JPH04361190A - Radioactive dust monitor - Google Patents

Abstract

PURPOSE:To obtain the counting rate in a short time without under estimation in a radioactive dust monitor for measuring radiation by sampling radioactive dust. CONSTITUTION:Counting rate outputs measured with a counting rate meter 1 in every constant period are taken in a monitor part 2 and a storage part 3 as well. The monitor part 2 calculates the evolution of the counting rate output measured with the counting rate meter 1 in every constant period to take in a judgement part 4. The judgement part 4 compared and judges every time the evolution with a predetermined value regarded to have converged to 0. When the evolution value becomes lower than the judgement value, it output signal to cease the sampling to the sampler and an arithmetic part 5, cease sampling and start calculation in the arithmetic part 5. The arithmetic part 5 reads the counting rate output value of the counting rate meter at the time of cease of sampling which is in the storage part 3 and predicts the input counting rate from the counting rate meter 1 using a preset equation of time relation of the output, and outputs as the measured value.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method of measuring radioactive dust that uses a count rate meter to measure the radiation of radioactive dust floating in the air in the working environment and surrounding environment of a facility such as a nuclear power plant, as well as in the exhaust system of the facility. Regarding monitors.

0002

[Prior art] The conventional radioactive dust monitor was
As described in the prior art of Publication No. 5-134372, radioactive dust is collected from one sampling point to a filter in an airtight box in a dust sampler during a preset sampling time, and the dust increases over time. The counting rate of the radiation is measured using a radiation detector and a counting rate meter, and the counting rate at the end of sampling is converted into radioactivity concentration, and the same process as above is repeated by switching to the next sampling point to collect a large number of samples. Measuring points.

[0003] Also, the counting rate meter is JIS Z4316-1
For example, a first-order lag system is used, which has a predetermined time constant such that the statistical error is 10% or less as described in 978. The radioactivity concentration at the sampling point is determined by subtracting the natural counting rate from the counting rate at the end of sampling using Equation 1 and multiplying it by each coefficient.

0004

[Math 1]

[0005]

SUMMARY OF THE INVENTION The above-mentioned conventional technology uses the counting rate at the end of sampling to calculate the radioactivity concentration. Since the counting rate is an output value of a counting rate meter having a predetermined time constant, it does not follow the dust radiation that increases with sampling time and lags behind the input value. Furthermore, since measurement is performed by sequentially switching over a large number of sampling points with one radioactive dust monitor, missing measurements occur when focusing on one sampling point.

On the other hand, since the statistical error is determined by Equation 2, it is necessary to make the time constant of the counting rate meter long at a low counting rate in order to satisfy the above-mentioned JIS specifications.

[0007]

[Math 2]

[0008] From the above, the counting rate, especially at low counting rates with a long time constant, is underestimated because the relationship of measurement time≫time constant does not hold, and in order to avoid underestimation, the measurement time must be lengthened. There was a problem in that the missing time became long because

An object of the present invention is to provide a radioactive dust monitor that can measure the counting rate, which increases with collection time, in a short time and without underestimating it.

0010

[Means for Solving the Problems] The above-mentioned problem is solved by a monitoring means that sequentially obtains and monitors the time change by calculating the difference between the current value and the previous value of the output value of the count rate meter at fixed time intervals; determining means for determining that the time change in the output value of the count rate meter at fixed time intervals has converged to a constant value by comparing the output value of the monitoring means with a predetermined determination value; calculation means for predicting the count rate input value using a preset output time function calculation formula from the output value at each time; This problem can be solved by stopping sampling when it is determined that the amount of change has converged to a constant value, and outputting the count rate input value predicted by the calculation means as a measured value.

[0011]

[Operation] The above-mentioned monitoring means sequentially monitors the time change of the count rate output value of the count rate meter at fixed time intervals with respect to the dust radiation which increases with the collection time.

The determination means compares the output value of the monitoring means with a predetermined determination value, and determines whether the time change in the count rate output value of the count rate meter at fixed time intervals has converged to a constant value. This determines the shortest sampling time to predict the input value.

