JPS5811039B2 - Shielding plug for fast reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shielding plug for a fast reactor that uses liquid metal as a coolant, and particularly to a shielding plug that has a good heat insulating effect as a rotating plug.

A fast breeder reactor (hereinafter referred to as a fast reactor) using liquid metal as a coolant generally has a structure schematically shown in FIG.

That is, the fast reactor 1 includes a reactor vessel 6 having an inlet pipe 4 and an outlet pipe 5 for a coolant such as liquid sodium 3 to cool the housed reactor core 2, a thick flange 7 provided at the open end of the reactor vessel 6, and a reactor vessel 6 having an inlet pipe 4 and an outlet pipe 5 for cooling a reactor core 2 housed therein, a thick-walled flange 7 provided at the open end of the reactor vessel 6, and a reactor vessel 6 having an inlet pipe 4 and an outlet pipe 5 for a coolant such as liquid sodium 3 to cool the contained reactor core 2. It consists of a rotary plug 9 equipped with a furnace upper mechanism 8 for controlling and driving the furnace.

A gap 11 is provided between the rotary plug 9 and the flange 7 to facilitate rotation of the rotary plug 9 during fuel exchange.
A gas seal 12 and a rotary plug bearing 13 are provided.

Here, the liquid sodium 3 that has flowed into the reactor vessel 6 from the inlet pipe 4 is heated as it flows through the reactor core 2 and is heated through the outlet pipe 4.
flows out from

The flange 7 is placed on and fixed to a pedestal part 14 made of concrete.

The rotary plug 9 is provided to rotate the reactor upper mechanism 8, as well as to block out neutrons and gamma rays and provide heat insulation.

Therefore, a cylindrical body 15 is provided on the lower surface of the rotary plug 9, and a laminated portion 16 of stainless steel plates, a graphite block 17, and a gas cooling layer 18 are suspended within the cylindrical body 15, and the laminated portion 16 insulates the heat transmitted to the upper part. Also, together with the graphite block 17, it also shields neutrons and gamma rays.

Note that the heat that cannot be sufficiently insulated by the laminated main portion 16 and the like is forcibly cooled by the gas flowing through the gas cooling layer 18, and the upper surface of the rotary plug 9 is maintained at an operationally acceptable temperature.

Furthermore, as shown in FIG. 2, an example is known in which the laminated portion 16 is directly provided on the lower surface of the rotary plug 9 that has a protrusion 18 formed on the lower surface, but in this example, the metal cylindrical body 15 is removed. As a result, as shown in FIG. 1, the heat flow flowing through the cylindrical body 15 is reduced and the blocking effect becomes effective.

However, in either case, insulation is performed using a metal laminate plate made of stainless steel or the like, resulting in a shielding plug that is costly in terms of material costs, manufacturing costs, and assembly costs.

Further, since the heat resistance of the shielding plug is not sufficient, there is a drawback that the shielding plug becomes thicker, resulting in higher cost.

The purpose of the present invention was to eliminate the above-mentioned drawbacks, and it is an object of the present invention to provide a thin fast reactor shielding plug that is inexpensive and has excellent heat insulation performance.

That is, the present invention selects a packed bed of rock such as basalt which is inexpensive and has heat insulating properties as the heat insulating material, and maintains the packed bed in a vacuum to create a barrier plug with a higher performance heat insulating part. be.

Hereinafter, one embodiment of the fast reactor shield plug according to the present invention will be described with reference to FIG.

In FIG. 3, the same parts as in FIG. 1 are indicated by the same reference numerals, and the explanation of the overlapping parts will be omitted.

In FIG. 3, the cylindrical portion 15 of the shielding plug 9 has a cylindrical shape with a bottom.
A packed layer 16 of rock such as basalt, a graphite block 17, and a gas forced cooling layer 19 are housed in the chamber. Furthermore, it is maintained under high vacuum conditions using a high vacuum pump (such as an ion pump) 24.

