JP3132983B2 - Cavity seal for reactor vessel and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure inside a containment vessel, and more particularly to a structure of a cavity seal for a reactor vessel.

[0002]

2. Description of the Related Art Conventionally, in a light water-cooled reactor, as shown in FIG. 4, a reactor vessel 1 is a concrete structure 3 (including a steel frame and the like inside) in a containment vessel (not shown).
Is installed so as to hang down in the reactor cavity 5 formed in the above. The reactor cavity 5 is filled with shield water during refueling, and nuclear fuel in the reactor vessel 1 is transferred through the shield water. Therefore, the cavity seal 7 is used so that shielding water does not enter the well or the hole in which the reactor vessel 1 is contained. The cavity seal 7
One application is sufficient if it is provided only at the time of refueling, but it is often fixed (it is always provided) due to problems such as complicated installation and removal and radioactive contamination.

FIG. 5 shows a conventional cavity seal 7 described above.
Is shown as an enlarged sectional view. Although the size of the reactor vessel 1 varies depending on its output, it generally has a diameter of several meters. Therefore, the cavity seal 7 attached to the outer peripheral portion of the flange of the reactor vessel body 1a
It is a considerably large annular structure, and the connecting ring 7
a, 7b and a cylindrical seal plate 7c.
The connecting rings 7a and 7b function as connecting members for the vessel main body 1a and the reactor cavity 5, respectively. The seal plate 7c is formed by assembling a large number of plate members by welding as shown in FIG. The reactor vessel main body 1a is surrounded by a heat insulating material 8, and the cooling air 9 flows as shown by an arrow.

[0004]

The concrete structure 3 exposed to the outside air or the cooling air is kept at a relatively low temperature during the operation of the reactor, whereas the concrete structure 3 is kept at a relatively low temperature. The upper part reaches a considerably high temperature during operation, and the amount of thermal expansion also increases. Therefore, a relative displacement occurs between the two. This relative displacement is absorbed by the deformation of the cavity seal 7 between them. These situations will be described with reference to FIG. 7. FIG. 7A shows a state in which the reactor operation is suspended (including the time of manufacture), and when the reactor is operated, the state shown in FIG. Become. That is, the deformation concentrates on the joint between the joint ring 7b that tends to expand together with the flange of the reactor vessel main body 1a and the seal plate 7c that behaves the same as the joint ring 7a restrained by the concrete structure 3. High stress is likely to occur in the part. This is because the reactor vessel 1 also becomes larger in accordance with the tendency of the reactor power to increase. Further, when the size of the seal plate 7c is increased, the number of used plate materials increases, and the number of welding lines also increases.
Anyway, since the welded portion is a portion where material defects are relatively likely to occur as compared with other portions, stochastically, if thermal deformation is concentrated here, thermal fatigue fracture is likely to occur. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reactor vessel cavity seal in which the number of welding lines is small and thermal deformation is not concentrated on a weld portion, and a method of manufacturing the same.

[0005]

According to the present invention, there is provided, in accordance with the present invention, a bottom surface of a reactor cavity formed by a concrete structure, and a reactor vessel suspended and supported in a hole in the bottom surface. The cavity seal that closes the gap is formed by welding a lower disk part joined to the bottom surface of the reactor cavity, an intermediate cylindrical part, and an upper ring part joined to the reactor vessel, and A bay-shaped cross section projecting inward in the radial direction is formed at the lower end of the section. According to the method of the present invention, the cylindrical portion of the cavity seal is formed by bending a strip material into a cylindrical shape, and welding and joining both ends of the strip material to form a cylindrical blank. A bellows structure extending in the circumferential direction is formed by roll forming in an appropriate place, and then manufactured through a process of cutting the outer end of the bellows structure in a circumferential shape, and this is formed into a lower disk portion and an upper ring portion. Each is welded to finally produce a cavity seal.

[0006]

In the cavity seal having the above-described structure, during operation of the reactor, the lower disk portion is fixed to and driven by the bottom surface of the reactor cavity, and the upper ring portion is fixed to and driven by the reactor vessel. However, the difference in thermal expansion between the two is absorbed by the deformation of the cylindrical portion. Since the cylindrical portion has a bay-shaped cross-section at its lower end, it deforms like a curved beam when viewed in cross section, and the deformation is dispersed and does not concentrate on the joint. Further, in the manufacture of the above-mentioned cylindrical portion, the axial welding line exists only between both ends of the rounded strip, and the number of welding lines is reduced.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, the same reference numerals are given to the same parts including the drawings for explaining the conventional structure. In FIG. 1, a main body 1a of a reactor vessel 1 is surrounded by a heat insulating material 8, and an upper ring portion 21 of a cavity seal 20 according to the present invention is joined to an upper flange thereof by welding. Also, a lower disk portion 25 connected to the upper ring portion 21 via the cylindrical portion 23
Are welded to a liner plate 15 provided on the surface of the concrete structure 3. The cavity seal 20 is
After the attachment, it is covered and protected by the protective lid 16.

