Induced nuclear reactions: processes – systems – and elements – Handling of fission reactor component structure within... – Storage container systems for new and/or irradiated core...
Reexamination Certificate
2002-03-27
2004-08-17
Keith, Jack (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Handling of fission reactor component structure within...
Storage container systems for new and/or irradiated core...
C376S438000, C376S462000, C250S506100, C250S507100
Reexamination Certificate
active
06778625
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a square pipe, a basket and a spent fuel container which stores spent fuel aggregates.
BACKGROUND OF THE INVENTION
A nuclear fuel aggregate, which has been burnt and is no longer used in its terminal point of a nuclear fuel cycle, is referred to as a spent fuel aggregate. The spent fuel aggregate, which contains high radioactive substances such as FP, needs to be thermally cooled off so that it is cooled off for a predetermined period (for three to six months) in a cooling pit in a nuclear power plant. Thereafter, this is housed in a cask that is a shielding container, and transported by a truck or a ship to a recycling facility where it is stored. Upon housing the spent fuel aggregates in the cask, a holding frame having a lattice shape in its cross-section, called a basket, is used. The spent fuel aggregates are inserted into cells that are a plurality of housing spaces formed in the basket, one by one, thus, it is possible to ensure an appropriate holding strength against vibration, etc. during the transportation.
With respect to conventional examples of such a cask, various types thereof have been proposed in “Atomic eye” (issued on Apr. 1, 1998, Nikkan Kogyo Publishing Production) and Japanese Patent Application Laid-Open No. 62-242725. The following description will discuss a cask that forms a premise upon developing the present invention. However, the cask is shown for convenience of explanation, and is not necessarily related to the conventionally known and used device.
FIG. 23
is a perspective view that shows one example of a cask.
FIG. 24
is a cross-sectional view in the radial direction of the cask shown in
FIG. 23. A
cask
500
is constituted by a cylinder-shaped trunk main body
501
, a resin portion
502
placed on the outer circumference of the trunk main body
501
, an outer cylinder
503
, a bottom
504
and a lid section
505
. The trunk main body
501
and the bottom
504
are forged products of carbon steel that is a &ggr; ray-shielding substance. Moreover, the lid section
505
is constituted by a primary lid
506
and a secondary lid
507
made of stainless steel. The trunk main body
501
and the bottom
504
are joined to each other through butt welding.
The primary lid
506
and the secondary lid
507
are secured to the trunk main body
501
with stainless bolts. A hollow O-ring made of metal to which an aluminum coating, etc. is applied is interpolated between the lid section
505
and the trunk main body
501
so as to maintain the inside thereof in an air-tight state. Trunnions
513
which suspends the cask
500
are placed on both of the sides of a cask main body
512
(one of them is not shown). Moreover, buffer members
514
in which timber, etc. is sealed as a buffer member are attached to both of the ends of the cask main body
512
(one of them is not shown).
A plurality of inner fins
508
which allows heat conduction are placed between the trunk main body
501
and the outer cylinder
503
. The inner fins
508
are made of copper as their material in order to increase the efficiency of heat conductivity. Resin
502
is injected into a space formed by the inner fins
508
in a fluid state, and solidified and formed through a thermo-curing reaction, etc. A basket
509
has a construction formed by collecting
69
square pipes
510
into a bundle as shown in
FIG. 23
, and is inserted into a cavity
511
of the trunk main body
501
in a fixed state. The square pipe
510
is made of an aluminum alloy in which neutron-absorbingmember (boron, B) is mixed so as to prevent the inserted spent fuel aggregate from reaching the criticality. Moreover, each housing space formed by each square pipe
510
is referred to as a cell
515
, and each cell
515
can house one spent fuel aggregate. Trunnions
513
which suspends the cask
500
are placed on both of the sides of the cask main body
512
(one of them is not shown). Moreover, buffer members
514
in which timber, etc. is sealed as a buffer member are attached to both of the ends of the cask main body
512
(one of them is not shown).
A basket that has been used for a conventional radioactive substance storing container such as a cask and a canister is constituted by combining side faces of a plurality of square pipes with each other, therefore, in order to ensure a sufficient strength at the time of falling down, it is necessary to increase the plate thickness of the square pipe. For example, when a cask horizontally falls down, the load of the spent fuel aggregate is concentrated on the face end portions of each square pipe, thus, it is necessary to provide a thickness that can withstand this impact force. Moreover, since the basket needs to have a function to prevent the inserted spent fuel aggregate from reaching the criticality, the square pipe used for the basket is made of an aluminum alloy in which boron (B) is mixed as a neutron absorbing material. In order to provide this criticality preventive function, the square pipe for the basket needs to have a certain degree of thickness. For this reason, the outer shape dimension of the entire basket tends to become large, resulting in a greater mass in the entire basket.
Moreover, in order to protect the cask main body from an accident such as falling down during transportation of the cask, the buffer members
514
(one of which is omitted from the Figure) are attached to both of the ends of the cask (see FIG.
23
). The impact at the time of falling of the cask is buffered with the buffer members
514
being crushed. In this case, the margin of crushing in the radial direction, which is used for buffering the impact at the time of horizontal falling down, is ensured by increasing the diameter of the buffer members
514
, however, when land transportation is taken into consideration, the diameter of the buffer member
514
can not be increased unduly. When the outer diameter of the cask main body is reduced, the resulting space can be used as the margin of crushing in the buffer member
514
, thereby making it possible to reduce the outer diameter of the buffer member
514
.
SUMMARY OF THE INVENTION
It is an object of this invention to achieve at least one of the following points, to provide a basket which is constituted by pipes having a thickness thinner than conventional pipes and consequently to reduce the diameter of the spent nuclear fuel storing container, to provide a basket and square pipes used for storing spent fuel that are easily assembled with reduced off sets of the square pipes constituting the basket, and to provide square pipes used for storing spent fuel and a basket which can alleviate a stress concentration on a specific portion of the square pipe so as to reduce degradation in performances.
The spent fuel housing square pipe according to one aspect of the present invention comprises a plurality of square pipes assembled in a staggered arrangement. A spent fuel aggregate is housed inside the square pipes and in a space defined by walls of the square pipes. The corners of walls of each square pipe is formed into a terrace shape having a plurality of steps. When assembling the square pipes the steps of the terrace shape of adjacent square pipes are butted against each other.
These square pipes constitute a basket with a plurality of them being combined with each other in a staggered arrangement, therefore, in comparison with a basket constituted by allowing the side faces of square pipes to contact each other, it is possible to make the thickness of the side face of the square pipe thinner. This is because, if the plate thickness of the square pipe side face is equal to the size corresponding to two sheets of the conventional plate, the rigidity would virtually double the conventional rigidity. Therefore, if the plate thickness is equal to the size corresponding to two sheets of the conventional plate, it becomes possible to withstand a greater impact accordingly. Moreover, the corner portion is formed into a terrace shape, and the pipes are combined with each other b
Matsuoka Toshihiro
Ohsono Katsunari
Ookame Shinji
Keith Jack
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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