JPS6364760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cleaning device for a fuel assembly of a boiling water nuclear reactor or the like. In general, a fuel assembly for a boiling water nuclear reactor is constructed by housing a fuel handle in which fuel rods are arranged in, for example, 8 rows and 8 columns, and assembled into a channel box. The coolant then flows upward between the fuel rods, moderating the neutrons and removing the generated heat. By the way, this coolant contains corrosion products (crud) generated from reactor internal structures, piping, etc., and this crud adheres to the surfaces of the fuel rods. Therefore, crud accumulates on the surface of the fuel rod over time, causing problems such as deterioration of heat transfer coefficient. Additionally, when transporting spent fuel assemblies to a reprocessing plant or when reprocessing them after transport, there is a problem in that the radiation dose to workers increases due to the high radiation emitted from the crud attached to the fuel rods. . For this reason, the crud adhering to the fuel rods has conventionally been periodically removed, and this method will be explained with reference to FIG. 1. Figure 1 briefly shows the fuel handling equipment and surrounding structures located in the upper part of the reactor core. 1 is the reactor core,
2 is a reactor pressure vessel, and 3 is a reactor containment vessel. A fuel pool 5 and an equipment storage pit 6 are provided on both sides of the reactor well 4 provided in the upper part of the reactor pressure vessel 2, and during operation, the reactor well 4 is accessed through a gate 7. The influx is blocked. Inside the fuel pool 5, a rack 9 for fixing a fuel assembly 8 is provided on the bottom wall 22 of the fuel pool 5. Note that 23 is a side wall of the fuel pool 5. During periodic inspections, a fuel exchange platform 12 equipped with a hoist mechanism 11 combined with a fuel gripper 10 is moved between the top of the reactor core 1 and the fuel pool 5 on rails (not shown) on the operation floor of the reactor building. The spent fuel assembly 8 is removed from the reactor core 1 and transferred into the fuel pool 5. In this fuel pool 5, crud adhering to the fuel rods is removed. To remove this crud, first the channel box is removed from the fuel assembly 8. In this state, the fuel assembly 8 was cleaned by spraying a jet of high-pressure water, or a worker removed crud from the fuel assembly 8 with a brush or the like. However, with this method, workers are exposed to a large radiation dose during work, it is troublesome to recover the removed crud, the entire fuel pool 5 is contaminated with radioactivity, and the cleaning effect is not necessarily sufficient. There was a problem. The present invention has been made in view of the above points, and its purpose is to easily and completely remove and collect crud adhering to the surface of fuel rods, reduce the radiation dose of workers during work, and An object of the present invention is to provide a cleaning device for a fuel assembly in which the entire fuel pool is not contaminated by radiation. An embodiment of the present invention will be described below with reference to FIGS. 2 to 4. FIG. 2 shows a schematic configuration of the present invention, and FIGS. 3 and 4 show it in more detail. In the figure, reference numeral 15 denotes a container body, and this container body 15 has a cover 14 that can be opened and closed at its upper part, and is installed in the fuel pool 5. There is a gap between the top of the lid 14 and the water surface of the fuel pool 5 that is longer than the length of the fuel assembly 8, and a space that allows the fuel assembly 8 to be moved underwater without being exposed from the water surface. is ensured. Further, the lower part of the container body 15 has a conical shape and is structured so that no water remains in the container body 15 when the water inside the container body 15 is drained. A fuel assembly drive device 16 is provided in this container body 15. Reference numerals 16f and 16g are supporting metal fittings, and these supporting metal fittings 16f and 16g support the fuel assembly 8 so as to be rotatable and vertically movable. And these support fittings 16f,
16g is attached to a belt 16e stretched between pulleys 16c and 16d. This belt 16e is connected to the motor 1 via a coupling ring 16b.
6a, and the fuel assembly 8 is moved up and down together with the support fittings.
Further, the fuel assembly 8 is configured to be rotated by a rotation mechanism (not shown). A pressurized gas supply mechanism 17 for draining the pool water in the container body 15 is provided. Reference numeral 17a denotes a compressor, which supplies high-pressure gas, such as pressurized air, into the container body 15 via an on-off valve 17b and a pressure air supply pipe 17c, and discharges water from the container body 15. It is structured as follows. Next, a cleaning mechanism 18 for cleaning the fuel assembly 8 is provided. 1
8a is a high-pressure jet pump, and this high-pressure jet pump 18a is driven to supply water to the water tank 18b.
