JPS6057550B2 - Radioactive substance automatic monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-concentration radioactive iodine automatic monitoring device suitable for automatically measuring radioactive substances in a fluid.

Conventionally, in nuclear power plants, it is necessary to monitor the radioactivity concentration in the air or waste liquid in order to monitor the working environment and prevent radioactive materials from leaking outside the power plant.

This monitoring is performed constantly to prepare for unexpected situations, and for this reason it is desirable that the device be fully automated. In particular, radioactive iodine 131 has the characteristic of accumulating in the thyroid gland of the human body and has a long half-life of 8.05 days, so it is necessary to monitor extremely low concentrations of 10-10 μCi/Cc. Conventional devices for monitoring low-concentration radioactivity in gas pass sample gas through a collector filled with an adsorbent such as activated carbon to collect radioactivity, and then pass sodium iodide (N
Radiation is measured using radiation detection equipment such as a thallium (t1) (8l) detector.

In some cases, radioactivity is collected and measured at the same time. In this conventional method, an operator manually attaches the collector before use and removes it after use. However, when monitoring the radioactivity concentration at various locations such as in nuclear power plants, replacing them is a huge labor-intensive task. In addition, as another conventional method, there is a method in which a large number of collectors are arranged in advance in a storage container and used one after another by mechanical operation. However, even in this case, humans must insert the collector into the storage container and collect the used collector.
The frequency of this phenomenon has simply decreased compared to the conventional example described above. As described above, in the past, there was an inconvenience in that the collector had to be replaced and replenished by humans.

In addition, since it relies on human labor, there is a possibility of forgetting to replace or replenish the contents, and if you forget, you will not be able to carry out radioactivity monitoring that must be done constantly, which could lead to a serious accident. There is that too. Therefore, it is desirable to completely automate radioactivity monitoring devices and eliminate the need for human manual intervention. The purpose of the present invention is to automatically measure the radioactive concentration of radioactive substances without requiring any manual work by the operator! The purpose of the present invention is to provide an automatic monitoring device.

The present invention includes a plurality of cartridges filled with an adsorbent,
The cartridges are arranged in an endless manner at each of the mounting position, sampling position, measurement position and removal position, and each cartridge is circulated without changing the order. The device is installed so that it can be used, and configured to automatically continue collecting and measuring radioactive substances during cycles. That is, the cartridge can be used repeatedly, thereby eliminating the need for an operator to replace the cartridge. As a means of repeated use, we focused on the fact that the collected radioactivity naturally decays over time.
A large number of cartridges are arranged in an endless manner, and each cartridge is used at regular intervals without disrupting the order. Then, the elapsed time until the next use of the cartridge, which is given by the product of the usage cycle of each cartridge and the number of cartridges, is such that the radioactivity of the cartridge naturally decays to the extent that it does not affect the next reuse. In addition, a large number of cartridges are prepared or the usage cycle is determined. An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 1 to 3, reference numeral 5 denotes a rotary desk, which has a cartridge 11 attachment position 1, a sampling position 2, a measurement position 3, and a cartridge removal position 4. The cartridge 11 is a plastic cartridge outer cylinder 7.
An adsorbent 6 made of synthetic zeolite impregnated with silver is filled inside the adsorbent 6, and both ends are sealed with a wire mesh 9 whose mesh size is smaller than the particle size of the adsorbent 6. The mesh presser 8 fixes the wire mesh 9 to the cartridge outer cylinder 7, and at the same time fixes the wire mesh 9 and the cartridge 11.
By forming gaps on the upper and lower surfaces of the cartridge 1
This serves to prevent the wire mesh 9 from being worn out due to contact with other structures during movement. Further, a cartridge protrusion 10 is fixed to the cartridge outer cylinder 7 at right angles to the axial direction of the outer periphery at the center or slightly above it. As the rotary disk 5 rotates, the cartridge 11 is placed on the rotary disk 5 at the cartridge mounting position 1, and the sampling section 2
The radioactive iodine in the sample gas is collected at the measurement position 3, and after the collected radioactivity is measured at the measurement position 3, the rotary desk 5 is removed at the removal position 4.
removed from. The rotary desk 5 is made of stainless steel and is hollow to reduce weight, and has storage holes for storing cartridges 11 at intervals of 900 mm on the same circumference concentric with the rotating shaft (not shown) on the plate surface. 11A is provided.

