to introduce the sampling gas into the collection container 6 and collect it on the filter paper 7. Measure the radiation dose of dust that is generated. At the same time, the flow rate measured by the flow meter 10 is taken in at regular time intervals, and the radioactivity concentration is calculated from the measured radiation dose and flow rate.

Immediately after switching the flow path of the sampling gas from the bypass line 3 to the sampling line 2, the flow rate of the sampling gas fluctuates greatly. This flow rate fluctuation occurs because the timings of the opening command and the closing command given to the valves 4 and 5 do not exactly coincide with each other, so that both valves open or both valves are closed.

When the flow rate fluctuates in this way, the error in the flow rate used by the CPU 11 to calculate the radioactivity concentration increases, so that after the switching of the on-off valve, the fluctuation in the flow rate becomes small and the measurement is started.

FIG. 6 shows the flow rate fluctuation state and the measurement timing when the on-off valve is switched. As shown in the figure,
Immediately after the flow path is switched to the sampling line 2,
Since the flow rate is unstable, the first measurement is performed after the elapse of a certain time Ta from the time of switching, that is, the flow rate measurement value is fetched from the flow meter 10, and the radioactivity concentration is calculated using the flow rate value. After that, the flow rate value is fetched from the flow meter 10 at a constant interval Tb to calculate the radioactivity concentration.

[0013]

As described above, in the conventional dust radiation monitor, in order to prevent the deterioration of the measurement accuracy due to the flow rate fluctuation immediately after the valve switching, the data is treated as missing during a certain period after the valve switching. Was not obtained.

The present invention has been made in view of the above circumstances, and reliability is improved by using a flow rate value with a small error even in the transitional period when the flow path of the sampling gas is switched from the bypass line to the sampling line. It is an object of the present invention to provide a dust radiation monitor capable of performing a high radioactivity concentration calculation and eliminating a missing measurement immediately after switching a flow path.

[0015]

In order to achieve the above object, a dust radiation monitor according to the present invention comprises a collection container having a dust collecting member, and a sampling gas introduced into the collection container and the collection container. A sampling line for guiding the gas that has passed through to the exhaust system, and a bypass line for guiding the sampling gas to the exhaust system by bypassing the collection container,
A radiation detector arranged to face the dust collecting member, a flow meter for measuring the flow rate of the sampling gas introduced into the collection container, and a flow path of the sampling gas between the sampling line and the bypass line. A line switching means for switching, and a transitional flow rate sampling for sampling the flow rate measurement value of the flow meter at a cycle shorter than the period at least immediately after the switching of the flow path of the sampling gas to the sampling line for a certain period immediately after the switching. Means, and a radioactivity concentration calculation means for obtaining a radioactivity concentration using the average value of the respective flow rate measurement values sampled by the transient period flow rate sampling means and the signal value of the radiation detection signal output from the radiation detector. Prepared and configured.

[0016]

In the dust radiation monitor of the present invention, when the flow path of the sampling gas is switched from the bypass line to the sampling line by the line switching means, the transitional period flow rate sampling means is shorter than the period at least immediately after switching for a certain period. The flow rate measurement value of the flow meter is sampled in a cycle. Then, each sampled flow rate measurement value and the radiation detection signal output from the radiation detector are input to the activity concentration calculating means, and the activity concentration is obtained from the average value of the flow rate measurement values and the signal value of the radiation detection signal. .

[0017]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 shows the structure of a dust radiation monitor according to an embodiment of the present invention. The parts having the same functions as those of the monitor shown in FIG.

The dust radiation monitor of this embodiment has a monitor main body 20 provided with a control device 21 and a data processing device 22.

The control device 21 has a first timer that determines the opening time of the bypass valve 5 corresponding to the background processing period and a second timer that determines the opening time of the sampling valve 4 corresponding to the radioactivity measurement period. And are built in, and the switching timing of the valves 4 and 5 is obtained based on the set time of the timer. The control device 21 is set to perform the replacement work of the filter paper 7 in conjunction with the switching operation of the valves 4 and 5. Further, a switching timing signal for the on-off valve is given from the control device 21 to the data processing device 22.

The data processing device 22 executes background processing, flow rate sampling processing, radiation detection signal input processing, and radioactivity concentration calculation processing according to the flow chart shown in FIG.

Next, the operation of this embodiment will be described with reference to FIG.

As an initial state, it is assumed that the sampling valve 4 of the sampling line 2 is closed and the bypass valve 5 of the bypass line 3 is open. In this state, since the sampling gas is guided to the discharge system through the bypass line 3, the sampling gas is not introduced into the collection container 6 and the dust of the sampling gas is not collected on the filter paper 7.

The control device 21 starts the first timer which sets the background processing period at the same time when the valves 4 and 5 are switched (S1). At the time when the timer reaches the set time limit, a switching timing signal is sent to the data processing device 22, and an opening command is given to the sampling valve 4 and a closing command is given to the bypass valve 5, so that the flow path of the sampling gas is bypassed. Switching from 3 to sampling line 2 (S2).

When the flow path of the sampling gas is switched to the sampling line 2, the sampling gas is introduced into the collection container 6. When the sampling gas passes through the collection container 6, dust in the sampling gas is collected by the filter paper 7. If the radionuclide is present in the dust collected on the filter paper 7, the radiation emitted from the nuclide is counted by the radiation detector 8, and the counted value is sent to the data processing device 22 as a radiation detection signal. Sent out.

