JPS5833191A - Method of preventing radioactivity contamination of bellows for exchanging fuel in bwr type reactor container - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure in which a bellows for fuel exchange and a reactor well seal bellows are kept from coming into contact with contaminated water during water exchange during fuel exchange.

The reactor containment vessel is a vessel that houses the reactor secondary cooling system, such as the reactor pressure vessel, recirculation pump, and piping.In the unlikely event that a rupture occurs in the secondary cooling system, a loss of coolant accident may occur. They are installed to prevent radioactive materials that could be released from the core from dispersing to the outside even in the event of a nuclear accident, and therefore require an extremely reliable design.

The method for fixing the BWR type reactor containment vessel and the reactor pressure vessel within this vessel is a one-end support structure in which only the bottom is fixed due to earthquake resistance, heat resistance, and architectural installation issues.

In other words, in the reactor containment vessel, the bottom is fixed to the foundation concrete mat with anchor bolts, and the top and surrounding area are shielded by a shield wall with gaps, and in the reactor pressure vessel, the bottom is fixed to the foundation of the reactor body. It is fixed with anchor bolts, and the upper part and surrounding area are unrestricted.

However, when replacing fuel in the reactor pressure vessel, Minamata, Therefore, the gap between the shield wall and the reactor containment vessel should be constructed with a flexible, eccentric, flexible structure in each gap, taking into consideration the earthquake resistance, heat resistance, and architectural installation issues mentioned above. It uses a bellows made of thin, corrugated stainless steel.

However, the crud inside the reactor pressure vessel becomes floating matter during clean-up operation after filling with water and adheres to the bellows corrugated portion, remaining even after water is drained, increasing the radiation level.

Therefore, it was necessary to take measures regarding this.

The present invention prevents floating matter such as dust from adhering to the corrugated portion of the bellows by installing a force/bar all around the upper part of the bellows to cut off the water near the bellows and the water used to fill the tank at the time of fuel exchange. This is to prevent

FIG. 1 is a longitudinal sectional view showing a part of the structure of a BWR, MARK-It type frozen reactor containment vessel.

1 is the reactor pressure vessel, and in consideration of earthquake resistance, thermal expansion, installation, etc., only the lower part is fixed with anchor bolts, and the upper part is fixed with bolts. .

3 is the reactor containment vessel, and as mentioned above, only the lower part is fixed to the base concrete 1 notebook mat with anchor bolts, and the upper part is fixed with bolts to the top head of the 4 reactor containment vessel, which is opened at the time of fuel exchange and periodic inspection.

Figure 2 shows the top head of two reactor pressure vessels and the top head of four reactor containment vessels removed and filled with water to prevent exposure to radiation during fuel exchange.

3 shows the bellows portion between the reactor pressure vessel and the reactor containment vessel and between the reactor containment vessel and the 7-ruby wall in a detailed view of part A in FIG. 2, which has a conventional structure.

The bellows structure in the conventional structure will be explained below with reference to FIG.

9 is a fuel exchange bellows between the reactor pressure vessel 1 and the reactor containment vessel 3, and 10 is a seal well bellows between the reactor containment vessel and the Nord wall 11. Bellows protective covers 13 and 15 are mounted on cover mounting seats 14 and 16 on each inner diameter can. Since the protective covers 13 and 15 are attached with a gap between the upper part and the circumferential joint, the bellows is completely immersed in water when filling with water during fuel exchange. Therefore, over a long period of time, the crud inside the pressure vessel becomes floating matter when filled with water, and like the above-mentioned dust, it adheres to the bellows 9.10, cover 13.15, etc.

However, since the bellows 9 and 10 are required to be flexible and eccentric, they have a plurality of corrugated shapes.
It remained even after water was drained on July 18th, increasing the amount of radiation.

For this reason, decontamination work such as washing with water is required, but as mentioned above, since it has a plurality of corrugated shapes, there are problems in that the work is not only difficult but also ineffective.

Fig. 4 is a detailed view of part A in Fig. 2 according to the present invention, and the conventional structure 3.
The difference from the diagram is that there is a cover 19.2 that covers the entire upper circumference of bellows 9 and 10 to shield the bellows chamber from water during fuel exchange.
This is a structure in which 0 is installed.

According to the present invention, at the time of Minamata such as fuel exchange, after the chambers a and b near the bellows are first filled with water, the covers 19 and 20 are installed on the upper part of each bellows, and then the bellows 9 and 10 are filled with water for fuel exchange. The cover 19.20 blocks floating matter such as high-dose crud dust from the pressure vessel, preventing it from adhering to the bellows 9.10 and increasing the radiation concentration.

According to the present invention, decontamination work, inspection work inside the containment vessel, etc. can be easily carried out without changing the bellows structure from the conventional one, and there is an advantage that countermeasures can be easily taken because only a cover is attached to an existing plant.

[Brief explanation of the drawing]

Figure 1 is a vertical sectional view of the reactor containment vessel, Figure 2 is a view of the top head area of Figure 1 during fuel exchange, Figure 3 is a detailed view of section A in Figure 2, showing the conventional structure, Figure 4 2 is a detailed view of part A in FIG. 2 according to the present invention. DESCRIPTION OF SYMBOLS 1... Reactor pressure vessel, 2... Reactor pressure vessel top head, 3... Reactor containment vessel, 4... Reactor containment vessel top head, 5... Reactor body foundation, 6・・・
・Diaphragm floor-17...Pool water, 8...
Vent pipe, 9... Bellows for fuel exchange, lO... Seal well bellows, 11... Shield wall, 1
2... Foundation concrete, 13... Bellows protective cover, 14... Cover mounting seat, 15... Bellows protective cover, 16... Cover mounting seat, 17.18...
Drain, 19.20 chopsticks l 躬 2nd strategy 3 Figure 14 Figure

Claims (1)

[Claims] 1. At the time of fuel exchange in a BWR type nuclear power plant, the area near the reactor well seal bellows or fuel exchange seal bellows is sealed, and then a cover with a sealing effect is installed at the upper end around the entire circumference. A method for preventing radioactive contamination of bellows for fuel exchange, which is characterized by the use of Minamata.