JP3822799B2 - Radioactive dust monitor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radioactive dust monitor, and more particularly to an apparatus for measuring dusty radioactive substances contained in a gas to be measured in a facility that handles radioactive substances.
[0002]
[Prior art]
Examples of facilities that handle RI (radioisotopes) include medical institutions, inspection institutions, nuclear power plants, and nuclear fuel processing engines. In such a facility, for the purpose of health (exposure) management of workers engaged in the facility, radioactive substances contained in gas (air) at each location (room, passage, workplace, etc.) within the facility It is necessary to measure the concentration. As a device for this purpose, a gas monitor and a dust monitor using a filter are conventionally known.
[0003]
The former gas-type gas monitor is a device that generally introduces gas into a measurement chamber and continuously detects radiation from a radioactive substance in a gas flow state. In general, the latter dust monitor is a device that detects a radiation from a radioactive substance contained in radioactive dust aggregated on the filter by allowing gas to pass through a filter such as filter paper having dust collecting properties. According to the latter radioactive dust monitor, there is an advantage that it can be measured in a state where the radioactive substance concentration is increased by collecting more radioactive dust on the filter. In addition, let the filter after dust collection stand for about two days, for example, natural radionuclides (detection interference nuclides) such as radon, thoron and their daughter nuclides with relatively short half-lives emitted from the wall of the facility. There is also a technique for reducing the concentration and measuring the radioactive materials (facility-specific nuclides) that are handled or generated at the facility with high sensitivity.
[0004]
[Problems to be solved by the invention]
By the way, in a facility handling RI, it is necessary to perform both external exposure management and internal exposure management for workers, as is well known. The external exposure management manages the exposure dose from the radiation source outside the body, and the internal exposure management manages the exposure dose from the radioactivity taken into the body by breathing or the like.
[0005]
Internal exposure control is to keep the exposure dose below the standard value stipulated by laws and regulations, and to monitor the amount of radioactive material floating in the air and notify the danger, thereby reducing the exposure dose and reducing the exposure dose. It is necessary to evaluate and confirm that it is below the reference value. In particular, when managing internal exposure of workers, there is a requirement for laws and regulations, and quantification of radioactive materials specific to facilities is required separately from natural exposure by radon, Tron and their daughter nuclides.
[0006]
In general, the above vented gas monitor is used for daily hazard notification, and internal exposure evaluation is carried out by calculating from the amount of RI used, measuring excrement, etc., and a dust monitor having a detection limit necessary for exposure evaluation. Has not been used because it is not suitable for daily hazard information.
[0007]
Therefore, in the past, separate methods or devices were required for danger notification and internal exposure evaluation. Incidentally, conventionally, for example, a method of actively switching the operating conditions of the apparatus according to a work schedule (operation schedule) of a facility for one week has not been adopted.
[0008]
This invention is made | formed in view of the said conventional subject, The objective is to provide the radioactive dust monitor which can measure a radioactive substance according to the work schedule of a plant | facility.
[0009]
Another object of the present invention is to provide a radioactive dust monitor capable of both internal exposure prevention and internal exposure evaluation by danger notification.
[0010]
Another object of the present invention is to immediately determine the increase in the concentration of dust-like radioactive material contained in the gas to be measured, and to accurately determine the concentration of the target radioactive material in a state where the concentration of the detection interference nuclide is reduced. It is to be able to measure.
[0011]
[Means for Solving the Problems]
(1) In order to achieve the above object, according to the present invention, in a radioactive dust monitor used in a facility that handles radioactive substances, a pump for sucking a gas to be measured, and the sucked gas to be measured pass, A dust collecting member that collects radioactive dust in the measurement gas, a measurement unit that measures radiation using a detector that detects radiation from the radioactive material contained in the collected radioactive dust, and the facility A schedule management unit that controls the operation of the pump and the measurement unit according to a work schedule that defines a work period and a work suspension period, and the schedule management unit sets the pump in an operating state during the work period, and the pump and stopped at the work pause time, the schedule management unit, release in storage by operating the measuring unit in the working period The first measurement was repeated a on sexual dust, characterized Rukoto to perform the second measurement against radioactive dust after storage by operating the measuring unit at a reduced state of the detection interfering species within the work pause.