The storage hole 11A is provided with a small diameter part at the lower part, and the cartridge protrusion 10 of the cartridge 11 is placed in this small diameter part, so that the upper end of the cartridge 11 is approximately 1 TKI above the upper surface of the rotary disk 5.
R is becoming more prominent. The rotating desk 5 rotates counterclockwise by 90 degrees every 12 hours, and at its stop position rotates by 4 degrees.
Corresponding to the storage holes 11A, the cartridge 11 is installed in the following order: mounting position 1, sampling position 2, measurement position 3.
, there is a cartridge removal position 4. At the top of the mounting position 1, there is a storage container 1 that stores the cartridge 11.
2, and as the rotary disk 5 rotates, the cartridge 11 falls from the storage container 12 into the storage hole 11A of the rotary disk 5 and is supplied to the disk 5.

At the top of the sampling position 2 is a sampling section top lid 13.
is fixed separately from the rotary desk 5. In addition, a sampling lower lid 14 that is movable up and down is provided at the bottom,
When the rotary desk 5 rotates, the sampling lower lid 14 is lowered to the lowest end so as not to interfere with the rotation.
While the rotary disk 5 is stopped, the cartridge 11 is pressed onto the sampling top lid 13 by a hydraulic device or the like. During this pressure bonding, an O-ring 16 is installed between the protrusion 10 of the cartridge 11 and the sampling upper lid 13 and sampling lower lid 14, respectively, to prevent the sample gas introduced from the sampling section inlet pipe 17 from leaking. At this time, the lower lid guide 15 fixes the position of the sampling lower lid 14. The bellows arrangement 19 connects the sampling section outlet pipe 18 and the fixed pipe 38 and allows the sampling lower cover 14 to move up and down. The sample gas is sucked in by a proer (not shown), etc., and then passed through the sampling section inlet pipe 1.
7, passes through the cartridge 11, is adsorbed by the iodine cartridge 11 in the sample gas, and then exits from the sampling section outlet pipe 18.

Further, the sampling section outlet pipe 18 is provided with a valve (not shown), and this valve is opened only while the sampling lower cover 14 and the cartridge 11 are being crimped. The cartridge 11 that has finished collecting iodine moves to the measurement position 3, where the collected radioactivity is measured by a detector 22 consisting of a NaI (t) detector.The signal passes through the signal line 23 and is counted. The upper shield 20 and the lower shield 21 are made of thick lead walls, and are spaced from the rotary desk 5 by approximately 2Tfr!n. The completed cartridge 11 is moved from the measurement position 3 to the removal position 4 by the rotation of the rotary disk 5.

Here, the cartridge 11 is pushed upward by the pusher 24, taken out from the storage 11A, and stored in the storage container 2. Four stoppers 27 are attached to the lower end of the storage container 26 at intervals of 90 mm each.
Although it is movable inside the storage container 26, it is not movable outside, and does not prevent the cartridge 11 from being inserted, and prevents it from falling to the outside. Storage container 2
The cartridges 11 are stacked in the cartridge 6 in the order in which they are inserted, and the cartridge 11 located at the top is lifted up each time a cartridge 11 is inserted from the bottom. When it reaches the highest position, the upper rotary plate 28 rotates 90 degrees counterclockwise, and at the same time, the feed claw 29 moves the uppermost cartridge 11 from the storage container 26 to the delivery path 39 that connects the storage container 12. send to. The delivery path 39 is inclined, and rollers or the like are attached to the floor surface thereof, so that the cartridge 11 slides toward the storage container 12 and is located at its uppermost end.

