JPS6134117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an iodine collection system for collecting iodine.

Prompt monitoring of the atmosphere inside the reactor containment vessel when a nuclear reactor accident occurs is extremely important, not only because it makes it possible to estimate the scale of the accident, but also because it provides powerful information for determining appropriate measures to deal with the accident. It is.

The most important fission products released upon fuel rod failure are highly volatile iodine,
and noble gases (Kr, Xe, etc.). These radioactive gas substances are important not only for estimating the extent of damage to fuel rods, but also for assessing radiation exposure to the human body.

Among the internal exposures received when inhaling released fission products, radiation from radioactive iodine is predominant.

However, sampling the air inside the reactor containment vessel during an accident has the following two major differences compared to normal sampling.

(1) Sampling air conditions are severe.

(2) The concentration of radioactive gas substances in the air is extremely high.

For this reason, it is required to collect iodine while overcoming various abnormal conditions at the time of an accident.

Iodine collection is carried out by adsorbing iodine onto a filter cartridge made of an iodine collection material. However, as described above, since iodine and rare gas exist in the sample air, the collection material ends up collecting these gases at the same time. Since the radioactive noble gas has a higher radioactive concentration than radioactive iodine, it is difficult to know the concentration of only the collected iodine.

The present invention has been made in view of these points, and an object of the present invention is to provide an iodine collection system capable of collecting only radioactive iodine by removing the radioactive rare gas after collecting it.

According to the invention, such an object is achieved by providing a pipe through which a sample gas containing iodine and a rare gas is safely guided, and a trap provided in this pipe and fitted with a filter cartridge made of an iodine collecting material. With the group,
A purge gas supply pipe branch-connected to the pipe in front of this collection section, and a first pipe installed in the pipe in front of this purge gas supply pipe and opened during the iodine collection period.
and a second valve provided in the purge gas supply pipe and closed during the iodine collection period, and after the iodine collection period ends, the first valve is closed and the second valve is opened to supply the purge gas. This is achieved by allowing the flow to flow through the collection section.

As a result of repeated experiments by the present inventors, it was found that rare gas has a weaker adsorption and adhesion force to the collection material than iodine, and therefore, the rare gas can be blown away with purge gas.

Therefore, in the present invention, a purge gas supply pipe is connected to the pipe at the front stage of the collection section in order to purge the rare gas collected in the filter cartridge. In addition to iodine, rare gases are also collected in the filter cartridge, but when radioactivity is measured in this state, the sum of the radioactivity of both radioactive gases (iodine and rare gases) is detected. Become. Therefore, the rare gas adsorbed on the filter cartridge, which has a relatively weak adsorption power, is removed by the purge gas.

Assuming a hypothetical accident at a nuclear power plant, in the worst case scenario, a large amount of water vapor will be present, and the pressure will reach a maximum of approximately 4 kg/cm ² G. Under these conditions, when activated carbon and silver zeolite are used as iodine trapping materials, various experiments have shown that a large amount of water vapor present in the sample air is adsorbed by the iodine trapping materials, resulting in a large amount of water vapor being collected. It was found that this decreases the iodine collection ability of the wood. Therefore, in other embodiments of the present invention, in order to maintain the iodine collection ability of the collection material at a high level over a long period of time, as described above,
The sample air is dehumidified. Furthermore, the sample air is heated to about 80°C in order to lower the relative humidity and reduce the adsorption of water vapor onto the collection material. As a result, more than 99% of iodine was recovered. Moreover, in addition to the above-mentioned iodine, a rare gas is also present in the sample gas. However, this rare gas is easily adsorbed to the collection material at low temperatures, but difficult to adsorb at high temperatures. By heating the sample air, it is possible to prevent the adsorption of rare gases onto the collection material, making it possible to collect only iodine.