[0012]
According to the above configuration, the operation of the pump is controlled by the control unit, that is, the operation / stop of the pump is switched according to the work schedule. Similarly, the operation of the measurement unit is controlled by the control unit.
[0013]
In a facility that handles radioactive substances, generally, the work time is defined for the entire facility, and similarly, the work suspension time is defined for the entire facility. Here, especially during the work, the external exposure management is indispensable. On the other hand, during the work suspension period, the external exposure management is not particularly necessary. Therefore, for example, the pump is stopped during the operation suspension period, and the concentration of the short-lived detection disturbing nuclides (mainly radon, thoron and their daughter nuclides) contained in the radioactive dust on the dust collecting member is reduced. If radioactivity is detected after the concentration is reduced, the target nuclide can be measured with higher sensitivity. That is, the detection limit can be lowered. Here, the target nuclide has a longer half-life than that of the detection-interfering nuclide.
[0014]
In addition, in the case where a work schedule is individually set for a work place, a work room, or the like, when the gas in such a place is to be measured, operation control may be performed according to such individual schedule.
[0015]
Nozomu Mashiku, the second measurement is set at the end of the work pause time.
[0016]
According to the above configuration, it is possible to perform continuous measurement or intermittent continuous measurement of radioactive substances during the work period, and reduce the concentration by using the short half-life of the detection interfering nuclides during the work pause period. In this state, the target nuclide can be detected with high accuracy. The execution timing of the second measurement is preferably set at the end of the work suspension period, but the execution time may be set automatically or may be determined by a user instruction. Moreover, you may make it switch a measurement calculation condition according to the presence or absence of replacement | exchange of a dust collecting member.
[0017]
Preferably, the first measurement is an abnormality monitoring measurement in a facility, and means for generating an alarm when the measurement result of the first measurement exceeds an abnormality determination value is provided. Desirably, the second measurement is a measurement for managing internal exposure of an operator by using nuclides other than radon, thoron and their daughter nuclides as the detection disturbing nuclides, and the second measurement is performed. , At least one of day, week and month. Preferably, the second measurement is performed on a daily and weekly basis, and the dust collecting member is replaced on a weekly basis.
[0018]
(2) In order to achieve the above object, the present invention relates to a portable radioactive dust monitor used in a facility that handles radioactive substances, and a pump that sucks a gas to be measured in the facility, and the suctioned object to be measured A filter unit holding the filter paper through which gas passes in an exchangeable manner, and a measurement unit that measures radiation using a detector that detects radiation from radioactive substances contained in the radioactive dust collected on the filter paper; A storage unit in which a work schedule that defines a work period and a work suspension period in the facility is registered; and a schedule management unit that controls operations of the pump and the measurement unit according to the work schedule; , first against radioactive dust in the accumulation by the measuring unit with the pump and the measuring unit in the operating state in the working period Characterized in that measurement to allow to allow the second measurement against radioactive dust after accumulation by the measuring unit by operating the measuring unit at a reduced state of the detection interfering nuclides the pump stopped at the work pause time And
[0019]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0020]
FIG. 1 shows a preferred embodiment of a radioactive dust monitor according to the present invention, and FIG. 1 is a conceptual diagram showing the overall configuration thereof.
[0021]
The radioactive dust monitor shown in FIG. 1 is configured as a portable device in the present embodiment. For example, in a RI handling facility or the like, the radioactive dust monitor is a device that measures the radioactivity concentration and the like of radioactive dust contained in indoor air. is there.
[0022]
In FIG. 1, a filter 14 for collecting radioactive dust is provided in the ventilation unit 10. The filter 14 is periodically replaced as needed or on a weekly or monthly basis.
[0023]
As shown in the drawing, an air flow path is formed in the ventilation unit 10 so that the taken-in gas is discharged through the filter 14.
[0024]
Incidentally, in the figure, reference numeral 12A indicates an air intake port, and reference numeral 12B indicates an air discharge port of the ventilation unit 10. A pump 12 is connected to the air discharge port 12B, and the pump 12 functions as an air suction source. The air sucked by the pump 12 is discharged from the air discharge port 18 to the outside.