The cleaning water inside is sprayed onto the fuel assembly 8 from a nozzle 18d via a cleaning water supply pipe 18c. Further, the nozzle 18d is installed in the container body 15 so as to surround the fuel assembly 8, as shown in FIG. Next, the cleaning liquid purification and discharge mechanism 19 is connected to the lowest part of the container body 15 and includes a discharge pipe 19b having an on-off valve 19a, a drain pump 19c, a filter 19d, etc., all of which are installed in the fuel pool 5.
After the fuel assembly 8 is cleaned by the fuel assembly cleaning mechanism 18 , the drain pump 19c is driven to discharge the cleaning water and crud accumulated in the container body 15 through the on-off valve 19a and the discharge pipe 19b. The crud is removed and collected by the filter 19d, and the clean washing water is sent to the fuel pool 5.
The structure is such that it returns to the inside. Next, the gas purification exhaust mechanism 20 includes an air filter 20a and an exhaust pipe 20c that branches from the pressure gas supply pipe 17c of the pressure gas supply mechanism 17 and has an on-off valve 20b, and carries the air exhausted from the container body 15 to the exhaust pipe 20c. , the air is sent to an air filter 20a via an on-off valve 20b and is purified. Note that the air in the container body 15 is exhausted by supplying water into the container body 15 by a water supply mechanism 21 , which will be described below. The water supply mechanism 21 is a water supply pump 21 installed on the floor outside the fuel pool.
a and an on-off valve 21b, this water supply pump 2
The water sent by 1a is configured to be supplied into the container body 15 via a water supply pipe 21c connected to the container body 15. In addition, the reference numeral 21d in FIG. 3 is a suction pipe connected to the water supply pump 21a. The operation will now be explained based on the above configuration. First, in FIG. 2, the gates 7 are sequentially removed and the reactor well 4 is filled with water. Then, the fuel assembly 8 is lifted from inside the reactor core 1 by the fuel gripper 10 of the fuel platform 12 and moved into the fuel pool 5. Therefore, the channel box (not shown) is removed from the fuel assembly 8 underwater. Then, the lid body 14 is removed and the fuel assembly 8 with the channel box removed is placed in the container body 15.
Store inside. And the support fitting 1 of the drive device 16
The fuel assembly 8 is fixed with 6f and 16g. Therefore, the lid 14 is placed over the container body 15 and fixed tightly. Next, the compressor 17a of the pressurized gas supply mechanism 17 is driven to supply pressurized air, and the opening/closing valve 17b is opened to supply pressurized air at the container body 15. At the same time as the above operation, the on-off valve 19a of the discharge mechanism 19 is opened, and the drain pump 19c is opened.
drive. As a result, the fuel pool water filled in the container body 15 flows out through the discharge pipe 19b of the discharge mechanism 19 and passes through the filter 19d.
and into the fuel pool. The container body 15 is now filled with air supplied by the pressure gas supply mechanism 17 . Then, the on-off valve 17b of the pressurized gas supply mechanism 17 is closed, and the compressor 17a is stopped. In this state, the high pressure jet pump 18a of the cleaning mechanism 18 is driven to supply water to the nozzle 1 via the cleaning water supply pipe 18d.
8c, high-pressure cleaning water is sprayed onto the fuel assembly 8 to clean it. At this time, the motor 16a of the drive device 16 is driven to move the fuel assembly 8 vertically or rotationally via the pulleys 16c, 16d and belt 16e. The rotation and vertical movement of the fuel assembly 8 causes the nozzle 18 of the cleaning mechanism 18 to
The high-pressure cleaning water sprayed from c hits the fuel assembly 8 uniformly, and the fuel assembly 8 is uniformly cleaned. In this case, since high-pressure cleaning water is sprayed in the air, this cleaning liquid collides with the fuel assembly at high speed, and the fuel assembly 8
The crud adhering to the surface of the cleaner is completely peeled off by the impact of the jet of cleaning water, resulting in a high cleaning effect. The cleaning water containing the crud accumulates in the lower part of the container body 15. When the crud is completely removed from the fuel assembly 8 , the high pressure jet pump 18a of the cleaning mechanism 18 is stopped to complete the cleaning. At this time, cleaning water containing the crud separated from the fuel assembly 8 is collected in the lower part of the container body 15 as described above. Therefore, the ejection mechanism 19
The on-off valve 19a is opened and the drain pump 19c is driven to discharge the cleaning water containing the crud accumulated in the lower part of the container body 15. The crud is then collected by the filter 19d and the remaining clean water is discharged into the fuel pool 5. Therefore, the inside of the fuel pool 5 is not contaminated. Next, the on-off valve 20b of the purification exhaust mechanism 20 is opened, and at the same time, the water supply pump 21a of the water supply mechanism 21 is driven, and the on-off valve 21b is opened. With this, the container body 1
The air inside 5 is passed through the exhaust pipe 20c of the purification exhaust mechanism 20.
