JPS6239915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealing structure for a nuclear reactor plug that uses a liquid sealant to seal between a fixed plug and a rotating plug that close the opening of a container in a fast reactor. The upper reactor plug in a fast reactor closes off the upper part of the reactor vessel, and is used to install the control rod drive mechanism, fuel exchanger, etc., and consists of a fixed plug and a rotating plug.

That is, the rotary plug has a control rod drive device located on the center line of the reactor vessel, and is also equipped with a fuel exchanger at an eccentric position, and when exchanging the fuel, the control rods are removed from the control rod drive device into the reactor core, and the control rods are moved into the reactor core. The control rods are transferred to the fuel storage area surrounding the reactor core by rotating the rotary plug while the power is reduced and using the refueling machine.

Therefore, the rotary plug is rotatably fitted into the fixed plug provided in the opening of the furnace vessel. This rotating plug and the furnace vessel require a strict seal to prevent leakage of the cover gas inside the furnace.
Conventionally, this seal structure uses a liquid sealing material.

That is, a gutter-shaped saucer (also referred to as a bucket) containing a liquid sealing material, which will be described later, is formed around the entire circumference of either the inner circumference of the fixed plug provided at the opening of the furnace vessel or the outer circumference of the rotating plug. At the same time, a partition plate is formed around the entire circumference on the other side to be immersed in the liquid seal in the saucer, and the airtightness inside the furnace vessel is maintained by the partition plate and the liquid seal material.

The above-mentioned liquid sealing materials include metals such as mercury that become a solution at room temperature, or metals that solidify (freeze) at room temperature, such as Bi-Sn alloys with low melting points, but go into solution at a temperature of 100 to 150°C. Freeze seal metal or liquid seal material is used.

The latter liquid sealing material is used to maintain a solidified state during furnace operation or when the rotary plug is not rotating, and only when the rotary plug is rotated, it is heated with a heater and turned into a solution, allowing movement of the partition plate. There is.

However, with this freeze seal structure, if the cover gas pressure in the furnace fluctuates while the liquid sealant is in solution, the liquid level of the liquid sealant in the tub oscillates in response to the gas pressure, causing the gas pressure to fluctuate. When the pressure is extremely large, for example when the cover gas pressure is low, the liquid level of the sealant drops to the lower end of the partition plate and other gases suddenly blow through to the cover gas side.

Therefore, the liquid level fluctuation (on the cover gas side) of the other liquid sealing material increases, causing a problem that the liquid sealing material overflows from the tub and jumps into the furnace vessel. When liquid sealant overflows into the reactor vessel, it contaminates the cover gas and cooling fluid, changes the thermal and nuclear properties of the fluid, causes corrosion of structural materials, and also precipitates as impurities that flow away. There is a risk that the road will be blocked.
For this reason, it is necessary to remove the liquid sealing material, which has the drawback of requiring an extremely large amount of labor. Additionally, if the gas pressure inside the reactor vessel fluctuates beyond the normal control range while keeping the liquid sealant in a heated and molten state, the liquid sealant will
There is a risk of overflowing from the sealing tub and spouting into the reactor vessel or outside the shielding plug. In particular, if the liquid sealant spews out inside the reactor vessel and mixes into the reactor coolant, it is undesirable because it may cause unexpected blockage, change in melting point, etc.

Furthermore, if the liquid sealing material has a large area in contact with a gas such as a cover gas, it may be oxidized by oxygen contained as an impurity in the cover gas, and solid or granular oxides may be generated on the surface.

The present invention was made with the aim of improving this point, and is designed to prevent liquid sealing material from entering the reactor vessel even if the pressure inside the reactor vessel abnormally decreases and the liquid sealant overflows from the freeze seal tub. A seal for a nuclear reactor plug that allows the overflowing liquid sealant to be easily collected into a sealing tank, and that does not increase the contact surface area between the sealant and the cover gas under normal usage conditions. It provides structure.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Reference numeral 1 in the figure is a furnace vessel, and its outer periphery is covered with a shielding structure such as concrete. Furnace vessel 1
A reactor core part 2 in which a large number of fuel assemblies are arranged is provided inside the reactor core part 2, and a fuel storage part 3 is provided around this reactor core part 2.

The reactor core 2 is connected to an inlet pipe 4 that introduces a coolant such as sodium. (However, depending on the type of reactor, the coolant may enter the reactor core once through the lower plenum.) The sodium introduced via the inlet pipe 4 is heated in the reactor core 2, and the coolant enters the reactor core once through the lower plenum. flows out from. The upper part of the furnace vessel 1 is open, and a fixing plug 6 is airtightly fixed to this opening. The fixed plug 6 is connected to the fuel storage section 3.
A fuel inlet/outlet machine 7 is provided vertically above the fuel tank. The fixing plug 6 is attached to the center of the furnace vessel 1.
An opening 8 having a center at a position O ₂ -O ₂ eccentric from O ₁ -O ₂ is formed. A rotary plug 9 is attached to the opening 8 so as to be rotatably inserted into the fixed plug 6. This rotary plug 9 is provided with a control rod drive device 10 that is located directly above the reactor core 2 when the rotary plug 9 rotates. A refueling machine 11, which is moved over the area directly above the fuel tank 3, is attached. A rotation bearing 12 is mounted between the rotating plug 9 and the fixed plug 6, and the rotary plug 9 is rotationally driven by a rotation drive device (not shown).

Note that 13 indicates a backup sticker.