Next, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a schematic diagram of an embodiment of the present invention. Sample air is guided into the pipe 1 from, for example, a reactor containment vessel. This pipe 1 has a valve 16
1, an iodine collection section 5, a valve 162, and a pump 7 are arranged in this order. The iodine collection section 4 is equipped with a filter cartridge 5 made of an iodine collection material such as activated carbon or silver zeolite. Further, a valve 163 is provided between the valve 161 and the collecting section 4.
A purge gas supply pipe 17 is connected thereto. Valve 161 is opened during the iodine collection period, while valve 163 is opened during the purge gas supply period.

Therefore, during the iodine collection period, the valve 161,
By opening valve 162, closing valve 163, and supplying sample air to piping 1, iodine in the sample air can be collected by filter cartridge 5. However, as mentioned above,
The rare gas also adheres to the cartridge 5 at the same time. Therefore, in order to remove this rare gas, after the iodine collection period ends, the valve 161 is closed and the valve 161 is closed.
3 is opened and a purge gas (eg, purge air or purge nitrogen) is supplied to the purge gas supply pipe 17. Thereby, the rare gas adhering to the collection material of the cartridge 5 can be blown away. Thereafter, all the valves 161, 162, 163 are closed, and the cartridge 5 is taken out from the collecting section 4.

FIG. 2 is a schematic diagram of another embodiment of the invention.
Sample air is likewise guided into the pipe 1 from within the reactor containment vessel. First, a dehumidifier 2 and a heater 3 are sequentially installed in this pipe 1. As the dehumidifier 2, for example, a water-cooled cooler, an air-cooled cooler, a semipermeable membrane dehumidifier, or an air dryer can be used. This dehumidifier 2 is
This is provided to remove moisture from the sample air containing a large amount of moisture so as not to reduce the ability of the collection section to collect iodine in the sample air. The sample air is cooled and its temperature is lowered in the pipe line guided from inside the reactor containment vessel into the pipe 1 or by passing through the dehumidifier 2. In that case, the relative humidity of the sample air increases, so in this example, the sample air is heated to about 80°C by the heater 3 in order to lower the relative humidity and maintain a high iodine trapping effect. .

A collection section 4 is provided in the pipe 1 downstream of the heater 3. In the collection section 4, iodine in the sample air is adsorbed onto the filter cartridge 5 and collected. The filter cartridge 5 is made of a collection material made of activated carbon, impregnated activated carbon, silver zeolite, etc., and is conveyed from the unused filter cartridge storage section 8 to the collection section 4 and set therein. When the sample air flows through the filter cartridge 5 in the collection section 4, iodine in the sample air is adsorbed to the collection material of the cartridge 5 and collected.

The sample air that has flowed through the collecting section 4 is sucked by the pump 7 via the flow rate measuring section 6, and is finally returned into the containment vessel.

On the other hand, in the filter cartridge 5, the radioactivity level of the adsorbed iodine is checked by the level monitor 9 in the collection unit 4.
monitored by. After the iodine collection is completed, the flow of sample air is stopped, and purge air or nitrogen or the like is supplied into the pipe 1 via the purge gas supply pipe 17 to flow through the filter cartridge 5. As a result, rare gases other than iodine adhering to the collection material of the filter cartridge 5 are blown away.

When the purge is completed, the cartridge 5 is automatically sent to the measuring section 21 and the radioactivity is measured. The measuring section 21 is equipped with a high level monitor 10 and a low level monitor 11, which are selectively used depending on the intensity of radioactivity in the cartridge 5, that is, the magnitude of the output of the level monitor 9.

Several tens of cartridges 5 are stored in the filter cartridge storage section 8, and the above-mentioned measurement operation is repeated until these cartridges are used up.

A measuring device 13 is connected to each level monitor 9, 10, 11, and these measuring devices 13
The output of is led to the arithmetic unit 14. Therefore, in this arithmetic unit 14, each level monitor 9, 1
The iodine concentration in the sample air is calculated based on the outputs of 0 and 11 and the output of the flow rate measuring section 6.

After each filter cartridge 5 has been measured, it is automatically transported from the measurement section 21 to the cartridge storage section 12 and discarded.