On the other hand, the pusher 24, which had been stopped during the rotation of the upper rotary plate 28, descends after its rotation and returns to the lower position of the rotary disk 5. The pusher guide 25 is the pusher 24
It is provided to smoothly move up and down. In this way, as the rotary disk 5 rotates by 900 degrees, the cartridges 11 do not become out of order with respect to each other. The storage containers 12 and 26 are large enough to accommodate a row of cartridges 11 stacked vertically as shown in FIG. The cartridges 11 sequentially move downward within the storage container 12' and sequentially upward within the storage container 26. In addition, in this embodiment, the cartridge 1
As the adsorbent 6 used in Example 1, an adsorbent in which silver was supported on synthetic zeolite was used.

This adsorbent is made of activated carbon, which was conventionally used to adsorb iodine etc. in gases, or potassium iodide (KI) added to activated carbon.
Compared to carbon impregnated with organic amines such as tin iodide (SnI2), and triethylenediamine (TEDA), it is more effective at adsorbing moisture in the atmosphere and impurity gas such as nitrogen dioxide (NO2). The decrease in iodine collection efficiency due to this is extremely small. This has been experimentally confirmed by the present inventors, and is also clear from known literature. Therefore, the decrease in efficiency due to contact of the cartridge 11 with the atmosphere during storage can be ignored, and as a result, the storage containers 12, 26 and the delivery path 39 are not sealed against the atmosphere, and the filling of the cartridge 11 is eliminated. , the collection mechanism has been greatly simplified. It has been experimentally confirmed that similar effects can be obtained with an adsorbent in which silver or a compound containing silver is supported on a carrier mainly composed of silicic acid and alumina, and it is also clear from known literature. The aeration flow rate of the sample gas was 60 liters per minute during the experiment conducted by the present inventors, and since the rotation desk 5 was rotated every full hour, the sampling amount was about 40 d.

Moreover, the iodine collection efficiency of this cartridge 11 is 95
% or more can be secured in the container, and the concentration of iodine 1311 is 10
If it is -11 μCi/Cc or more, the radioactivity collected by the cartridge 11 will be approximately 0-4 μCi or more. Detector 22
The detection efficiency of 3% or more can be easily ensured, and the calculated value of iodine-1311 is about 15,000 counts or more after 1 hour of measurement. Upper and lower lead shields 20 with a thickness of 5C771,
By enclosing the detector 22 with 21, it is easy to reduce the natural counting rate of the detector 22 to 2 PCS (count percent) or less even when there are several gaps between the lower shield 21 and the rotary desk 5. Therefore, it can be easily identified from the total natural count value of 90,000 cant during the measurement time of one full hour. In addition, actual measurements have shown that the fluctuation range of iodine radioactivity concentration at nuclear power plants, etc. is about two digits at most, so the usage range of the monitoring device should be set at 10-8 to 10 Assume -11 μCi/Cc.

In this case, the force that collected the maximum concentration of 10-8 μCi/Cc.
Using the chamber 11, the lowest concentration of 10-11 μCi/
In order to measure Cc, it is sufficient if the strength decreases by four orders of magnitude or more upon reuse. As a result, the period until reuse is 110 days, and the number of cartridges 11 to be used is 22 days. ．． According to experiments, the iodine adsorption capacity of the cartridge 11 is approximately 18% by weight of iodine.
f or more, and the iodine concentration in normal air is at most 10-
Since it is 5f1/i, the number of times it can be used is 400.
0 old or older. 4 to 10 show other embodiments. The difference from the above embodiments is that radioactive iodine in the sample gas is collected into the cartridge 11 and measured at the same time. Therefore, the detector 22 is attached to the sampling position 2, and the number of cartridge accommodating holes 11A in the rotary disk 5 is three. The rotary disk 5 rotates by 120 volumes, and with the rotation, the cartridge 11 is moved to the mounting position 1.
, sampling position 2, measurement position 3, and removal position in this order. The mechanisms at the attachment position 1 and the removal position are the same as in the above embodiment. Movement and replacement of the cartridge 11 is controlled by a controller 32 consisting of a small computer.

