JPS60260890A - Shielding plug - 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 (Technical Field of the Invention) The present invention relates to an improvement in a shielding plug that is fitted into and closes an upper opening of a reactor vessel such as a fast breeder reactor.

[Technical background of the invention and its problems]

In general, the reactor vessel of a fast breeder reactor forms a reactor core in which nuclear fuel is loaded at its interior center, and this reactor core is immersed in a liquid metal primary coolant.

Therefore, particularly high reliability is required regarding the integrity of the reactor vessel.

However, in this type of reactor vessel, the temperature of the coolant at the core outlet of the reactor core is high, and the reactor vessel shell in contact with this core outlet coolant becomes high temperature, so the design of the reactor vessel requires strict high-temperature structural design conditions. It is demanding and extremely difficult.

The upper opening of such a furnace vessel is hermetically closed by a shielding plug fitted therein.

Conventionally, this type of shielding plug is formed into a cylindrical shape that conforms to the circular shape of the upper opening of the furnace vessel, and is adapted to fit air-tightly into the upper opening of the furnace vessel.

A heat shielding layer is formed at the bottom of the shielding plug, and a shielding body is disposed around the outer periphery of the heat shielding layer.

However, due to assembly limitations, a required gap, for example, a gap of at least about 5 mm, is formed in an annular shape between the heat shield layer and the shield body. Conventionally, the heat shield layer has a laminated plate structure, so the pressure loss is greater than that of the annular gap, and it was not thought that significant natural convection would occur in the annular gap. However, in an experimental device simulating such a conventional shielding plug, it was confirmed that natural convection occurs in the annular gap.

That is, as shown in the schematic diagram of FIG. 4, natural convection that rises and falls along the axial direction occurs in the annular gap C defined between the heat shield layer A and the shield 1)iB. therefore,
In a furnace vessel in which such a conventional shielding plug is fitted into the upper opening, uneven temperature distribution occurs in the circumferential direction, which is one of the causes of thermal stress and deformation in the furnace vessel. Ta.

Furthermore, due to cover gas convection in the annular gap C, activated coolant vapor was deposited in the annular gap C, and a region with a high radiation dose rate was locally emitted above the shielding plug.

In addition, if this annular gap C is narrowed in order to prevent natural convection between the annular ICs, when the heat shield layer A thermally expands, the heat shield layer A will extend in the outer radial direction and the shield body There was a risk that B would be pressed and stress would be generated. Of course, such stress does not harm the integrity of the reactor vessel, etc., but from the standpoint of taking thorough safety measures, it is desirable to suppress the generation of such stress.

[Purpose of the invention]

The present invention was made in consideration of the above-mentioned circumstances, and suppresses the occurrence of natural convection in the annular gap defined by the heat shielding layer and the shielding body, and the heat shielding layer expands the shielding body by thermal expansion. It is an object of the present invention to provide a shielding plug that reduces the stress of pressing in the direction.

[Summary of the invention]

In order to achieve the above-mentioned object, the shielding plug according to the present invention is constructed as follows.

In a shielding plug that is airtightly fitted into an opening of a reactor vessel to seal the opening, an annular gap is formed between a heat shielding layer and a shielding shell, and a corrugated stepped portion is quickly formed in this annular gap. A plurality of corrugated plates are interposed, the continuous direction of the corrugated step portions of these corrugated plates is aligned with the circumferential direction of the annular gap, and a required gap is set between adjacent corrugated plates in the circumferential direction. configured.

[Embodiments of the invention].

Hereinafter, one embodiment of the shielding plug according to the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1G is a vertical sectional view schematically showing a shielding plug according to an embodiment of the present invention, and reference numeral 1 in the figure is a reactor vessel of a liquid metal cooled nuclear reactor. A reactor core 2 to which nuclear fuel is loaded is formed within the reactor vessel 1, and a coolant 3 such as sodium, for example, is accommodated so as to submerge the reactor core 2. The upper opening of the furnace vessel 1 is hermetically sealed with a shielding plug 4 fitted airtightly. The shielding plug 4 can be of single, double or triple rotation type depending on the fuel exchange method, but since the present invention can be applied to any of these types, the single rotation type will be explained here.

