JPS6312277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to, for example, a shielding plug for a fast breeder reactor that uses liquid metal as a coolant, and particularly relates to a nuclear reactor shielding plug that improves the method of fixing a rotating plug during reactor operation. .

The shield plug for fast reactors is located at the top of the reactor vessel and has a structure that rotates in single, double, or triple rotations while maintaining radiation and heat shielding functions and maintaining airtightness for fuel exchange. has been widely adopted. Among the flexible plugs, the above-mentioned rotating plug is called a rotating plug, and the stationary part is called a fixed plug. This rotating plug usually uses the following method in order to rotate with the necessary precision while maintaining the necessary airtightness during fuel exchange, and to maintain the necessary airtightness in a stationary state during reactor operation. .

(a) A low melting point metal seal is used as the rotating part seal, and this metal seal is in a molten state when the rotating plug rotates, and is in a solidified state during reactor operation.

(b) If necessary, use an elastomer seal as a backup for the metal seal.

(c) Use ball bearings to improve turning accuracy. In order to alleviate the load conditions on the ball bearing, when the rotary plug is turned, the rotary plug is lifted by a hydraulic lifting device or the like so that the entire load of the rotary plug is applied to the ball bearing.

(d) During reactor operation, the rotating plug is placed directly on the fixed plug without using ball bearings, and measures are taken to prevent it from tipping over.

When adopting the above method, there is room for improvement in the following points if an earthquake occurs during reactor operation.
Improvement measures were desired.

(1) Although the above (d) prevents the entire rotating plug from falling over, there is a possibility that the rotating plug may move horizontally by the gap between it and the fixed plug. In order to reliably scram the control rods, it is necessary to include this horizontal movement in the design, making the design to ensure the control rod scram function even more ingenious.

(2) During reactor operation, the low melting point metal of the rotating plug seal is in a solidified state, so when the rotating plug moves horizontally as described in item (1), this low melting point metal seal section is forcibly displaced. Since the contact state between the forcing member and the seal metal changes, there is a risk that the sealing performance during an earthquake will change.

The present invention was made in view of the above circumstances, and
An object of the present invention is to provide a nuclear reactor shielding plug that can stably hold a rotating plug even when vibrations such as earthquakes occur.

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

FIG. 1 is a longitudinal sectional view of a nuclear reactor shielding plug according to the present invention. In this figure, a reactor vessel 1 is supported and held at its upper end by a support structure 20 of the reactor. The reactor shield plug, which serves as the lid of the reactor vessel 1, has a schematic structure including a fixed plug 2 fixed to the upper edge of the reactor vessel 1, and a fixed plug 2 that is fitted into the fixed plug 2 and inserted through the reactor. It consists of a rotating plug 3. A core upper mechanism 4 is provided passing through this rotating plug 3, and this rotating plug 3 includes a rotating plug upper plate 31 which is a main strength member, and a rotating plug located below this rotating plug upper plate 31. It consists of a lower plate and a rotary plug riser 32 fixed to the upper edge of a rotary plug upper plate 31.

A large gear 7 is mounted on the rotary plug riser 32, and the large gear 7 can be rotated via a small gear 9 attached to a rotational drive mechanism 10 provided on the fixed plug 2. It's summery. Also, on top of the large gear 7 is a hydraulic lifting device 8.
is attached to the rotary plug riser 32.
The rotary plug is configured to be pulled up via the rotary plug. The fixed plug 2 has a cylindrical support member 2.
1, and a large gear 7 via a ball bearing 6
It is designed to be able to support the supporting member 2.
1 is provided with an annular tank 22 capable of receiving a low melting point alloy seal 5. A cylindrical partition plate 23 provided on the outside of the rotary plug riser 32
The rotating plug 3 and the stationary plug 2 are kept airtight by being immersed in the low melting point alloy seal 5 stored in the annular tank 22.

As shown by symbol A in FIG. 1 and enlarged in FIG. 2, a guide blade 33 is provided in an annular shape protruding from the lower peripheral edge of the rotary plug upper plate 31 constituting the rotary plug 3. ing. Further, a guide slit 21, which is a circular groove-shaped recess, is provided on the upper surface of the fixed plug 2 at a portion that comes into contact with the guide blade 33.

