JPS61176891A - Cask for storage functioning as transport in combination of radiation sheild - 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 One means currently used to dispose of spent nuclear fuel assemblies is to store them in large metal containers or casks. Such casks are usually handled as cargo many times (loaded and unloaded onto freight cars, transported to storage areas, placed in storage rooms, etc.), so if they are dropped in an accident, they cannot be transported. It must be strong enough to withstand this without damaging the container or the fuel assembly contained within. Also, a means must be provided to dissipate the decay heat generated from the spent fuel assembly. Otherwise, the spent fuel assembly would be damaged by this decay heat and the container would be filled with harmful gases. In addition, 1 gamma ray and neutron radiation issues must be handled safely and with long term %IC.

SUMMARY OF THE INVENTION According to the present invention, a single thick-walled alloy container is provided that allows spent fuel assemblies to be safely stored for long periods of time. The container has a double lid construction with a pair of metal O-ring seals and a welded seal to prevent leakage from the cask in the unlikely event of an accident. The interior of the cask is designed to better hold the fuel assembly in place and aid in heat dissipation.

Preferred Embodiment In FIG. 1, numeral 10 designates a container or cask in which spent nuclear fuel assemblies can be stored. The cask is a cylindrical carbon steel vessel approximately 18 inches (18 centimeters) in diameter and 16 inches (41 centimeters) high.

The cylindrical wall is 10.5 inches (27 centimeters) thick with a bottom thickness of 9 inches (23 centimeters) and a top lid thickness of 8.5 inches (22 centimeters). This steel thickness provides the necessary gamma and neutron shielding, eliminating the need for separate hydrogen liquid and hard neutron shields. Both conventional and enhanced nuclear reactor fuel assemblies can be safely and reliably stored in Casque 0.

Within the cask 10 is a monolithic or integral steel lattice structure. The lattice structure consists of plates 12 (FIGS. 1 and 2) welded together to form open-ended boxes 14 in which the spent fuel assemblies are placed. Box 1 like this
There are 24 4's. Plate 12 is 178 inches (3 mm) thick.
to 1/4 inch (6 mm), extending from a point proximate the bottom of the cask to a point proximate the top of the cask. Within the integral cruciform member, this lattice structure conducts the generated decay heat and radiates it to the walls of the cask where it is dissipated into the air surrounding the cask. The lattice structure also provides the necessary support to protect a fuel assembly in the event of an accident, such as when the cask is dropped from a crane, hoist, or truck.

The cross-shaped member is made of carbon steel and is initially assembled into the cask by sliding down from a point on the bottom of the cask close to the top of the cask (Figure 2). The arms are tightly fitted within the channel and when the cask reaches thermal equilibrium (typically 300-400°C), the arms firmly engage the channel and engage the cylindrical wall of the cask. K to ensure good thermal contact. This provides good heat transfer from the fuel assembly to the cylindrical wall of the cask, allowing for efficient heat dissipation.

Four ears 32 are provided at the upper end of the cask, and two ears 34 are provided at the lower end, thereby facilitating handling of the cask. Usually, a crane (not shown) is used to pick up or unload the cask from a truck or storage area, and wires are hooked onto these ears. 36 and outer lid 38 are installed.

The inner cover 36 is finch thick (18 cm) and has 40 bolts.
When installed in the correct position, it becomes a primary strength barrier. Preferably, a large number of bolts 4o, such as 30 or 40, are used.

The outer cover 38 is designed to prevent the bolts 40 from being exposed to the atmosphere during long-term storage, and to maintain a tight seal even in the event of an accident where the inner cover loosens, such as when a bolt breaks in an accident. The purpose is to provide a sense of redundancy. A hollow metal O-ring 42 is compressed to form a seal when the inner lid 36 is attached to the plug 40. In addition to this seal, an annular seal ring 44 is placed over the bolt 40 and seal welds 46.4g are formed along all of the inner and outer edges to form a second seal. Tighten the outer cover 38 with bolts 50 and remove the second hollow metal gQ.
Compressing ring 52 creates a third effective seal.

As is clear from the gt diagram and FIG. 2, one gas passage 54 is provided in the cylindrical wall of the cask. These gas passages are used to introduce inert gas into the cask to prevent oxidation inside the cask. These gas passages are closed with plugs when the cask is placed in fuel assembly storage.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of the fuel storage cask, FIG. 2 is a sectional view taken along line 2-2 in FIG. 1, and FIG. 3 is a partially enlarged sectional view showing the sealing structure of the lid of the cask. 10...Cask, 12...Board, 14...Box, 1
6.1g, 20.22 -- Arm, 24, 26, 28゜3
0...Groove member, 32, 34...Ear piece, 36...Inner cover, 3
8φ・Outer cover, 40・・Bolt, 42 fist @ 0 ring, 44
...Seal ring, 46.48.9 Sealing welded part, 50.
・Bolt, 52...O-ring, F/to, / FIG, 2 FIG, 3

Claims (1)

[Claims] an external steel cylindrical wall, an integral steel bottom, a removable steel lid, means for sealingly attaching the steel lid, and a cross-shaped member dividing the interior of the cask into four quadrants; a plurality of vertically disposed metal open end boxes attached to the cruciform member and to each other in each quadrant;
are supported within the cask by guide rails adjacent the outer edges of each of the four arms, each of these four guide rails providing relative heat transfer between them but with good thermal conductivity. sufficient contact has been made to carry out the
Transport and storage of a radiation shield for the storage of spent fuel assemblies, characterized in that the heat generated by the fuel assemblies can be easily dissipated through the cylindrical wall. Cask for.