JPS623918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotary plug seal in a fast breeder reactor or the like, and particularly to a rotary plug seal suitable for preventing cover gas leakage.

In general, a low melting point alloy (freeze seal alloy, hereinafter referred to as seal alloy) is used for shielding plugs in liquid metal cooled nuclear reactors such as fast breeder reactors to seal against leakage of reactor cover gas to the outside of the reactor. A freeze seal mechanism is provided as one of the rotating plug seals.

The conventional freeze seal mechanism consists of a dam 2 attached to a rotating plug 1 and a dam 2 as shown in FIG.
A heater 3 arranged inside, a freeze metal bucket 6 which houses the seal alloy 5 attached to the fixed plug 4 and into which the lower part of the dam 2 is immersed, and a heater 3 arranged on the outer periphery of the freeze metal bucket 6 and inside as shown in FIG. As shown, it is composed of a cooling channel 7 having partitions 7a arranged vertically alternately in the circumferential direction, and when replacing fuel, the seal alloy 5 is melted by a heater 3 so that the rotary plug 1 can be rotated. During furnace operation, a refrigerant such as nitrogen gas is passed through the cooling channel 7 as shown by the arrow in FIG. 2 for forced cooling, thereby freezing the sealing alloy 5 and sealing it.

In the conventional freeze seal mechanism explained above,
A perfect seal can be expected when the seal alloy 7 is molten, but a perfect seal cannot be expected when it is frozen.

That is, in the freezing process of the seal alloy, it is said that it is best to freeze from the bottom and proceed to the top while compensating for the shrinkage during freezing. However, if a refrigerant such as nitrogen gas is allowed to flow through the cooling channel 7 in the circumferential direction, the seal alloy 5
In the conventional cooling method of freezing, the temperature is lowered from the freeze metal bucket 6 side, and in the axial direction, the freeze metal bucket 6 is attached to the fixed plug 4, so the temperature is lower at the top than at the bottom. Become. Therefore, during the freezing process, there is a risk that the sealing alloy 5, the dam 2, and the freeze metal tub 6 may peel off at the adhering portions, or cracks may occur in the blowholes, causing the cover gas inside the furnace to leak to the outside.

In addition, when natural cooling is performed without forced cooling using a refrigerant, there are problems such as a long freezing time, which is disadvantageous in terms of plant operation rate.

The present invention was devised to solve these conventional problems, and its purpose is to provide a rotating plug seal that does not leak cover gas even when forced cooling is performed.

The present invention focuses on the fact that the conventional difficulty is that the seal alloy freezes from the upper side, and uses a cooling mechanism to cool down the bottom side of the frozen metal tub, thereby causing the seal alloy to freeze. The freeze progresses from the bottom side to the top side.

The present invention will be explained below based on an embodiment shown in FIGS. 3 to 5.

Figure 3 shows a liquid metal cooled nuclear reactor.
In the figure, 11 is a rotating plug. The rotating plug 11 is eccentrically arranged within the fixed plug 14, and forms a shielding plug together with the fixed plug 14. As shown in the figure, this shielding plug is installed at the upper part of the reactor pressure vessel 8, and performs a shielding function and a sealing function against heat and radiation from inside the reactor against the upper part of the reactor.

Inside the reactor pressure vessel 8, as shown in FIG. 3, a reactor core 9 is housed, and a coolant is filled, and there is a gap between the coolant liquid level A and the lower surface of the shielding plug. is injected with an inert gas such as argon gas to form a cover gas space. This cover gas is prevented from leaking out of the furnace by a freeze seal mechanism 10 provided between the rotating plug 11 and the stationary plug 14, as shown in FIG.

As shown in FIG. 4, the freeze seal mechanism 10 includes a dam 12 attached to a rotating plug 11, a heater 13, a seal alloy 15, a freeze metal tub 16 attached to a fixed plug 14, and the like.

The dam 12 is formed into a ring shape with an inverted L-shaped cross section as shown in FIG.
3 are arranged. And this dam 12 is
Ring-shaped frozen metal bucket 16 with a groove-shaped cross section
The lower end portion is immersed in a sealing alloy 15 housed in a freeze metal tub 16.

As shown in FIG. 4, the freeze metal tub 16 has a hollow side wall, and inside thereof, as shown in FIG.
A partition plate 18 that divides the cooling channel 17 into a plurality of parts in the circumferential direction, buttfuls 19 stacked on the left and right alternately in the axial direction so that the refrigerant flows through them in the axial direction; Connecting studs 20 that integrate the buttfuls 19 of the
It is fixed to the connecting stud 20 by a hexagonal nut 21 screwed onto the connecting stud 20. In the chamber 22, which is partitioned vertically by the vertical part 19 at the lower end, there is a fifth
As shown in the figure, an air supply pipe 23 protruding from the freeze metal tub 16 is communicated with the air supply pipe 23 and a chamber 24 partitioned vertically by a buttful 19 at the upper end.
Exhaust pipe 2 protruding from similarly frozen metal bucket 16
5 are connected. The air supply pipe 23 and the exhaust pipe 25 are each connected to a cooling device (not shown).

In the above configuration, the refrigerant supplied from the air supply pipe 23 to the cooling channel 17 enters the chamber 22 as shown in FIG. While doing so, it rises and enters room 24. and exhaust pipe 25
is discharged from.

As explained above, this embodiment provides the following effects.

(1) Since the refrigerant flows through the bottom of the freeze metal bucket, the temperature of the freeze metal bucket is low at the bottom and high at the top, resulting in a temperature gradient where the seal alloy solidifies from the bottom and freezes up.
Therefore, peeling or cracking due to shrinkage during freezing does not occur, and leakage of cover gas can be effectively prevented.

(2) Freeze time can be shortened by forced cooling, which can improve plant operation rate.

The present invention has been described above based on preferred embodiments, but according to the present invention, there is no leakage of cover gas even by forced cooling.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional example, FIG. 2 is a sectional view taken along the - line in FIG. 1, FIG. 3 is a sectional view of a reactor pressure vessel, and FIG. 4 is a sectional view showing an embodiment of the present invention. ,
FIG. 5 is a sectional view taken along the line -- in FIG. 4. 11...rotating plug, 12...dam, 13...
Heater, 14... Fixed plug, 15... Seal alloy, 16... Freeze metal tub, 17... Cooling channel.

Claims (1)

[Claims] 1. A rotating plug seal for a nuclear reactor, in which a freeze metal bucket in which freeze metal is stored is disposed between a rotating plug and a stationary plug, and the freeze metal is cooled and solidified to seal between the rotating plug and the stationary plug. A rotary plug seal characterized in that a plurality of buttfuls are stacked in the axial direction in a freeze metal tub so that a flow path is formed between the buttfuls from the lower part to the upper part.