The rotary disk driving machine 34 is driven by a signal from the controller 32, and sends a completion signal to the controller 32 when the rotary disk 5 has rotated 1202 times. Upon receiving this signal, the controller 32 sends a signal to the sampling lower lid driver 35 to raise the sampling lower lid 14. As a result, the cartridge 11 that has been moved to the sampling position 2 and the measurement position 3 is pressed onto the upper shield 20 via the O-ring 16. The controller 32 receives the signal that the crimping has been completed from the sampling lower lid driver 35, opens the solenoid valve 33 attached to the fixed pipe 38 between the blower and the bellows pipe 19, and simultaneously
A signal to start counting is sent to the counter 31. Accordingly, the sample gas is introduced from the sampling section inlet pipe 17, passes through the cartridge 11, the sampling section outlet pipe 18, the bellows pipe 19, the fixed pipe 38, and the electromagnetic valve 33, and is sucked into the blower. The controller 32 sends a counting end signal to the counter 31 when the count value of the counter 31 reaches a preset value, or when one hour of rotation period of the rotary desk 5 has passed, and at the same time sends an electromagnetic signal to the counter 31. Venting of the sample gas is ended by closing the valve 33.

36 is a pusher driver, and 37 is a display.

After the above-mentioned counting and ventilation are completed, the sampling lower lid drive 35 is driven to lower the sampling lower lid 14, and then the rotary desk 5 is rotated to replace the cartridge 11.
However, in order to keep the measurement cycle constant, the elapsed time from the start to the end of ventilation is set to a rotation period of 12fI! If it is shorter than f, the above operation is performed when 12BI of the rotation period has elapsed. In Figure 6, the rotation period of the rotary desk 5 is TO, and the radioactive concentration of iodine (131■) at normal times is Q.
.

shall be. The half-life of 1311 is 8.05 days, so TO
When the time is about 12 hours, the natural attenuation of the collected radioactivity is ignored, and the collected radioactivity at this time increases in proportion to the sampling time.

Assume that the radioactivity concentration in the sample gas increases to Q1 at a certain time. In FIG. 7, the radioactivity collected in the cartridge 11 at this time is shown by a curve A shown by a dashed line.
Curve B shown as a solid line is the normal concentration Q. This is the collected radioactivity curve at the time of . As the radioactivity collected in the cartridge 11 increases, the count value of the counter 31 increases as shown in FIG. In FIG. 8, the solid line curve B shows the case where the concentration is normal, and the dashed-dotted line curve A shows the case where the radioactivity concentration increases to Q1 in FIG. 6 at the sampling time. In FIGS. 7 and 8, curve C shows a case where the radioactivity concentration is higher than curve A. In FIG. 5, the count value on the display 37 is a predetermined value C.

When this happens, sampling ends. Therefore, sampling is stopped at the time of the seventh group 1, and the radioactivity collected by the cartridge 11 at this time is a smaller amount of radioactivity P1 than when it was at the sampling position at the TO time. FIG. 9 shows the ratio P1/PO of the amount of collected radioactivity to Q1/QO, which indicates an increase in concentration, using t1/TO as a parameter. Count value C. Accumulated radioactivity amount P1 when reached
The case where sampling is controlled to be stopped at
= 0.67) Two-dot chain curve c (t1/TO = 0.9
), and the solid line curve B (t1/TO=o) shows the case where t casting interval sampling is performed. From Figure 9,
For example, it can be seen that even if the concentration of 1311 in the sample gas suddenly increases to 10 f8, the collected radioactivity is only 10 f8. Normally, in a nuclear power plant, the concentration change of 1311 is about 10 CPi at most;
Consider the case where the concentration is 0 times higher.