The operation of the nuclear reactor shield plug according to the present invention configured as described above will be explained.

When the hydraulic lifting device 8 provided on the large gear 7 is activated to lift the rotary plug 3 during reactor shutdown, a guide blade 33 protruding from the lower part of the rotary plug upper plate 31 and a guide blade 33 provided on the upper surface of the fixed plug are activated. The guide slit 21 is separated. Therefore, no resistance force against the rotational moment of the rotating plug 3 is generated at this location. The rotary plugs supported by the ball bearing 6 are rotated by the rotary drive mechanism 1.
0, it is rotated via the large gear 7 and the small gear 9. Then, the core upper mechanism 4 attached to the rotary plug 3 is positioned at a predetermined position in the reactor vessel, and the reactor core upper mechanism 4, which is attached to the rotary plug 3, is positioned at a predetermined position within the reactor vessel 1 to perform operations such as replacing fuel rods in the reactor core (not shown) installed in the reactor vessel 1. do the work.

On the other hand, when starting up the reactor, the hydraulic lifting device 8
is activated to lower the rotating plug 3. Then, the guide blade 33 moves into the guide slit 2.
The rotary plug 3 is inserted into the fixed plug 2 and fitted, and the rotary plug 3 is placed on and supported by the fixed plug 2. That is, as a result of the guide blade 33 and the guide slit 21 being fitted together, the relative positions of the fixed plug 2 and the rotating plug 3 will not shift even if vibrations such as an earthquake occur.

In the described embodiment, the rotating plug is provided with a convex guide blade and the fixed plug is provided with a concave guide slit, but conversely, the fixed plug is provided with a convex guide blade and the rotating plug is provided with a concave guide slit. It is also possible to have a configuration in which a guide slit is provided. Further, the guide blade does not necessarily have to be annular, and may have a configuration in which convex blocks are arranged on the circumference.

As explained above, the reactor shielding plug according to the present invention can prevent the relative movement of the rotating plug upper plate 31 with respect to the fixed plug 2 even if an earthquake occurs during reactor operation, and as a result, the control rod scram function is achieved. Maintenance ability can be improved. In addition, since no forced displacement is applied to the low melting point alloy seal portion, sufficient structural strength can be maintained without generating large stress on the cylindrical partition plate, etc., and the contact state between the cylindrical partition plate etc. and the low melting point alloy seal 5 does not change. Can maintain stable sealing function.

Furthermore, since the guide blade 33 and the guide slit 21 part are engaged, this part acts as a gas flow resistance part, and even if the reactor cover gas pressure fluctuates rapidly, the pressure fluctuation will be suppressed by the rotating plug seal. Since it is not directly transmitted to the low melting point alloy seal 5 but is transmitted in a relaxed manner, the sealing performance of the rotating plug becomes even more stable.

Furthermore, it is possible to almost completely prevent the sodium vapor generated from the sodium stored in the reactor vessel from migrating to the low melting point alloy seal 5 portion, thereby suppressing the performance deterioration of this alloy seal.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a nuclear reactor shielding plug according to the present invention, and FIG. 2 is a vertical cross-sectional view showing an enlarged guide blade portion (section A) in FIG. 1. 1...Reactor vessel, 2...Fixing plug, 3...
Rotating plug, 31... Rotating plug upper plate, 5... Low melting point metal seal, 21... Guide slit, 33
...Guide blade.

Claims (1)

[Scope of Claims] 1. In a flexible plug that closes an upper opening of a reactor vessel and is composed of a fixed plug and a rotating plug inserted through the fixed plug, a circumferential portion is provided on the lower surface of the rotating plug. What is claimed is: 1. A nuclear reactor shielding plug, characterized in that the fixing plug is formed with a convex portion, and a circular groove-shaped concave portion that fits into the convex portion is formed in the fixed plug. 2 Forming a circular groove-shaped recess on the lower surface of the rotating plug,
Claim 1, characterized in that a convex portion that fits into the concave portion is formed on the upper surface of the fixing plug.
Nuclear reactor shield plug as described in section.