In addition, in Fig. 2, 161, 162, 16
Reference numerals 3, 164, and 165 indicate valves (electromagnetic valves) provided in the pipe 1, the purge gas supply pipe 17, and the sample air atmosphere discharge pipe 19, respectively; 18 indicates the valves provided in the pipe 1;
This is a pressure reducing valve installed in the The pressure of the sample air is reduced from high pressure (4 Kg/cm ² G) to approximately atmospheric pressure by this pressure reducing valve 18 . Further, 15 is a lead shield that covers each of the level monitors 9, 10, and 11, respectively.

3 to 9 show an example of an automatic radioactive gas collection and measurement device used in the system shown in FIG. 2.

First, refer to FIG. This FIG. 3 shows a plan view of the measuring device. This measuring device has a basic frame structure 120, which basic frame structure 1
On top of 20 are a collection section support frame structure 100, a measurement section support frame structure 110, a filter cartridge transport section support frame structure 130, and a filter cartridge storage section support frame structure 140.
and a filter cartridge slide mechanism support frame 150 are provided, respectively. The frame structure 100 includes a collection section 4, the frame structure 110 includes a measurement section 21, and the frame structure 130 includes a filter cartridge transport section 13.
0, the frame structure 140 has a filter cartridge storage section 8, and the frame structure 150
A filter cartridge slide mechanism 60 is supported by each of the filter cartridges.

As shown in detail in FIGS. 4 and 9, the filter cartridge storage section 8 is mainly composed of a storage tube 87 that stores the filter cartridge 5. As shown in FIGS. This storage tube is open at both ends.
Although the filter cartridge 5 can be stored through the upper opening, the cartridge is prevented from falling out through the lower opening. The storage section 8 also includes a motor 88, a shaft 89 that is moved up and down by the motor, and two limit switches 90 and 91. The shaft 89 is driven by the motor 88, enters the storage cylinder 87 from the lower opening, and uses its head 92 to push up the filter cartridge 5 stored in the storage cylinder 87. In this embodiment, 20 cartridges 5 can be stored in the storage cylinder 87. When the cartridge 5 is pushed out from the upper opening of the storage cylinder 87, this is detected by the limit switch 90 and the drive of the motor 88 is stopped. As a result, one cartridge 5 is placed in a state where it can be transported by a cartridge transport section 30, which will be described later. Note that 91 is for detecting the lower limit position of the shaft 89.

As shown in detail in FIGS. 5 and 7, the collecting section 4 mainly includes a cartridge receiving lower metal fitting 79.
and a cartridge receiving upper metal fitting 80. The lower metal fitting 79 has a through hole 79A, and an O-ring 84 is attached to surround the through hole 79A. Furthermore, a conduit 81 that constitutes a part of the piping 1 is connected to the through hole 79A. The lower metal fitting 79 is supported by a rectangular movable frame 76. This movable frame 76 has guide pieces 7 on both sides.
7 are fixed to each other, and this guide piece 77
Guide rods 78 respectively fixed to the support frame 83 pass through. In addition, the support frame 8
3 is fixed to the base frame structure 120. On the other hand, the bottom of the movable frame 76 is connected to the electric cylinder 7.
It is connected to the movable shaft of 5. This electric cylinder 75 is supported by the base frame structure 120 via a support frame 82. A spring 86 is inserted into the bottom of the movable frame 76. Furthermore, a moving rod 97 is coupled to the movable shaft of the electric cylinder 75, and movement of this moving rod 97 is detected by an upper limit switch 95 and a lower limit switch 96. On the other hand, the cartridge receiving upper metal fitting 80 is formed in the shape of a cylindrical container and similarly has a through hole 80A at the bottom. A rubber gasket 8 is attached to the upper metal fitting 80 so as to surround this through hole 80A.
5 is installed. A level monitor 9 is inserted into the upper metal fitting 80, and a lead shield 15 is attached to cover the level monitor 9. Upper metal fitting 80 and lead shield 1
5 is supported by a frame structure 100. Further, the pipe 1 is coupled to the metal fitting 80 through the lead shield 15. Note that the level monitor 9 consists of an ionization chamber.