Even in this case, the collected radioactivity is at most 3C@, and the 10th
As shown in the figure, the number of days required for next reuse is 67 days, which is approximately 213 days compared to 107 days when 100 radioactivity samples are collected by time sampling. As a result, when the rotation period of the rotary desk 5 is one full, the number of cartridges 11 to be prepared can be reduced to approximately 213 to 14 by stopping sampling when the count value CO is reached, and the number of cartridges 11 to be prepared can be reduced to approximately 213 to 14 cartridges. Light weight and miniaturization can be achieved. Also, when the radioactivity concentration in the atmosphere increases rapidly, the sampling time T. Such an abnormality warning can be issued early at time t1 without elapsed. These are the effects of this embodiment. In the case of this embodiment, a case has been described in which a small computer is used as the controller 32, but the count value of the counter 31 is converted into voltage, and when a predetermined voltage is reached, a differential pressure oscillator or the like is used to convert the sample gas It is also possible to control by issuing a signal to end ventilation and measurement.

Further, in this case, the cartridge exchanger such as the rotary desk 5 and the crimping of the sampling position can be performed by mechanical operation or by electric signals from a timer or the like. This embodiment is as described above, and has the effect of being able to automatically and precisely measure the low concentration of gaseous iodine radioactivity in a nuclear reactor plant completely unattended.

Furthermore, since the cartridge for collecting radioactive iodine is repeatedly reused, it also has the effect of not generating radioactive waste. According to the present invention, the first
A large number of cartridge filters can be easily moved in sequence within the closed loop connecting the storage container, rotary desk, second storage container, filter transfer path, and first storage container, so radioactivity of the sample gas can be continuously measured unattended. Can be measured accurately.

Furthermore, since the cartridge filter is reused, the generation of radioactive waste can be significantly suppressed.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, and is a schematic diagram of a rotary desk of the low-concentration radioactive iodine automatic monitoring device of the present invention;
Figure 2 is a longitudinal cross-sectional view of the cartridge attached to the rotary disk in Figure 1, Figure 3 is a detailed cross-sectional development view of the cartridge storage hole in the rotary disk in Figure 1, and Figure 4 is the low-concentration radioactive iodine of the present invention. FIG. 5 is a block diagram of the control unit of the device shown in FIG. 3; FIG. 6 is an explanatory diagram of radioactivity concentration and sampling time; Figure 7 is an explanatory diagram of the accumulated radioactivity amount and sampling time of the device in Figure 4, Figure 8 is an explanatory diagram of the measured count number and sampling time of the equipment in Figure 4, and Figure 9 is an illustration of radioactivity concentration increase. Collected radioactivity amount ratio P1/ to ratio Q1/9
An explanatory diagram showing PO using the sampling time ratio t1/TO as a parameter, and FIG. 10 is an explanatory diagram of the adsorption radioactivity multiple and the number of days elapsed. Explanation of symbols 1...Mounting position, 2...Sampling position, 3...Measuring position, 4...
...Removal position, 6...Adsorption material, 11...
··cartridge.

Claims (1)

[Claims] 1. A rotating disk having a plurality of storage holes in the circumferential direction for storing cartridge filters filled with adsorbent, and a first storage container storing therein a large number of the cartridge filters to be supplied to the storage holes of the rotating disk. a means for supplying a sample gas to the cartridge filter installed in the storage hole of the rotary disk; a means for detecting radioactivity of the cartridge filter to which the sample gas is supplied; and a portion below the rotary disk. a means for pushing up the cartridge filter installed in the storage hole of the rotary desk; and a means opposite to the pushing-up means;
a second storage container disposed above the rotary disk and housing the cartridge filter removed by the push-up means into the interior from the lower end, and the cartridge filter on the rotary disk is is movable from the first storage container to the second storage container via the sample gas supply means and the radioactivity detection means,
A radioactive substance automatic monitoring device in which the first and second storage containers, the sample gas supply means, and the radioactivity detection means are sequentially arranged in the rotational direction of the rotary desk,
The first and second storage containers have a size that accommodates a large number of the cartridge filters in a line in the vertical direction,
A filter transfer passage for sequentially transferring the cartridge filter from the second storage container to the first storage container is attached to the upper end portions of the first and second storage containers, and is located at the top in the second storage container. means for feeding the cartridge filter into the filter transfer passage;
An automatic radioactive substance monitoring device characterized by being installed at the upper end of a storage container.