JPS5936239B2 - Cleaning method inside the lower reactor chamber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning the lower chamber of a nuclear reactor, and particularly to a method for cleaning the lower chamber of a nuclear reactor, which is suitable for reducing radiation exposure during regular inspections of nuclear power generation equipment. .

Generally, during periodic inspections, replacement of control rod drives and local power range monitors is carried out inside the lower reactor chamber, so reactor water containing radioactive materials may leak onto the floor, etc.
When this is concentrated and accumulated, the working atmosphere becomes a high radiation level.

For this reason, conventionally, workers regularly spray water on them with a hose to clean them.

However, in this cleaning method, the radiation level increases in proportion to the length of time until the next decontamination work, and the radiation exposure of workers who continuously work inside the lower reactor chamber increases.

In order to solve this problem, decontamination can be carried out frequently, but this is not preferable because, for example, workers dedicated to decontamination would be exposed to increased amounts of radiation on their bodies.

An object of the present invention is to provide a method for cleaning the inside of a lower reactor chamber that can reduce radiation exposure caused by reactor water to workers replacing control rod drive devices in the lower chamber of the nuclear reactor.

The cleaning method of the present invention involves replacing a control rod drive device in a lower reactor chamber by using a spray header having a spray nozzle that sprays cleaning water onto the side walls and floor surfaces of the lower reactor chamber, each of which has a lined surface. The spray nozzle is installed near the side wall of the location, and before the replacement work of the control rod drive device starts, that is, before the reactor water gets attached, cleaning water is sprayed from the spray nozzle to form a thin film of water on the side wall and floor surface, and then Further, during or after the replacement work of the control rod drive device, cleaning water is again sprayed from the spray nozzle to clean the side walls and floor surface.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a lower reactor chamber showing an embodiment of the present invention, and FIG. 2 is a detailed view of section A in FIG. 1.

In these diagrams related to the lower chamber of a boiling water reactor, 10
1 is a nuclear reactor, 11 is a reactor pressure vessel, and 12 is a housing in which a control rod drive device 13 is housed.

20 is the reactor lower chamber, 21 is the side wall, 22 is the floor, 23
is a drain funnel, and 24 is a lining.

30 is a pit, 31 is a pump, 32 is a purifier, 33 is an agitator, and 34 is a cooler.

40 is a spray header, 41 is a spray nozzle, 42 is a drain hole, and 43 is a water supply pipe.

In other words, in a boiling water reactor, fuel, control rods,
A nuclear reactor 10 consisting of reactor internals, reactor water, etc. is housed in a reactor pressure vessel 11, and a housing 12 housing a control rod drive device 13 is located at the bottom of the reactor pressure vessel 11.
is installed in contact with reactor water.

Replacement work of the control rod drive device 13 during periodic inspections, ie, its removal and installation after overhaul, is performed within the reactor lower chamber 20.

At that time, reactor water leaking from the control rod drive device 13 and the flange portion of the housing 12 flows onto the side wall of the lower reactor chamber 20.
1, the floor surface 22, etc.

In order to remove this adhered reactor water, a spray header 40 is provided with a plurality of spray nozzles 41 that spray cleaning water onto the side 21 and floor 22 of the lower reactor chamber 20.
is provided at the replacement work position of the control rod drive device 13 in the lower reactor chamber 20 and close to the side wall 21 .

This spray header 40 is installed at a higher position than the area where the reactor water that leaks out when the control rod drive unit 13 is replaced is scattered and adheres to the side wall 21, so that the spray water can sufficiently remove the reactor water that has adhered to the side wall 21. It is necessary to cover the

A drain funnel 23 is provided on the floor surface 22, and the cleaning wastewater flowing into this drain funnel 23 is
It is guided outside the reactor lower chamber 20 and collected in the pit 30.

This pit 30 is provided with an agitator 33 that stirs the sludge that accumulates at the bottom of the pit, and a cooler 34 that cools the washing wastewater when it is hot water, and sends the washing wastewater to a purification device 32 or wastewater treatment equipment. A pump 31 is provided.

3 purification device 32 is a device for removing radioactive materials from cleaning wastewater, and the cleaning wastewater from which radioactive materials have been removed is sent to the water supply pipe 43 as cleaning water and can be recirculated.

When operating the cleaning device configured as described above, it is important to spray cleaning water onto the side wall 21 and the floor surface 22 before starting to remove the control rod drive device 13.

By forming a thin film of water on the surface of the lining 24 due to the wetting phenomenon before the reactor water adheres to the surface, when the control rod drive device 13 is replaced, water may be scattered or dropped onto the side wall 21 or the floor surface 22 and adhered thereto. The reactor water is diluted by the thin film of water, and during cleaning, the reactor water is
Automatically drains out of the outdoor pit 30 from the drain funnel 23 without remaining in the water and is collected.

Therefore, the working environment inside the reactor lower chamber 20 has a significantly low radiation level.

In addition, in the present invention, the side wall 21 of the lower reactor chamber 20
and surface 22. Not only that, but also.

Drain funnel 23 and the drain funnel 2
It is also possible to line the pit 30 including the flow path from the pipe 3.

Stainless steel is the most preferred lining.

This prevents reactor water from penetrating into the concrete, further improving the effect of reducing radiation exposure.

As described above, according to the cleaning method of the present invention, during work such as periodic inspection, the interior of the room is sprayed with cleaning water in advance to wet the side walls and floor surface, and then the control rod drive device is sprayed with cleaning water. Since the workers enter the room after replacing the reactor and performing spray cleaning, the radiation exposure caused by the reactor water to workers inside the room is extremely reduced, and the effect of improving safety is significant.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of a lower reactor chamber of a boiling water nuclear reactor showing an embodiment of the present invention, and FIG. 2 is a detailed view of section A in FIG. 1. 10... Nuclear reactor, 11... Reactor pressure vessel, 12... Housing, 13...
Control rod drive device, 20... Reactor lower chamber, 21
...Side wall, 22...Floor surface, 24...
...Lining, 30...Pit, 32...
...Purification device, 40...Spray header,
41...Spray nozzle, 43...Water supply pipe.

Claims (1)

[Scope of Claims] 1. A spray header having a spray nozzle that injects cleaning water onto the side walls and floor surfaces of the lower reactor chamber, each of which has a lining, is connected to the control i vehicle drive unit of the lower reactor chamber. The spray nozzle is installed near the side wall of the replacement work location, and before the replacement work of the control rod drive device starts, cleaning water is sprayed from the spray nozzle to form a thin film of water on the side wall and floor surface. A method for cleaning the inside of a lower reactor chamber, characterized by spraying cleaning water from the spray nozzle again to clean the side walls and floor surface during or after the replacement work. 2. The side walls and the floor surface are made of stainless steel. A method for cleaning a lower chamber of a nuclear reactor according to claim 1, wherein the lining is applied to a lower chamber of a nuclear reactor.