Assume that the filter cartridge 5 is transported and placed on the lower metal fitting 79 by the filter cartridge transport section 30, which will be described later, as shown in FIG. Thereafter, by driving the electric cylinder 75, the movable frame 79 is moved upward using the guide rod 78 as a guide, and the lower metal fitting 79 is moved upward by the upper metal fitting 80.
be brought into close contact with Even after the close contact, the electric cylinder 75 pushes the movable frame 76 upward, but the pushing force is absorbed by the spring 86, and the collecting part 4 is prevented from being damaged by the pushing force. after that,
The upper limit switch 95 detects the upper limit of the movable axis of the electric cylinder 75 (that is, the upper limit of the moving rod 97). The electric cylinder 75 can be stopped. After that, the sample air is transferred from the pipe 1 to the through hole 80 between the upper metal fitting 80 and the level monitor 9.
A, the flow passes through the filter cartridge 5, the through hole 79A and the conduit 81 in sequence. At this time, iodine in the sample air is adsorbed and collected by the filter cartridge 5. In that case, the level monitor 9 monitors the radioactivity in the sample air flowing through the cartridge 5 and the piping. Thereafter, by sequence control, the movable shaft of the electric cylinder 75, that is, the lower metal fitting 79 is lowered downward, and when the lowering is detected by the limit switch 96, it is stopped and returned to its original state.

As shown in detail in FIGS. 3 and 8, the filter cartridge slide mechanism 60 mainly includes a movable plate 63 having a hole 68 and a movable plate 6.
3, a guide plate 64 having a hole 69 and on which the movable plate 63 is placed, and the shaft 6
2 and a motor 61 that drives the movable plate 63 on the guide plate 64. motor 61
is fixed to a support frame 70, and this frame 7
0 is fixed to the frame structure 150. The guide plate 64 passes through a measuring section 21 to be described later, and limit switches 65, 66, and 67 are attached to this.

When the filter cartridge 5 is brought from the collecting section 4 onto the slide mechanism 60 by the conveying section 30, the filter cartridge 5 is conveyed directly above the hole 68 in the state shown in FIG. 8A. after that,
Material band mechanism 36 (described later) of the conveyance section 30
When opened, the filter cartridge 5 is dropped into the hole 68 of the movable plate 63. Thereafter, by sequence control, the motor 61 is operated to move the shaft 62, that is, the movable plate 63 in the direction of arrow A, and the filter cartridge in the hole 68 is also carried in the direction of arrow A on the guide plate 64 at the same time. When the movable plate 63 reaches the limit switch 67, the operation of the motor 61 is stopped, and then the radioactivity of the filter cartridge 5 is measured in the measuring section 21. The filter cartridge is then brought to the center of the measuring section 21. In Figure 8,
B shows this measurement state. After the measurement is completed, the motor 61 is operated again and the movable plate 63 is moved in the direction of arrow B. The arrival of the movable plate 63 at a position where the hole 68 of the movable plate 63 and the hole 69 of the guide plate 64 coincide is detected by the cooperative action of the protrusion provided on the movable plate 63 and the limit switch 66, and the motor 61 is stopped again. In Figure 8, C
indicates this state. Since the hole 68 of the movable plate 63 and the hole 69 of the guide plate 64 coincide with each other, the filter cartridge falls into the cartridge storage section 12 through the hole 68. Thereafter, the operation of the motor 61 is restarted, the movable plate 63 is moved in the direction of arrow C, and when the protrusion provided on the movable plate is detected by the limit switch 65, the motor 61 is stopped and the movable plate 63 is returned to its original position. It returns to the state (the state shown in FIG. 8A).