[0025]
The detector 22 included in the measurement unit 20 is constituted by, for example, a radiation detector using a scintillator, and is arranged with its light receiving surface facing the filter 14. Specifically, the filter 14 is configured by, for example, filter paper, but the detector 22 is disposed facing the dust collecting surface side of the filter paper.
[0026]
In the measurement unit 20, the signal output from the detector 22 is input to the signal processing unit 24. The signal processing unit 24 includes an amplifier, a discriminator, a counter, and the like, and the count rate is calculated by the signal processing unit 24.
[0027]
As will be described later with reference to FIGS. 3 and 4, the calculation unit 26 is a circuit that calculates the concentration of radioactivity based on the input count rate, and the calculation result is output to the display unit 32. At the same time, the data is transmitted to an external computer or the like via the output unit 34. As will be described later, the calculation unit 26 has a function of detecting an abnormal state in which the concentration has rapidly increased. In such a case, an alarm is output.
[0028]
The control unit 28 manages the operation of the pump 12 and the measurement unit 20 according to the work schedule stored in the schedule memory 30. That is, the pump 12 is in an operating state during the facility work period, while the pump 12 is stopped during the facility work suspension period. And the measurement unit 20 performs the measurement mentioned later corresponding to such an operation | work period and an operation | work suspension period.
[0029]
The input unit 35 is configured by an operation panel or the like, and various commands can be input using the input unit 35, and a schedule can be registered.
[0030]
The battery 33 supplies power to each component in the apparatus. Incidentally, in the configuration shown in FIG. 1, the detected radiation is, for example, β-rays or γ-rays. Of course, other radiation may be detected. It is desirable to select the detector 22 as appropriate according to the type of radiation to be detected, and it is desirable to select the type of the detector 22 as appropriate according to the nuclide that is the measurement target.
[0031]
Further, in the present embodiment, the filter 14 constituted by filter paper or the like is manually replaced, but of course, the replacement can be automated. In this case, the replacement of the filter corresponds to the disposal of the used filter and the setting of a new filter.
[0032]
FIG. 2 shows the operation of the radioactive dust monitor shown in FIG. 1 in relation to the count rate graph. That is, in FIG. 2, the horizontal axis is the time axis, and the vertical axis indicates the measured count rate. In this example, a predetermined period is set as a work period within each day from Monday to Friday, and the rest of the night is a work suspension period. Q1 to Q6 in FIG. 2 indicate the above work period, and R1 to R5 in FIG. 2 indicate the above work suspension period. Here, the work suspension period indicated by R5 is a holiday on weekends and Sundays. Is included.
[0033]
In the present embodiment, filter replacement is performed manually, for example, prior to the start of Monday work periods Q1, Q6. In FIG. 2, the filter replacement period is indicated by S. After the filter replacement, the pump is in an operating state during each work period, and radioactive dust is gradually accumulated on the filter during the period. Therefore, as indicated by reference numeral 100, the counting rate shows a rising characteristic during the work period.
[0034]
On the other hand, during the work suspension period, the pump is stopped, and as a result, no new radioactive dust is collected. In the process, the concentration of the detected interfering nuclides with a short half-life gradually decreases. Therefore, the count rate characteristic as indicated by reference numeral 102 is obtained. In other words, it has a characteristic of a downward slump associated with the decay of the detection interfering nuclide.
[0035]
Here, paying attention to the work suspension period R5, the work suspension period R5 includes a two-day holiday, which further promotes the reduction of the concentration of the detected interfering nuclides.
[0036]
In the present embodiment, in each work period, the count rate is measured, for example, every minute, that is, the first measurement as the abnormality monitoring measurement is continuously performed in the work period. On the other hand, the continuous measurement as described above is not substantially performed during the work suspension period. However, as indicated by M9 in FIG. 2, the second measurement is performed for the internal exposure management of the operator prior to the filter replacement, that is, the measurement is performed in a single state in a state where the detected interfering nuclides are significantly reduced. To be implemented. Although the timing of the measurement may be specified in advance, the execution may be explicitly instructed by the user.
