JPS5836320B2 - Genshironiokel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing accumulated activation sludge in a housing for a control rod drive device and a neutron monitoring device of a nuclear reactor.

In a nuclear reactor, primary cooling water is circulated within the reactor by a circulation pump, and the steam generated at this time is sent to a turbine to generate electricity.

However, it is difficult to completely eliminate the sludge in the primary cooling water, so if the operation continues, radioactive sludge with a high radioactivity level will accumulate in water pools in the reactor.

For example, in a nuclear reactor, a control rod drive device called CHD and a neutron monitoring device called PRM are housed and installed in a housing provided at the bottom of a pressure vessel containing the reactor core to control output, etc., but the housing is used for primary cooling. As water stagnation is formed, sludge in the primary cooling water, ie, a high level of activated sludge, accumulates within the housing.

Therefore, when the reactor is shut down during periodic inspections, even after the radioactivity level of the primary cooling water has decreased, a high level radiation source remains due to the accumulated sludge, so it is necessary to inspect and replace the control rod drive device etc. This requires advanced radiation protection for workers, and it is difficult to work for long periods of time due to limitations on the amount of radiation the human body can be exposed to.

Therefore, when 10 to 30 rods need to be replaced during periodic inspections, such as in the case of a control rod drive device, it takes an extremely long time, and work efficiency cannot be improved.

The present invention has been made in view of the above points, and provides a simple and quick method for removing hard-to-remove radioactive sludge accumulated in the housing of a control rod drive device, etc., and rapidly reduces the radioactivity level in the working environment. This is designed to reduce the amount of damage caused and improve work efficiency.

Next, a detailed explanation will be given using the drawings. In addition to the primary cooling water system that circulates and cools the inside of the reactor as described above, the nuclear reactor has a purified water system that extracts a portion of the primary cooling water, purifies it, and then retransmits it into the reactor.

The present invention operates the circulation pump of the primary cooling water system and the recirculation pump of the purified water system before starting the inspection work of each part after the reactor is shut down, and stores a part of the cooling water purified by the purified water system. The housing housing and control rod can be accessed through the water injection hole provided on the bottom side of the housing. This removal method is characterized by injecting water into the gap between the sludge and the drive device, and using the strong water flow to wash and remove the accumulated sludge, return it to the primary cooling water circulating in the furnace, and send it to the purified water system.

Fig. 1 is a system diagram of one embodiment of the present invention applied to the removal of accumulated sludge in a housing housing such as a control rod drive device;
Figures a and b are cross-sectional views of a control rod drive device modified to implement the present invention and a housing housing for a neutron monitoring device.

In Fig. 1, 1 is a reactor core, 2 is a pressure vessel, and 3 is a housing for housing control rod drive devices, etc., and this housing has a cylindrical body 3b with a water injection hole 3a in its lower part as shown in Figs. 2a and b. It is fixed through the bottom part 2a of the pressure vessel 2 of the furnace.
After inserting the control rod drive device 4 or the neutron monitoring device 5 through the lower opening, for example, the flange portion 3c provided at the lower end of the cylindrical body 3b is attached to the flange portion 4a or 5a provided at the lower end of the drive device, etc. It is shaped so that it can be connected watertightly and can be replaced and inspected.

In addition, in order to prevent the primary cooling water in the pressure vessel from being discharged to the outside through the housing when the control rod drive device, etc. is pulled out from the housing, the drive device is removed at the top of the cylindrical body 3b forming the housing. A valve (not shown) that operates in conjunction with the cylindrical body is provided to automatically close the upper end opening of the cylindrical body when the cylindrical body is pulled out.

Returning to Figure 1, 6 is a circulation pump, 7 is piping, 8 is a valve, 9
1 is the drain valve, 10 is its upper pipe, and 1
Next, a cooling water system is used to circulate and cool the inside of the reactor, and the steam generated at this time is guided to a turbine (not shown) through a pipe 11 provided at the upper part of the pressure vessel 2 to generate electricity.

12 is a purifier, 13 is a recirculation pump, 14 is piping, 15
is a valve, 16 is a cleaning valve, 17 is its piping, 18 is a drain valve, and 19 is a purified water supply valve, these form a purified water system,
After a portion of the primary cooling water is extracted from the bottom of the pressure vessel 2 and purified, it is re-sent into the pressure vessel 2 via the purified water supply valve 19, the water supply valve 20, and the water supply piping 21.

A portion of the purified water is also connected to a water injection hole 3a provided at the lower part of the housing nozzle 3 via a cleaning valve 16 and a pipe 17.

Note that 22 is a water supply regulating valve.

Therefore, as mentioned above, before starting the inspection work,
When the primary cooling water is circulated in the reactor and the recirculation pump 13 is used to purify the primary cooling water, if the valve 19 is appropriately throttled and the valve 16 is opened, the purified 1
A portion of the next cooling water is injected into the lower part of the accommodation housing 3 through the water injection hole 3a, creating a strong water flow from the accommodation housing 3 into the furnace as indicated by the arrows shown in FIGS. 2a and 2b.

Therefore, the sludge accumulated in the accommodation housing 3 is washed away by the above-mentioned strong purified water flow, returns to the primary cooling water circulating in the furnace, and is purified by the purified water system.

Therefore, if this work is continued for the required time, the radioactivity level in this area can be rapidly reduced, and the replacement and inspection work of the control rod drive device etc. can be carried out quickly after the reactor is shut down.

That is, according to the present invention, workers can be avoided from dangerous direct work by providing an injection hole in the accommodation housing5 and by modifying simple equipment such as piping and valves for branching purified water. Since the removed sludge is also treated by the purified water filter, it is less dangerous and easier to treat than a separate treatment method that involves direct work by workers.

Although the present invention has been described above with reference to one embodiment, it is also possible to inject a two-phase fluid of purified water and a gas such as nitrogen gas to ensure faster removal.

As is clear from the above explanation, according to the present invention, the activated sludge deposited in the primary cooling water system of a nuclear reactor can be easily and quickly removed, and the working environment during inspections can be improved. This has great practical effects.

[Brief explanation of drawings]

Figures 1 and 2a and 2b are a system diagram of an embodiment of the present invention for removing sludge in a housing housing for a control rod drive device and a neutron monitoring device, and a structural example diagram of a housing housing for carrying out the present invention. be.

Claims (1)

[Claims] 1 Before inspection work after reactor shutdown, the circulation pump of the primary cooling water system and the recirculation pump of the purified water system are activated, and a portion of the primary cooling water purified by the purified water system is transferred to the control rod drive device. Activated sludge deposited in a nuclear reactor is injected from the bottom into a housing housing of a neutron monitoring device and discharged into a primary cooling water system, and the deposited sludge washed and removed at that time is purified by a purified water system. Removal method.