As shown in detail in FIGS. 3 and 6, the filter cartridge conveying section 30 mainly includes a rotating arm plate 31, a material hand mechanism 36, a rotating shaft 44, and a Geneva mechanism for driving the rotating shaft (a prime mover 4).
7 and a driven wheel 48), a motor 50 that drives the prime mover 47, and a motor 34 that drives the material hand mechanism 36. The material hand mechanism 36 includes two arms 41 and 42 that intersect with each other, a fixed shaft 35 that rotatably supports these arms 41 and 42 and is fixed to the arm plate 31, and is coupled between the arms 41 and 42. A tension spring 39 is similarly arranged between arms 41 and 42 and is rotationally driven by a motor 34 via a shaft 37. It is composed of a rotating shaft rod 38. In addition, 33 is a bearing, 40, 45, 46, and 49 are limit switches, and 43 is a balance weight.

In the material hand mechanism 36, the two arms 41 and 42 are brought into a closed state by the action of a tension spring 39. The material hand mechanism 36 is brought to the filter cartridge storage section 8, collection section 4, or slide mechanism 60, and when it is necessary to open the material hand mechanism 36, the motor 34 is operated to rotate the rotary rod 38 and pull the arms 41, 42. It is opened against the force of the spring 39. When the arms 41 and 42 are opened, they abut against the limit switch 32, thereby causing the motor 3 to
4 is stopped. Therefore, the material hand mechanism 36 is connected to the filter cartridge storage section 8.
The filter cartridge 5 can be grasped in the collecting section 4.
can be released and grasped again, and further, the filter cartridge can be released in the slide mechanism 60. The rotating arm plate 31 is the third
In the figure, the slide mechanism 60 can be rotated approximately 180 degrees from the storage section 8. This turning drive is performed by rotating the turning shaft 44 by the motor 50 via a Geneva mechanism consisting of a driving wheel 47 and a driven wheel 48. The first position state of the transport section 30 is a state in which the material hand mechanism 36 is located in the storage section 8, and this is detected by the cooperative action of the balance weight 43 and the limit switch 45. Thereby, the motor 50 is stopped. Second
In the figure, when the conveyance section 30 is rotated clockwise by the operation of the motor 50 and the material hand mechanism 36 is brought to the collection section 4, this position is also changed between the balance weight 43 and a limit switch (not shown). Detected through cooperative action. Thereby, the motor 50 is stopped again. This positional state becomes the second positional state of the transport section 30. Next, when the motor 50 resumes operation, the conveyance section 30 is further rotated clockwise and the material hand mechanism 36 is brought onto the slide mechanism 60.
This position state is the balance weight 43 and limit switch 4.
It is detected by the cooperative action with 6. Thereby,
Motor 50 is stopped again. This position state becomes the third position state. In this way, the transport section 3
After gripping the filter cartridge 5 in the storage section 8, the filter cartridge 0 rotates 180 degrees clockwise and transports it to the collecting section 4 and the slide mechanism 60. And again
Rotate 180° to return.

As shown in detail in FIG. 4, the measurement unit 21 is arranged vertically facing the high level monitor 10 and the low level monitor 11, and the guide plate 64 of the slide mechanism 60 is placed between them. It is arranged. The high level monitor 10 consists of an ionization chamber,
Low level monitor 11 consists of a NaI scintillation detector. The filter cartridge 5 is carried between the monitors 10 and 11 by a slide mechanism 60 and measured.

Next, a series of operations of the automatic iodine collection and measurement device described above will be explained.

In this measuring device, various motors are controlled by sequence control based on the operation of limit switches.