[0037]
As described above, in the work period, for example, count rates are acquired at 1-minute intervals, and a difference in count rates is calculated between temporally adjacent count rates. In Figure 2, for example, the difference value of the count rate M2, M3 are indicated by C _T.
[0038]
On the other hand, in the present embodiment, the second measurement (calculation) is performed for each day and for each week for the above internal exposure management. Specifically, the first measurement result in each work period is used. A difference value _CD is calculated between certain counting rates M1, M4, M5, M6, and M7, and based on the calculated value, the concentration of the radioactive material collected in each work period is calculated. In this case, since the pump is stopped during the work suspension period as described above, the concentration of the detection nuclide can be reduced by using the work suspension period, that is, the detection sensitivity of the target nuclide is increased. The concentration of radioactive material can be calculated in the state.
[0039]
By the way, even on Saturday, which is a holiday, measurement is carried out once, and the count rate indicated by the symbol M8 is thus obtained. From the comparison between M7 and M8, the amount of radioactive material accumulated in the work period Q5 on Friday is determined. Can be made.
[0040]
However, when calculating the concentration of the radioactive substance on a weekly basis described below, the calculation for each day is not necessarily required.
[0041]
In the present embodiment, the difference between the count rate M1 obtained by the measurement performed at the beginning of the week and the count rate M9 by the measurement performed prior to the filter replacement in the next week is calculated, and the difference value C _W Based on this, the radioactivity concentration over one week is calculated. That is, the concentration calculation as described above is performed in order to estimate the internal exposure amount of the worker in one week. Here, as described above, the work suspension period R5 includes holidays, and in particular, the concentration of detected interfering nuclides contained in radioactive materials collected on the previous Friday is significantly reduced. In the state, the count rate M9 is acquired. From the comparison between the count rate M9 and the count rate M1 corresponding to the background level, it is possible to estimate the amount of internal exposure within the work period of one week.
[0042]
3 and 4 are block diagrams showing the calculation process of the calculation unit 26 shown in FIG. Each function of the arithmetic unit 26 may be realized by an electronic circuit or may be realized by software processing. FIG. 3 shows a calculation method performed in the work period. The differentiator 40 receives the current count rate and the count rate before t time. Incidentally, the count rate before time t is, for example, stored in the memory 42. The t time is, for example, 1 minute. Differentiator 40 subtracts the time t before the count rate from the current count rate, thereby obtaining a difference value C _T.
[0043]
Divider 44 is a circuit for dividing the difference value C _T with integrated flow per time t. The result of the division is multiplied by a conversion factor K in a multiplier 46, whereby the radioactivity concentration is obtained. The determination unit 48 compares the radioactivity concentration with a determination value, and outputs an alarm when the radioactivity concentration exceeds the determination value or when the rate of change in radioactivity concentration exceeds the determination value. .
[0044]
FIG. 4 shows a configuration for realizing the concentration calculation for each day and the concentration calculation for each week. The difference rate 50 is input with the count rate in a state where the concentration of the detected interfering nuclides is reduced, and the initial count rate (initial value) of the day or week output from the memory 52 is input. In the difference unit 50, the difference values C _D and C _W are obtained by subtracting the first day or week count rate from the count rate in a state where the concentration of the detected interfering nuclides is reduced.
[0045]
The divider 54 executes a calculation for dividing the difference values C _D and C _W by the integrated flow rate over the entire measurement period. In the case of calculation for each day, this integrated flow rate corresponds to the integrated flow rate during the work period of the day, and in the case of calculation for each week, it corresponds to the integrated flow rate over the entire work period in that week.
[0046]
In the multiplier 56, the division result of the divider 54 is multiplied by the conversion coefficient K, thereby obtaining the radioactivity concentration. This radioactive concentration corresponds to the average concentration during the work period of each day, or corresponds to the average concentration within the work period of each week.
[0047]
Such a radioactivity concentration is output to the display unit 32 or the output unit 34, and the radioactivity concentration is converted into another physical quantity, for example, converted into a dose or the like, and the conversion result is obtained. Output / display.
