JPH0138557Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a shock absorber for casks (spent nuclear fuel transport containers) used in nuclear power plants, which fall due to an unexpected accident while storing spent nuclear fuel in a fuel pool. The purpose is to absorb the shock caused by accidents and prevent secondary accidents from occurring.

A cask is a container that stores spent nuclear fuel and transports it to a reprocessing plant, and its size is, for example, 1.8 m in diameter, 6 m in height, and approximately 80 tons in weight.
Horizontally transporting the cask within the power plant is carried out by lifting it slightly with a crane and crawling along the ground. Furthermore, when placing the fuel on the bottom of the fuel pool or taking it out from the pool, it must be suspended or lifted within a predetermined vertical distance. At this time, a shock absorber is installed on the bottom of the fuel pool, which can receive the falling cask body without any hindrance in case of an unexpected accident such as a breakage of the suspension wire. However, since the conventional shock absorber has a cylindrical outer shape with a downward convexity, a three-dimensional press mold is required for press working, making it very expensive. Additionally, the cask body may come into contact with a locking edge protruding inward from the top of the cylinder, which poses a safety problem.
The present invention has been made in view of these points.

Examples will be described with reference to the drawings.

The rectangular cylinder 1 has a two-dimensionally curved plate with a wide upper side on each side, each of which is welded to a lower depression, and a sealed bottom plate 2 is welded to the lower side. A plurality of cylindrical stoppers 3 are fixed to the upper surface of the bottom plate 2. The coil spring 4 is fitted into each stopper at its lower end and is at the same height. The square plate 5 is supported horizontally on the coil spring 4, and is movable up and down within the square cylinder above the stopper. The locking edges 1a are fixed to the four corners of the upper side of the rectangular cylinder, and can lock the rectangular plate 5 pushed up by the coil spring 4.

The present invention is constructed as described above, and is fixed to the bottom of the pool below the suspension line of the cask C.
When the cask C suspended from the crane is gently lowered onto the square plate 5 as shown in the figure, the spring 4 is compressed to the height of the stopper 3, and the cask is seated on the stopper 3 without any trouble. In addition, if the wire breaks and the cask falls, in addition to the compression resistance of the coil spring, the water in the rectangular cylinder also provides a strong buffering effect. In other words, as the rectangular plate tries to descend rapidly, the water under the rectangular plate tries to escape upward through the gap on the outer periphery of the rectangular plate, but as the rectangular plate descends, this gap narrows, causing a strong orifice phenomenon. This is because it shows resistance. The combination of both effects makes it possible for the cask to sit on the stopper in this case as well without applying an excessive impact load.

Conventional structures that have the same purpose as the present invention include:
There is a cylindrical type with a concave bottom as shown in Figure 3. However, in the conventional structure, when the cask C is seated on the upper disk, it may deviate from the suspension line and come into contact with the locking edge protruding inward of the cylinder, and if the cask C falls due to an unexpected accident. The upper disk was made larger to provide more room. Moreover, a considerable amount of space is required to position the cylindrical body in the corner of the fuel pool. In addition, the cylindrical shape of the bottom opening can only be processed using a press mold with a three-dimensional curve, which requires large-scale equipment. Other known examples include a telescope type multi-stage piston structure (not shown) and a structure in which the cask is dropped into a cylinder in the form of a piston, but in the former case, the piston does not move due to dirt getting into the sliding surface. In the latter case, the cask body collided with or got caught on the inner wall of the cylinder and was damaged, posing a safety problem. In contrast, the present invention has a simple structure and rectangular cylindrical shape, so
Its production involves rolling each side into a two-dimensional curved surface.
It is only necessary to weld each part, making it inexpensive.

It can be placed along the corner of the fuel pool, making effective use of pool space. Also,
Since the locking edges 1a are provided at the four corners of the square, the cask body does not come into contact with the locking edges 1a.

The above are the features of the present invention.

[Brief explanation of the drawing]

Figure 1 is a front view of the present invention, Figure 2 is a plan view of the same,
FIG. 3 is a plan view of the conventional structure. 1... Square tube, 1a... Locking edge, 2... Bottom plate,
3...Stopper, 4...Coil spring, 5...Square plate, C...Cask.

Claims (1)

[Scope of utility model registration request] In a cask shock absorber installed at the bottom of a fuel pool, four plates of the same shape with a two-dimensional curved surface with a wide upper side are welded to each have a rectangular cross section, and a rectangular cylinder with a concave bottom is welded to the bottom side of the cask. , a plurality of cylindrical stoppers fixed onto the bottom plate, and a coil spring of equal height whose lower end is fitted into each stopper,
A buffer consisting of a rectangular plate supported by the upper end of the coil spring and movable up and down above the stopper within the rectangular cylinder, and locking edges fixed to the four corners of the upper side of the rectangular cylinder and capable of locking the rectangular plate pushed up by the coil spring. Device.