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
2000-09-08
2003-09-23
Carone, Michael J. (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...
C250S506100, C250S515100, C250S518100
Reexamination Certificate
active
06625247
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a compact or lightweight cask and a production method of the cask, and to an embedded form. The cask is used for accommodating and storing spent fuel assemblies after combustion.
BACKGROUND OF THE INVENTION
A nuclear fuel assembly that has combusted to the final phase of the nuclear fuel cycle can not be used more and it is called used nuclear fuel. Such used nuclear fuel contains highly radioactive materials such as FP and thus needs to be cooled thermally. The used nuclear fuel is cooled in a cooling pit in the nuclear power plant for a predetermined period of time (three to six months). After that, the used nuclear fuel is accommodated in a cask which is a shielding vessel, and transported to a reprocessing plant e.g. by a truck and then stored. In accommodating used nuclear fuel assemblies in a cask, a holding element having a grid-like sectional shape referred to as a basket is used. The used nuclear fuel assemblies in question are inserted into cells which are a plurality of spaces formed in the basket in question, whereby an appropriate holding power against vibrations and the like is ensured during transportation. In the following discussion, a cask which forms a basis for developing the present invention will be described. The cask in question, however, is explained for the sake of convenience and does not fall into so-called well-known and well-used arts.
FIG. 17
is a perspective view showing one example of a cask.
FIG. 18
is a radial section view of the cask shown in FIG.
17
. The cask
500
comprises a cylindrical barrel body
501
, a resin
502
which is a neutron shielding member disposed on the outer periphery of the barrel body
501
, an outer casing
503
thereof, a bottom portion
504
and a lid portion
505
. The barrel body
501
and the bottom portion
504
are casts of carbon steel which is a gamma ray shielding material. Further, the lid portion
505
consists of a primary lid
506
and a secondary lid
507
. The barrel body
501
and the bottom portion
504
are connected by butt welding. The primary lid
506
and the secondary lid
507
are fixed with respect to the barrel body
501
via bolts of stainless and the like. Between the lid portion
505
and the barrel body
501
is disposed a metal O ring which keeps the interior air-tight.
Between the barrel body
501
and the outer casing
503
is provided a plurality of inner fins
508
for enabling heat conduction. The inner fins
508
are formed of copper so as to improve the heat conductivity. The resin
502
is injected into the spaces formed by these inner fins
508
in a fluid state, and then solidified by thermosetting reaction and the like. A basket
509
has a structure such that
69
square pipes
510
are assembled in a bundle as shown in
FIG. 17
, and is inserted into a cavity
511
of the barrel body
501
. A basket
509
has a structure that
69
square pipes
510
are assembled in a bundle as shown in
FIG. 17
, and is inserted into a cavity
511
of the barrel body
501
.
Reference numeral
515
designates a cell for accommodating a used nuclear fuel assembly. The relevant square pipe
510
is formed of an aluminum alloy mixed with a neutron absorbing material (boron: B) so that the inserted used nuclear fuel assembly will not go critical. On both sides of a cask body
512
are provided trunnions
513
(one of them is omitted) for suspending the cask
500
. Furthermore, on both ends of the cask body
512
are mounted buffer members
514
(one of them is omitted) to which lumber and the like is incorporated as a buffer material.
It is to be noted that it is desired that the above-described cask
500
is compact and lightweight from the view point of easy handling at the time of transportation and space saving at the time of storage. However, according to the configuration of the above-mentioned cask
500
, since the outermost square pipes
510
line contact with the inner surface of the cavity
511
to generate a space area S between the basket
509
and the cavity
511
, the diameter of the barrel body
501
becomes large and the cask
500
becomes heavy.
For addressing this problem, the only thing that is necessary to reduce the weight of the cask
500
is to make the thickness of the barrel body
501
small because the amount of radiation that leaks outside the cask is restricted by the total amount of neutrons and gamma rays. However, since the barrel body
501
is also a gamma ray shielding member, the barrel body
501
is required to have sufficient thickness to ensure the gamma ray shielding ability. Even in such a case, the thickness should fall within the range that is necessary and sufficient to shield the gamma rays. This is because excess thickness will avoid reduction of weight of the cask.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a cask which is compact and lightweight, a method for producing such cask, and an embedded form.
In order to solve the above problems, according to one aspect of this invention a cask comprises: a barrel body having an integrated forged structure and which shields gamma rays; a neutron shielding member provided outside said barrel body; and a basket having a cellular structure having an angular cross section, which cellular structure comprising cells each formed with a square shaped pipe which can shield neutrons; wherein a part or the whole of the outer shape of said barrel body is matched with a shape that is formed when the vertices of the angular cross section of said basket are connected, and wherein used fuel assemblies are accommodated and stored in said cells.
According to another aspect of this invention a cask comprises: a barrel body which shields gamma rays; a neutron shielding member provided outside said barrel body; and a basket having a cellular structure having plane sections and step-like sections, which cellular structure comprising cells each formed with a square shaped pipe which can shield neutrons; wherein a portion of the outer shape of said barrel body corresponding to the step-like sections of said basket is made of a shape such that it is parallel to a line that connects the vertices of the step-like sections of said basket, and wherein used fuel assemblies are accommodated and stored in said cells.
According to still another aspect of this invention a cask comprises: a barrel body which shields gamma rays; a neutron shielding member provided outside said barrel body; and a basket having a cellular structure having a angular cross section, which cellular structure comprising cells each formed with a square shaped pipe which can shield neutrons; wherein the internal shape of a cavity in said barrel body is matched with the outer shape of the angular cross section of said basket, said barrel body having an external shape having 8 or 12 corners, wherein some or all of the sides of said barrel body are made parallel to a line which connects the vertices of the angular cross section of said basket, and wherein used fuel assemblies are accommodated and stored in said cells.
In this cask, since the outside shape of the barrel body is matched to the outside shape of the basket, the portion having excess gamma ray shielding ability is removed, so that it is possible to reduce the weight of the barrel body. Moreover, by matching the shape of the neutron shielding member provided on the outer periphery of the barrel body to the outside shape of the barrel body, it is possible to make the cask compact.
In this connection, matching the outside shape of the barrel body to the outside shape of the basket means that the outside shape of the barrel body is appropriately formed within the range assumable by persons skilled in the art, for example, so as to have a shape corresponding to only large flat portion of the outside surface of the basket; so as to have a shape similar to that defined by connecting the apexes of the square pipes constituting the basket; or so as to have a shape strictly similar to the outside shape of the basket.
According to s
Najima Kenji
Ohkame Shinji
Ohsaki Masaru
Ohsono Katsunari
Matz David
Mitsubishi Heavy Industries Ltd.
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