Thus, a seal portion 14 is formed between the fixed plug 6 and the rotating plug 9. This seal portion 14 will be explained in detail with reference to FIG. 2. Note that FIG. 2 is a partial cross-sectional view showing only the right half of the seal portion 14 in an enlarged manner. That is, an annular seal bucket 15 is formed on the inner peripheral surface of the opening 8 in the fixed plug 6 over the entire circumference. In this seal tub 15, a low melting point metal such as Bi-Sn is housed as a liquid sealing material 16. On the other hand, a short cylindrical partition plate 17 is provided on the outer peripheral surface of the rotary plug 9 over the entire circumference. This partition plate 17
The tip of the liquid sealing material 1 in the seal tub 15 is
It is immersed in 6.

Therefore, the inside of the seal tub 15 and the rotary plug 9 are separated by the partition plate 17 into a first seal chamber 18a connected to the cover gas in the furnace vessel 1, and a second seal chamber 18a located on the bearing and seal 12, 13 side. Seal chamber 1
It came to be divided into 8b and 8b.

Then, a seal bucket 1 is placed in the first seal chamber 18a.
An annular overflow prevention tub 19 is provided with a bottom surface 19a extending from the upper end surface inside the tub.

Further, a baffle plate 20 is provided on the rotary plug 9 concentrically with the partition plate 17 so as to partition the center part of the upper end surface of the tub 19.

An opening 21a is formed in the lower part of the overflow prevention tub 19, and a recovery pipe 21 is connected to this opening 21a.
5 is connected to the lower part 15a of 5.

The valve 22 is located on the outside of the fixed plug 6 and allows manual operation and prevents overflow from the overflow trough 19.
This serves as an on-off valve when returning the liquid sodium accumulated in the tank to the seal tub 16.

Further, the tubs 15, 19, the pipe 21, and the valve 22 are heated by a heating device (not shown) so that the liquid sealing material 16 inside can be melted.

Next, the effects of the present invention related to the above structure will be explained.

If the gas pressure in the first seal chamber 18a in the reactor vessel 1 drops abnormally beyond the normal control range and the liquid seal material 16 is melted, the seal material 6 in the tub 15 will melt. It overflows from the tub 15 under the pressure of the second seal chamber 18b on the outside of the furnace. However, since the overflow prevention tub 19 is provided, the liquid sealing material 16 accumulates in this tub 19 and does not overflow, so that it does not fall into the reactor vessel. Furthermore, if the pressure inside the tub 15 suddenly decreases, or if outside air or gas stagnant in the second seal chamber 18b passes through the sealing material 16 of the tub 15 in the form of bubbles, the liquid sealing material 16 may overflow. If the flow rate increases, there is a risk that the liquid sealing material will jump over the tub 19 (carry over).

However, since the jama plate 20 is provided,
It can collide with this, fall into the tub 19, and stay there to prevent it from carrying over into the reactor vessel. After the abnormal pressure inside the reactor subsides, the liquid sealing material accumulated in the tub 19 is transferred to the sealing tub 1.
Return to within 5. In this case, valve 2, which is normally closed,
By opening 2, the sealing material will be released under its own weight into the recovery pipe 2.
1 and can be returned to the sealing tub 16.
The bottom surface of the overflow prevention tub 19 is higher than the liquid level of the sealing material 16 in the tub 15 in a normal state and is formed as an inclined surface, so that the sealing material can be easily collected into the tub 16. Furthermore, when the pressure fluctuation is within the normal control range, the liquid seal material remains inside the freeze seal tub 15 and the contact area with the cover gas does not change, so the degree of oxidation will not increase unnecessarily. do not have.

As explained above, according to the present invention, in the hermetic seal structure between the fixed plug and the rotating plug of the reactor vessel, an overflow prevention bucket is further connected above the seal bucket, and the overflow prevention bucket and the seal bucket can be recovered. Since it is connected through a pipe, it is possible to prevent the sealant that overflows from the seal bucket from getting mixed into the reactor coolant, which not only improves the safety of the reactor but also improves the liquid seal. Easier recovery of materials also has a significant effect on improving maintainability.

[Brief explanation of the drawing]

The drawings are for explaining one embodiment of the present invention, and FIG. 1 is a sectional view showing a schematic configuration of a fast breeder nuclear reactor, and FIG. 2 is an enlarged view of the main parts in FIG. 1. FIG. DESCRIPTION OF SYMBOLS 1...Reactor vessel, 2...Reactor core, 3...Fuel storage part, 6...Fixing plug, 7...Fuel loading/unloading machine, 8...
...Opening part, 9...Rotating plug, 10...Control rod drive device, 11...Fuel exchanger, 13...Backup seal, 14...Seal portion, 15...Freeze seal tub, 16...Liquid sealing material , 17... Partition plate, 18a, 18b... Seal chamber, 19... Overflow prevention tub, 20... Jam plate, 21... Collection pipe, 2
2... Valve.

Claims (1)

[Scope of Claims] 1. A pair of fixed plugs and rotating plugs that close an opening of a reactor vessel, and an annular sealing bucket that accommodates a liquid sealing material formed on either the fixed plug or the rotating plug. , a partition plate inserted into the sealing tub and provided on the lower surface of either of the plugs, and a partition plate connected to the sealing tub and having a bottom surface located above the upper end surface of the sealing tub. A plug for a nuclear reactor, comprising: an overflow prevention bucket; a recovery pipe that opens at the bottom of the overflow prevention bucket and communicates with the seal bucket; and a valve disposed in the recovery pipe. Seal structure. 2. The plug according to claim 1, further comprising a friction plate suspended from the lower surface of the plug, which is positioned below the upper end surface of the overflow prevention tub. Seal structure of nuclear reactor plug. 3. A sealing structure for a nuclear reactor plug as set forth in claim 1, wherein an inclined surface is formed on the bottom surface of the overflow prevention tub to facilitate the flow of sealing material into the sealing tub. .