The shielding plug 4 is fitted with a fixed plug 5 which is fitted into the upper opening of the furnace vessel 1 and then fixed to the furnace vessel 1, and the fixed plug 5 is eccentrically passed through the shell in the axial direction and is rotatably attached. It mainly consists of a rotating plug 6, and a core upper part 1111i1s6A is installed in the rotating plug 6. The in-furnace cover gas 7 is in the space formed between the squares under the fixed and rotating plugs 5 and 6, that is, between the lower end surfaces of the plugs 5 and 6 and the liquid level of the coolant 3. Filled. Therefore, during normal operation of the reactor, the temperature is considerable, for example about 500°C.
The heat retained in the coolant 3 heated back and forth is thermally conducted to the lower surfaces of both plugs 5 and 6 through this furnace cover gas 7. For this purpose, both the fixed and rotary plugs 5.6 are provided with shielding layers 8A, 8B at the upper part in the axial direction, and heat shielding layers 9A, 9B at the lower part, respectively, to shield heat and the like. The heat shielding layers 9A and 9B of both the fixed and rotating plugs 5 and 6 have a laminated temporary structure in which a plurality of thin plates 10A' and 10B are laminated at equal intervals in the axial direction, as shown in FIG. They are suspended from the heat shielding layers 8A, 8B, etc., respectively.

These heat shielding layers9. Among A and 9B, the heat shielding layer 9A of the fixed plug 5 has a shielding body 1 on both sides of its outer periphery and inner periphery.
1A' and 11B are respectively provided in an annular manner, and on the other hand, the heat shielding layer 9B of the rotary plug 6 has a shielding body 1 only on its outer periphery.
1C is installed around it. First and second annular gaps 1. ? A and 12B are set respectively.

Similarly, a third annular gap 12G is set between the outer periphery of the heat shielding layer 9B of the rotating plug 6 and the inner periphery of the shielding body 11C.

These first, second, and third annular gaps 12A.

12B, 12C have corrugated panels 13A, 13B,
13G are inserted respectively. Each of these corrugated panels 13A, 13B, and 130 is made of a corrugated plate that is bent to form a plurality of corrugated stepped portions 13a in the width direction, and is bent into an arc shape with a required curvature in the width direction.

That is, each corrugated panel 13A, 138, 130
are the first, second, and third annular gaps 12A, 12B, 1'
2C, respectively, and a plurality of corrugated panels 13A, 138.13G are arranged in a single layer in each annular gap 12A, 12B, 1'2G. In addition, each col, gate panel 13A
, 13B, 13C, the continuous direction of the corrugated step portion 13a is made to coincide with the circumferential direction of each heat shielding layer 9A, 9B, and the top of each corrugated step portion 13a is located between each annular space 1! Ji12A, 12B
, 12G, for example, as shown in FIG. 3, are pressed against the outer peripheral surface of the heat shielding layer 9A and the inner peripheral surface of the shield J]1i11A. That is, each corrugated panel 13A, 13B, 13C is sandwiched between the heat shielding layer 9A, 9B and the shielding body 11A, 11B, IIC.

As a result, the circumferential direction of each of the annular gaps 12A, 12B, and 12G is closed by a large number of corrugated steps 13a, and a large number of small spaces are defined, and gas convection in the circumferential direction is blocked. , natural convection in each annular gap 12A, 12B, 12C is suppressed. This can prevent uneven temperature distribution from occurring in the circumferential direction of the furnace vessel 1. In addition, the heat shielding layers 9A, 9B forming the respective annular gaps 12A, i2s, 12G and the respective shielding layers 1ji11A, 11B,
When thermal expansion etc. occurs in Ll and C and compressive force acts on each corrugate panel 13A, 13B, 13G,
Each of the corrugated panels 13A, 13B, and 13C deforms depending on the direction in which the compressive force is applied, and can absorb the compressive force.