[0013] The calculation means predicts the input value of the count rate using a preset output time function calculation formula from the count rate output value of the count rate meter at fixed time intervals, and calculates the count rate input value of the count rate meter. By correcting the counting rate delayed by the time constant, it is possible to obtain it without underestimating it.

As described above, the counting rate can be determined in a short time and without being underestimated.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, while radioactive dust is collected by a dust sampler (not shown), radiation of the radioactive dust is detected by a radiation detector (not shown), and the detection signal is constant by a count rate meter 1 having a predetermined time constant. The count rate output value measured for each cycle is taken into the monitoring section 2 together with the sampling elapsed time, and at the same time is taken into the storage section 3. The monitoring unit 2 sequentially calculates the time change by calculating the difference between the current value and the previous value of the count rate output value measured at regular intervals by the count rate meter 1, and inputs it into the determination unit 4. The determination unit 4 determines whether the time change in the count rate output value measured by the count rate meter 1 at regular intervals is 0.
A successive comparison is made with a predetermined judgment value that can be considered to have converged to, and when the value is less than or equal to the judgment value, a sampling end signal is output to the dust sampler and the calculation unit 5, and the sampling is stopped.
The calculation section 5 performs calculations. The calculation unit 5 reads the count rate output value of the count rate meter at the time when sampling is completed from the storage unit 3, and predicts the input count rate of the count rate meter 1 from the preset output time function calculation formula. Output as a measured value.

Now, if the count rate meter is a first-order lag system with a fixed time constant T, the transfer function G(s) of the count rate meter is expressed by the equation 3.
Figure 2 shows a block diagram of the input and output of the counting rate meter.

[0018]

[Math 3]

The amount of radioactive dust collected is proportional to time since the suction flow rate is constant. In Figure 2,
Since the count rate input value Ri is proportional to the amount of dust, it is a lamp input that is proportional to time, and the count rate output value Ro of the count rate meter is expressed by the time function equation of Equation 4.

[0020]

[Math 4]

By setting Equation 4 in the arithmetic unit 5, the unknown constant K can be determined from the sampling end time and the counting rate output value Ro at that time, and the counting rate input value Ri can be obtained using Equation 5.

[0022]

[Math 5]

FIG. 3 shows the input/output time characteristics of this embodiment.

The characteristic 10a in FIG. 3 is the counting rate input value Ri, and the characteristic 10b is the counting rate output value Ro. Since the slope of Ro converges to a constant value over time, the comparator 3 successively compares the increment dRo of Ro at each fixed time dt with a predetermined determination value that indicates that the time change of dRo has converged to 0. The above Ro at time t when reaching the judgment value or less
is output to the calculation section 5. The calculation unit 5 calculates Ri from Ro and outputs it as a measured value.

In this embodiment, the case where the count rate meter 1 is a first-order lag system with a fixed time constant has been described. In the same way as above, the time change of the count rate output value of the count rate meter 1 at fixed time intervals is compared with a predetermined judgment value that can be considered to have converged, and the count rate output value of the count rate meter 1 is determined. By predicting the count rate input value from the output time function calculation formula set in advance in the calculation unit 5, the count rate can be determined in a short time and without being underestimated.

[0026]

[Effects of the Invention] According to the present invention, in a radioactive dust monitor that measures radioactive dust while sampling it using a count rate meter with a predetermined time constant, the count rate is determined in a short time and without being underestimated. be able to.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram illustrating a transfer function of one embodiment.

FIG. 3 is a time characteristic diagram of count rate input/output values in one embodiment.

[Explanation of symbols]

1... Count rate meter, 2... Monitoring section, 3... Storage section, 4... Judgment section,
5... Arithmetic unit, 6... Calculator.

Claims (1)

[Claims] Claim 1: In a radioactive dust monitor that consists of a dust sampler, a radiation detector, a count rate meter, and a calculator and measures radiation while collecting radioactive dust, the amount of time change in the output value of the count rate meter at regular intervals; a monitoring means for monitoring the above-mentioned time change, a determination means for determining whether the above-mentioned time change has converged to a constant value, and a counting rate using a preset output time function calculation formula from the output value at a certain time interval. A radioactive dust monitor comprising: calculation means for predicting input values.