and is exhausted through the filter 20a. The filter 20a completely removes the mist of radioactive substances contained in the exhausted air. Then, the container body 15 is filled with fuel pool water by the water supply mechanism 21 to equalize the pressure inside and outside the container body 15, and the lid 14 is opened to take out the cleaned fuel assembly 8. Note that the present invention is not limited to the above embodiment. For example, in the embodiment described above, the fuel assembly 8 is moved vertically or rotationally by the drive device 16 , but the fuel assembly 8 is fixed and the cleaning mechanism 1
Even if the No. 8 nozzle 18c is moved up and down or rotated, the same cleaning effect as in the previous embodiment can be obtained. The present invention can also be carried out by providing an on-off valve outside the container body instead of the water supply mechanism and opening the on-off valve when water is required to fill the container with water. Further, although pool water is used as the cleaning liquid in this embodiment, a special cleaning water liquid may be used to improve the cleaning effect. However, in this case, it is necessary to collect the cleaning liquid separately without releasing it into the fuel pool. As described in detail above, the fuel assembly cleaning device according to the present invention includes a container body provided in water in a fuel pool and accommodating a fuel assembly, a lid body provided on the container body and capable of being opened and closed, and the container body. A pressure gas supply mechanism connected to the main body and pressurized to supply gas into the container main body to discharge the water inside the container main body, and a cleaning nozzle inside the container main body, and applying high pressure to the fuel assembly through the cleaning nozzle. a fuel assembly cleaning mechanism that sprays a cleaning liquid; a cleaning liquid purification and discharge mechanism connected to the container body that discharges the cleaning liquid accumulated in the container body and collects and removes crud contained therein; a gas purifying and exhausting mechanism that purifies and exhausts the gas in the container body; and a water supply mechanism that is connected to the container body and supplies water into the container body when the gas in the container body is exhausted by the gas purifying and exhausting mechanism. It is characterized by the following: Therefore, since the cleaning liquid is sprayed onto the fuel assembly in a gaseous state, the jet stream hits the fuel assembly with an impact, and a sufficiently high cleaning effect can be obtained.
In addition, since the crud contained in the cleaning solution after this cleaning is collected by the purification and discharge mechanism, it is easy to recover this crud, and since this crud does not diffuse into the fuel pool, the entire fuel pool is contaminated. It will never happen. In addition, workers only need to remotely operate this cleaning device from a remote location, and since the main body of the container is located underwater in the fuel pool, the pool water provides sufficient radiation shielding, reducing the radiation exposure of workers. significantly reduced. Furthermore, since this container body is provided in the fuel pool water, radiation is shielded by the pool water, and the container body does not need to have a special radiation shielding structure, which simplifies its structure. Furthermore, the present invention is equipped with a gas purification exhaust mechanism and a water supply mechanism, and by activating these gas purification exhaust mechanism and water supply mechanism at the same time, the gas containing the radioactive material mist inside the container body is completely removed. It can be purified and released as clean air.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing the schematic structure of fuel handling equipment and surrounding areas in the upper part of the core of a boiling water reactor; FIG. 2 is a partial cross-sectional view showing the schematic structure of an embodiment of the present invention; FIG. 3 is a longitudinal sectional view showing an embodiment of the present invention in more detail than FIG. 2, and FIG. 4 is a plan view of the inside of the container main body viewed from above. 5...Fuel pool, 8...Fuel assembly, 14...
...Lid body, 15 ... Container body, 17 ... Pressurized gas supply mechanism, 18 ... Fuel assembly cleaning mechanism, 19 ...
Cleaning liquid purification and discharge mechanism, 20 ...Gas purification and exhaust mechanism.

Claims (1)

[Claims] 1. A container body which is provided underwater in a fuel pool and accommodates a fuel assembly, a lid body which is provided on this container body and can be opened and closed, and which is connected to the container body and which supplies gas under pressure into the container body. a pressure gas supply mechanism for discharging internal water; a fuel assembly cleaning mechanism having a cleaning nozzle in the container body and spraying a high-pressure cleaning liquid onto the fuel assembly through the cleaning nozzle; a cleaning liquid purification and discharge mechanism connected to the container body to discharge the cleaning liquid accumulated in the container body and to collect and remove crud contained therein; and a gas purification and exhaust mechanism connected to the container body to purify and exhaust the gas in the container body. A cleaning device for a fuel assembly, comprising: a water supply mechanism that is connected to the container body and supplies water into the container body when the gas in the container body is exhausted by the gas purification/exhaust mechanism.