FIG. 2 shows details of the structure of the cavity seal 20. The upper ring portion 21 joined to the container body 1a has a relatively thick but thin extension portion 21.
a, and the extended portion 21 a is joined to the upper end of the cylindrical portion 23 by welding. In addition, the cross-section changing part of the base of the extension part 21a draws an arc of an appropriate diameter to reduce stress concentration. Further, a lower portion of the cylindrical portion 23 is formed with a bay-shaped cross-sectional portion 23a having a gentle inflection portion, and the lower disk portion 25 is welded thereto. Further, the lower disk portion 25
It has an engaging ring 25a similar to the conventional one, and is fixed to the liner plate 15 by welding. The aforementioned welding is
Regardless of the location, the continuous welding is performed without any gap, so that even if the refueling shielding water is supplied to the outside of the cavity seal 20, it does not leak to the inside of the reactor vessel 1 side.

Next, a procedure for manufacturing the cylindrical portion 23 having the above-described shape will be described with reference to FIG. 3. A band plate material having a predetermined width and length is bent by a bender or the like and formed into a cylindrical shape. The parts are butt-welded to form a cylindrical blank 30 (a). Then, a predetermined position of the cylindrical blank 30 is formed by the rolls 17 and 19 to form the bellows structure 31 (b). Further, if the outer end of the bellows structure 31 is cut in a circumferential shape and the outer end and the lower part of the blank 30 are removed, the remaining upper part of the blank 30 becomes the above-mentioned cylindrical portion 23, and the bellows structure 31 The remaining portion becomes the bay portion 23a (c). The cylindrical portion 23 thus manufactured is welded to the upper ring portion 21 and the lower disk portion 25 by a usual method.

The plate-shaped portion of the lower disk portion 25 other than the connecting ring 25a is generally manufactured by welding and joining an arc-shaped plate material with a welding line extending in a radial direction. The upper ring portion 21 and the connecting ring 25a may be manufactured from an integral material, or a plurality of segment portions may be assembled by welding.

The cavity seal 20 manufactured as described above and installed between the reactor vessel 1 and the bottom surface of the reactor cavity 5 has shielding water applied to the reactor cavity 5 as in the conventional case. Sometimes prevent its outflow. When there is a relative displacement between the reactor cavity 5 and the reactor vessel 1 due to a difference in thermal expansion, the upper ring portion 21 is relatively displaced to the left (in the drawing) in FIG. Due to the action of 23a, it is gently deformed to absorb the difference in thermal expansion. Further, since there is no welded portion in the suddenly changing section of the upper ring portion 21, thermal stress is not concentrated there.

[0012]

As described above, according to the first aspect of the present invention, since the bay-shaped cross-section is formed in the cylindrical portion of the cavity seal, the deformation due to the difference in thermal expansion occurs not concentrated but occurs in a dispersed manner. Thermal stress is small, and thermal fatigue fracture can be prevented. According to the invention of claim 2, when manufacturing the cylindrical portion, since the strip material is bent and welded at both ends,
The weld line is minimized and thermal fatigue fracture of the weld can be prevented.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a main part of an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of FIG.

FIG. 3 is a process chart showing the procedure of the method of the present invention.

FIG. 4 is a conceptual diagram showing a situation in which the cavity seal of the present invention is used.

FIG. 5 is a partial cross-sectional view showing a state where a conventional device is attached.

FIG. 6 is a perspective view showing a part of a conventional device.

FIG. 7 is an explanatory diagram showing a state of a defect of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor vessel 3 Concrete structure 5 Reactor cavity 20 Cavity seal 21 Upper ring part 23 Cylindrical part 23a Bay-like cross section 25 Lower disc part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-214886 (JP, A) JP-A-59-70997 (JP, A) Jikai Sho 54-3600 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) G21C 13/028

Claims (2)

(57) [Claims] 1. A cavity seal for closing between a bottom surface of a reactor cavity formed by a concrete structure and a reactor vessel suspended and supported in a hole in the bottom surface, the cavity seal being joined to the bottom surface of the reactor cavity. A lower disk portion, an intermediate cylindrical portion, and an upper ring portion joined to the reactor vessel are welded to each other, and are formed in a bay shape projecting radially inward at a lower end portion of the cylindrical portion. A cavity seal for a nuclear reactor vessel, wherein a cross section is formed. 2. A bellows which is formed by bending a strip material into a cylindrical shape, welding and joining both ends of the strip material to form a cylindrical blank, and circumferentially extending by roll forming at an appropriate position of the cylindrical blank. A structure is formed, and thereafter, an outer end portion of the bellows structure is circumferentially cut to form a cylindrical portion, and a lower disk portion and an upper ring portion are welded to the cylindrical portion, respectively. Item 3. A method for producing a cavity seal for a nuclear reactor vessel according to Item 1.