Further, the control device 21 starts the second timer when the time limit for setting the first timer is reached. When the timer reaches the set time limit, a switching timing signal is sent to the data processing device, an open command is given to the bypass valve 5 and a close command is given to the sampling valve 4, and the flow path of the sampling gas is set to the sampling line 2. To bypass line 3. Along with that, filter paper 7
The paper feeding mechanism is controlled to replace the filter paper 7 (S3). Such operations of S1 to S3 are repeated.

On the other hand, the data processing device 22 is the control device 2
When the switching timing signal is given from 1, it is judged whether or not the bypass valve 5 is open (T1), and if it is open, the radiation detection signal of the radiation detector 8 is fetched to obtain the background (T2). In addition, during the period when the bypass valve 5 is open, since the replaced filter paper 7 before the dust collection is arranged by the above-described operation, the accurate background can be measured.

Next, when the switching timing signal is given to the data processing device 22 when the sampling line 2 is switched to the sampling line 2, the flow rate measurement value of the flow meter 10 is sampled at the sampling period Δt shown in FIG. Then, the radiation detection signal of the radiation detector 8 is taken in (T3) (T4).

Here, the sampling period Δt is set to a time sufficiently smaller than the period required for stabilizing the flow rate changed by the valve switching operation.

Then, the average value of the flow rate is obtained in units of 1 minute,
At the same time, the radioactive concentration is calculated from the total count rate counted during that period (T8). The average flow rate is the sampling period Δ
It is calculated by accumulating every t and dividing the accumulated flow rate after one minute by the number of sampling times. The integration start timing starts every minute immediately after the bypass line 3 is switched to the sampling line 2. In addition, the total count rate in one minute is obtained by sampling the radiation detection signal at every sampling period Δt.
The data processing device 22 uses the average flow rate and the total count rate every one minute to determine the radioactivity concentration C based on the following equation.

C = (Dλ / ηQ) · {N-BG (t2-
t1)} ÷ {(t2-t1)-(e- ^λt1- e
^-Λt2 ) / λ} where λ: decay constant (0.693 / nuclide half-life (min) D: deposition correction value Q: sampling flow rate (cm ³ / min) BG: background count rate (cpm) t1: counting start time t2: Counting end time η: Detection efficiency (cpm / Bq) N: Total count rate (count number) from t1 to t2 The data processing device 22 monitors the flow rate fluctuation during the sampling period from the flow rate measurement value (T5 ), When an abrupt change in the flow rate is detected, an alarm is output (T6), which makes it possible to know the case where the error is large even in the sampling with the sampling period Δt.

As described above, according to this embodiment, immediately after switching from the bypass line 3 to the sampling line 2, the flow rate is sampled at a sampling period Δt that is sufficiently shorter than the radioactivity concentration calculation period (1 minute interval). Since the radioactivity concentration calculation is performed using the average flow rate, the flow rate measurement error during the transition period from the bypass line 3 to the sampling line 2 can be suppressed to a small level, and the required radioactivity concentration error can be reduced. Moreover, it is possible to eliminate the missing period immediately after switching.

Although the monitor main body 20 is composed of separate hardware of the control device 21 and the data processing device 22 in the above embodiment, the control device 21 and the data processing device 22 are constituted by software 24 as shown in FIG. , 25 and 1
It can also be realized by one device.

Further, the sampling cycle Δ is set for one minute immediately after switching from the bypass line 3 to the sampling line 2.
The flow rate sampling by t may be performed, and thereafter, the flow rate may be measured at 1-minute intervals as in the conventional case. Except immediately after switching, the flow rate is stable, so accuracy does not decrease so much.

The present invention is not limited to the above embodiments, but various modifications can be made without departing from the gist of the present invention.

[0036]

As described above in detail, according to the present invention, highly reliable radiation using a flow rate value with a small error even in the transition period when the flow path of the sampling gas is switched from the bypass line to the sampling line. It is possible to provide a dust radiation monitor capable of performing active concentration calculation and eliminating missing data immediately after switching channels.

[Brief description of drawings]

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

FIG. 2 is an operation explanatory diagram of the embodiment shown in FIG.

FIG. 3 is a diagram showing a relationship between flow rate fluctuation and sampling time in the embodiment shown in FIG.

FIG. 4 is a diagram showing a modification of the embodiment shown in FIG.

FIG. 5 is a configuration diagram of a conventional dust radiation monitor.

FIG. 6 is an operation explanatory view of the dust radiation monitor shown in FIG.

[Explanation of symbols]

1 ... Sampling pipe, 2 ... Sampling line, 3 ...
Bypass line, 4 ... Sampling valve, 5 ... Bypass valve, 6 ... Collection container, 7 ... Filter paper, 8 ... Radiation detector, 9 ...
Discharge pump, 10 ... Flowmeter, 20 ... Monitor body, 21 ...
Control device, 22 ... Data processing device.

Claims (1)

[Claims] 1. A collection container provided with a dust collecting member, and a sampling line for introducing a sampling gas into the collection container and guiding a gas passing through the collection container to an exhaust system.
A bypass line that guides the sampling gas to the discharge system by bypassing the collection container, a radiation detector arranged to face the dust collecting member, and a flow rate of the sampling gas introduced into the collection container is measured. A flow meter, a line switching means for switching the flow path of the sampling gas between the sampling line and the bypass line, and when the flow path of the sampling gas is switched to the sampling line, for a certain period immediately after the switching. A transition period flow rate sampling means for sampling the flow rate measurement value of the flow meter in a cycle shorter than the period, an average value of the flow rate measurement values sampled by the transition period flow rate sampling means, and radiation detection output from the radiation detector. And a radioactivity concentration calculating means for determining the radioactivity concentration using the signal value of the signal The dust radiation monitor that characterized the door.