During operation, the pipe 27 is connected to the vacuum pump side pipe 26 through the vacuum flange 20, but when replacing fuel, the valve 21 is closed and the flange 20 is removed to rotate the rotary plug.

Further, a vacuum pump for depressurization is usually used by closing the valve 23 and opening the valve 22 when starting to evacuation.

After evacuating to a vacuum level of about 1O-3torr, valve 2
2, close the valve 23, and switch to the high vacuum pump 24 to create an even higher vacuum (about 10-5 torr).

Once a high vacuum state is achieved, the valve 21 may be closed and the vacuum pumps 25 and 24 may be stopped.

The thermal conductivity ke of a packed bed of ordinary particles can be expressed by a curve as shown in FIG. 4, where kf is the thermal conductivity of the gas and ks is the thermal conductivity of the material of the particles.

That is, the thermal conductivity ks of the constituent substances is the thermal conductivity k of the gas
Even if a material that is considerably larger than f is selected, the thermal conductivity will not increase that much if it is used as a filling material.

In other words, the packed layer made of material with ks/kf=103 also has ks/kf=103.
The thermal conductivity of the packed bed with kf=106 is almost the same unless the thermal conductivity of the fluid is different.

Therefore, conversely, if the thermal conductivity of the gas can be made small, ke can be made small since the value of ke/kf hardly changes even if the value of ks/kf becomes large.

Here, the thermal conductivity of a gas exhibits a nearly constant value when the distance d between conductive objects is sufficiently larger than the mean free path l of the gas (a>>l), but on the other hand, when l>>d In some cases, it becomes proportional to the pressure.

Therefore, if the pressure can be maintained at a high vacuum such that l>>d, the thermal conductivity of the gas can be reduced, and the thermal conductivity of the packed bed can be reduced.

In addition, if a filling material with a particle size of about 10-1 cm is selected, 1
At 0-2 to 1O-1 torr, l≒d, so 1O
If the pressure is about -5 torr, the thermal conductivity of the gas is d, ignoring radiation heat transfer, and the pressure condition for l≒d is d.
The smaller the particle size, the higher the pressure, so the finer the particle size, the better the insulation performance even if the degree of vacuum is low.

Furthermore, the smaller the particle size, the better, since the finer the particles, the smaller the radial heat transfer.

As explained above, according to the present invention, the packed layer of basalt, etc., maintained in a high vacuum state is housed in the lower cylindrical body of the shayahei plug, so the insulation effect is excellent, and the thinness of the shayahei plug is improved. This makes it possible to reduce the overall cost.

Note that in the above embodiments, it is not necessary to evacuate the entire filled layer to a vacuum, and for example, a structure in which only the upper layer can be evacuated may be used.

Further, the vacuum pump or the like may be placed on the shielding plug.

Furthermore, the filler may be made of a material other than rock as long as it is heat-resistant and inexpensive.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view schematically showing a conventional fast reactor, FIG. 2 is a longitudinal sectional view schematically showing a shielding plug in a conventional fast reactor, and FIG. 3 is a longitudinal sectional view schematically showing a shielding plug for a fast reactor according to the present invention. Fig. 4 is a vertical cross-sectional view showing a partial systematic view of the state in which the Hei Plug is installed in a nuclear reactor. It is a curve diagram showing the relationship between thermal conductivity of gas. 1... Fast reactor, 2... Core, 3... Coolant, 4...
...Inlet piping, 5...Outlet piping, 6...Furnace vessel, 7
... Flange, 8 ... Furnace upper mechanism, 9 ... Rotating plug, 15 ... Cylindrical body, 16 ... Laminated part, 17 ...
・Graphite block, 18...gas cooling layer.

Claims (1)

[Claims] 1. A rotating plug rotatably fitted with a gap in the opening of the furnace vessel, a cylindrical body protruding from the lower surface of the rotating plug, and a cylindrical body filled under reduced pressure. A fast reactor plug is characterized by having a particle layer made of a heat-resistant material such as a rock such as basalt or a metal particle layer.