[0048]
By the way, when the above difference calculation is performed, if the filter is not replaced at the beginning of the week, it goes back to the beginning of the week when the previous replacement was made and A difference operation is performed.
[0049]
FIG. 5 shows an example of the contents of the schedule memory 30 shown in FIG. As shown in the figure, a work start time and a work end time are designated for each day or each day of the week, that is, the period is defined as the work period. Then, the outside of the period is defined as the work suspension period. In addition, when performing the above-described measurement calculation for each week, it is necessary to perform a single measurement during the work suspension period, and the time condition in that case can also be specified. Of course, measurement may be manually instructed prior to filter replacement, without using such time designation.
[0050]
【The invention's effect】
As described above, according to the present invention, it is possible to rationally monitor radioactive dust according to the work schedule of the facility. Moreover, according to this invention, there exists an advantage that internal exposure prevention and internal exposure evaluation can be made compatible with a single dust monitor.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a radioactive dust monitor according to the present invention.
FIG. 2 is a diagram showing a relationship between a change in count rate and an operation of a radioactive dust monitor.
FIG. 3 is a diagram for explaining functions of a calculation unit shown in FIG. 1;
4 is a diagram for explaining a function of a calculation unit shown in FIG. 1; FIG.
FIG. 5 is a diagram showing the contents of a schedule memory shown in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Aeration unit, 12 Pump, 14 Filter (filter paper), 20 Measuring unit, 22 Detector, 24 Signal processing part, 26 Calculation part, 28 Control part, 30
Schedule memory.

Claims (6)

In radioactive dust monitors used in facilities that handle radioactive materials,
A pump for sucking the gas to be measured;
A dust collecting member through which the sucked measurement gas passes and collects radioactive dust in the measurement gas;
A measurement unit that measures radiation using a detector that detects radiation from a radioactive substance contained in the collected radioactive dust; and
According to a work schedule that defines a work period and a work suspension period in the facility, a schedule management unit that controls the operation of the pump and the measurement unit;
Including
The schedule management unit sets the pump in an operating state during the work period, stops the pump during the work pause period,
The schedule management unit operates the measurement unit in the work period to repeatedly perform the first measurement on the accumulated radioactive dust, and operates the measurement unit in a state where the detected interfering nuclides are reduced in the work suspension period. radioactive dust monitor, wherein Rukoto to perform the second measurement against radioactive dust after storage Te. The radioactive dust monitor according to claim 1,
The radioactive dust monitor characterized in that the second measurement is set at the end of the work suspension period. The radioactive dust monitor according to claim 1,
The first measurement is an abnormality monitoring measurement in the facility,
A radioactive dust monitor, comprising means for generating an alarm when a measurement result of the first measurement exceeds an abnormality determination value. The radioactive dust monitor according to claim 1,
The second measurement is a measurement for managing the internal exposure of the worker, with the nuclide other than radon, thoron and their daughter nuclides as the detection interference nuclides as measurement targets,
The radioactive dust monitor, wherein the second measurement is performed in units of at least one of a day, a week, and a month. In the radioactive dust monitor of Claim 4,
The second measurement is performed on a daily and weekly basis,
The radioactive dust monitor, wherein the dust collecting member is replaced on a weekly basis. In portable radioactive dust monitors used in facilities that handle radioactive materials,
A pump for sucking a gas to be measured in the facility;
A filter unit holding the filter paper through which the sucked gas to be measured passes in an exchangeable manner;
A measurement unit that measures radiation using a detector that detects radiation from a radioactive substance contained in the radioactive dust collected on the filter paper;
A storage unit in which a work schedule defining a work period and a work suspension period in the facility is registered;
A schedule management unit for controlling operations of the pump and the measurement unit according to the work schedule;
Including
The schedule management unit enables the pump and the measurement unit to be in an operating state during the work period to enable a first measurement of radioactive dust that is being accumulated by the measurement unit, and detects the pump in a stop state during the work pause period. A radioactive dust monitor, wherein the measurement unit is operated in a reduced state of interfering nuclides to enable second measurement of radioactive dust after accumulation by the measurement unit.

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