Each corrugated panel 13A, 138, 130 is a corrugated panel 13A adjacent to each other in the circumferential direction in each annular gap 12A, 12B, 12C.

A required mounting interval 14 is set between 13B and 130, respectively. Therefore, each corrugated panel 13A,
When the corrugated step portions 13a of 13B and 13C receive compressive force in the direction of their protruding height, each of the corrugated panels 13A
', 13B, , 13G width direction end is above installation interval 1
4 and can absorb the compressive force.

Furthermore, as a result of suppressing the natural convection of the in-furnace cover gas 7 in each of the annular gaps 12A, 12B, and 12C, the activated coolant vapor is deposited to transfer to each of the annular gaps 12A, 12B, and 12G due to this cover gas convection. is suppressed.

In addition, each corrugated panel 13A, 13B, 13C is divided into a large number of elements in a direction perpendicular to its width direction, in other words, in the axial direction, to facilitate insertion into each annular gap 12A, 128, 120. It may be configured as desired.

〔Effect of the invention〕

As explained above, the present invention provides a shielding plug that is airtightly fitted into an opening of a reactor vessel and seals the opening, in which an annular gap is formed between a heat shielding layer and a shield shell, and the annular gap is A plurality of corrugated plates having corrugated stepped portions are interposed therebetween, and the continuous direction of the corrugated stepped portions of these corrugated plates is aligned with the circumferential direction of the annular gap, and the required distance between adjacent corrugated plates in the circumferential direction is made. It was configured by setting the gap between. Therefore, according to the present invention, each annular gap formed between the heat shielding layer and the shielding body in both the fixed and rotating shielding plugs is closed in the circumferential direction by each corrugated panel, thereby defining a large number of small spaces. Therefore, natural convection in each annular gap can be suppressed. This suppresses uneven temperature distribution, thermal stress, and thermal deformation in the circumferential direction of the furnace vessel and shielding plug caused by natural convection in each annular gap, reduces stress caused by thermal expansion of the thermal shielding layer, and improves reliability. A shielding plug with high properties can be obtained.

In addition, as a result of suppressing natural convection in the annular gap, the amount of activated coolant vapor that migrates to the annular gap due to cover gas convection is suppressed, and the radiation dose rate on the top surface of the shielding plug can be reduced. It is also effective.

[Brief explanation of drawings]

1 to 3 each show an embodiment of the shielding plug according to the present invention, FIG. 1 is a vertical sectional view schematically showing the shielding plug of the embodiment, and FIG. 2 is a heat shielding of the fixed plug. FIG. 3 is an enlarged vertical cross-sectional view of the main part showing the outer periphery of the layer, and FIG. FIG. 4 is a schematic diagram for explaining the occurrence of natural convection in each annular gap. 1... Reactor vessel, 2... Core, 3... Coolant, 4...
... Shielding plug, 5... Fixed plug, 6... Rotating plug, 7... Furnace cover gas, 8A, 8B... Shielding layer, 9A. 9B... Heat shielding layer, IIA, IIB, 11C... Shielding body, 12A... First annular gap, 12B... Second annular gap, 12G... Third annular gap, 13A, 13B,
13C... Corrugated panel, 14... Installation interval. Applicant's agent Kuzuru Hatano l Figure 2 Figure 4

Claims (1)

[Claims] 1. In a shielding plug that is airtightly fitted into an opening of a reactor vessel to seal the opening, an annular gap is formed between the heat shielding layer and the shielding shell, and the annular gap is A plurality of corrugated plates having interconnected corrugated stepped portions are interposed, and the continuous direction of the corrugated stepped portions of these corrugated plates is aligned with the circumferential direction of the annular gap, and the adjacent corrugated plates are mutually arranged in the circumferential direction. A shielding plug characterized in that a required gap is set between the shielding plugs. 2. The heat shielding layer portion has a gas layer of cover gas formed in the gap of a laminated plate structure in which plate materials are laminated.
Shielding plugs as described in Section. 3. The shielding plug according to claim 1, wherein the reactor vessel is of a liquid metal cooled type.