In the state before starting measurement, the material hand mechanism 36 is brought into the storage section 8, and the arms 41 and 42 are opened. When the power is turned on in such a state, if the limit switch 90 does not transmit a detection signal for the filter cartridge 5, the motor 88 is operated to push the filter cartridge inside the storage tube 87 upward. As a result, when the filter cartridge comes into contact with the limit switch 90, the operation of the motor 88 is stopped. Thereafter, the motor 34 of the conveyance section 30 is operated to close the material hand mechanism 36, and the arms 41 and 42 are moved to the filter cartridge 5.
grab. When the limit switch 40 detects that the material hand mechanism 36 is closed, the motor 34 is stopped. After that, motor 50
is operated, and the material hand mechanism 36 is carried between the metal fittings 79 and 80 of the collecting section 4 while gripping the filter cartridge. The material hand mechanism 36 is then opened and the filter cartridge 5 is placed on the metal fitting 79 as shown in FIG. Then, by operating the electric cylinder 75, the fitting 79 is brought into close contact with the fitting 80, and then the sample air is forced to flow through the filter cartridge.
Iodine is collected. Next, purge gas is supplied to blow away the rare gas adhering to the filter cartridge. After that, the electric cylinder 75
By this operation, the metal fitting 79 is lowered. The material hand mechanism 36 grabs the filter cartridge after iodine collection, and the material hand mechanism 36 is brought onto the slide mechanism 60 by the operation of the motor 50, and the arms 41 and 42 are opened to move the cartridge onto the slide mechanism 60. Drop it into the hole 68 of the movable plate 63. Thereafter, the motor 61 of the slide mechanism 60 operates to move the movable plate 63 into the measuring section 21 and move the cartridge to the high level monitor 10.
and the low level monitor 11. After the measurement is completed, the operation of the motor 61 causes the
The cartridge is stored in the storage section 12 through the hole 69 of the guide plate 64. On the other hand, when the material hand mechanism 36 releases the cartridge, it turns 180 degrees in the direction of the arrow in FIG. 3 and returns to its original state (the position of the cartridge storage section 8). In this way, one measurement cycle ends.

As explained above, according to the present invention, by purging the rare gas from the filter cartridge that has adsorbed radioactive gas, only the iodine for collection purpose can be collected, and the piping system can also be purged. By doing so, it is possible to prevent dust from settling on the pipe wall. Furthermore, since the filter cartridge is removed after purging, there is an advantage that sampling air does not leak when removed.

According to this invention, not only rare gases but also other radioactive gases can be removed by purging.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG.
The figure is a schematic diagram of another embodiment of the present invention, Figures 3 to 5 show an example of a radioactive gas collection and measurement device used in the system of Figure 2, and Figure 3 is a schematic plan view thereof; FIG. 4 is a partially sectional front view of the same, FIG. 5 is a view taken along the line A-A in FIG. B is a schematic plan view thereof, B is a partially sectional front view thereof, FIG. 7 is an enlarged sectional view of the main part of the collection section in the radioactive gas collection and measurement device, and FIG. 8 is a filter car in the radioactive gas collection and measurement device. 9 is a schematic front view of the cartridge slide mechanism, A, B, and C are explanatory diagrams for explaining different operating states, and FIG. 9 is a schematic configuration diagram of the filter cartridge storage section in the radioactive gas collection measurement device. . 1...Sample air piping, 2...Dehumidifier, 3...
... Heater, 4 ... Collection section, 5 ... Filter cartridge, 6 ... Flow rate measuring section, 8 ... Filter cartridge storage section, 9 ... Level monitor, 10 ...
High level monitor, 11...Low level monitor, 12
... Filter cartridge storage section, 13 ... Measuring instrument, 14 ... Arithmetic unit, 15 ... Lead shield, 17
...Purge gas supply pipe, 18...Pressure reducing valve, 21...
...Radioactivity measurement department, 161, 162, 163, 16
4,165...Valve.

Claims (1)

[Claims] 1. A pipe through which a sample gas containing iodine and rare gases is guided, a collection section installed in this pipe and equipped with a filter cartridge made of an iodine collection material, and a pipe in front of this collection section. a purge gas supply pipe that is branch-connected to the purge gas supply pipe; a first valve that is provided in the pipe before the purge gas supply pipe and is opened during the iodine collection period; and a first valve that is provided in the purge gas supply pipe and is opened during the iodine collection period. and a second valve that is closed, and after the end of the iodine collection period, the first valve is closed and the second valve is opened to allow purge gas to flow through the collection section. .