Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
2003-01-02
2004-11-09
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
Reexamination Certificate
active
06816563
ABSTRACT:
BACKGROUND OF THE INVENTION AND PRIOR ART
The present invention concerns a spacer and a fuel assembly for a nuclear reactor, preferably for a nuclear light water reactor. The spacer is designed such that it forms a plurality of cells for holding parallel elongated elements which extend through the cells or for allowing these elements to pass through the cells. Each of said cells is defined by a plurality of side portions which together surrounds one of said elongated elements when such an element is arranged such that it extends through the spacer. The spacer is designed to be arranged in a nuclear reactor such that said cells, and thereby said elongated elements, extend in essentially a first direction in which a cooling medium is intended to flow. Each cell thus comprises a first end which is intended to be positioned upstream with regard to said first direction and a second end which is intended to be positioned downstream with regard to said first direction. For at least one of said cells it is the case that at least one of said side portions which define the cell comprises at least one flow-influencing member which is formed by a part of said side portion and which is folded out from the side portion. Said side portion from which said flow-influencing member is folded out comprises a first and a second edge surface which are connected to each other, which edge surfaces have different principal directions of extension which correspond to the directions of a first and a second edge of said flow-influencing member in a non folded out state of the flow-influencing member.
A spacer of this kind is known from U.S. Pat. No. 5,112,571. The purpose with said flow-influencing member is to influence the flow of the cooling medium which flows through the spacer in order to improve the cooling of the parallel elongated elements which consist of fuel rods. The above mentioned flow-influencing member will below also be called fin. The mentioned U.S. patent document shows that the cells have a plurality of fins which are folded out from the side portions of the cells. The document shows one embodiment where a cut which extends in the vertical direction has been done from the upper edge of the cell. A part of the cell has thereby been folded out. The side portion from which the fin has been folded out thus comprises only one edge surface which extends essentially vertically. The document also shows a second embodiment where the fin is positioned further down in the cell. The side portion thereby comprises an upper edge surface which extends essentially horizontally and a second edge surface which starts from the upper edge surface and extends essentially vertically. The folded out fins thus have an essentially triangular shape.
U.S. Pat. No. 5,440,599 shows folded out fins which are arranged on top of the spacer itself, i.e. above the cells themselves which hold the elongated elements in position.
SE-C2-510 816 shows spacers where fins have been folded out from the spacer cell after that one or two vertical cuts have been made from the upper edge from the spacer cell.
The Swedish patent application 9803177-6, which has been made public, shows spacers with cells of an open construction where fins of essentially triangular shape are arranged.
It should be noted that it exist nuclear reactors of different kinds, for example so-called boiling water reactors and so-called pressure water reactors. In such nuclear reactors nuclear fuel is usually arranged in fuel rods. A plurality of such fuel rods are usually arranged parallel to each other in a fuel assembly. In order to hold the fuel rods at determined distances from each other, a fuel assembly comprises a plurality of spacers.
FIGS. 1
,
2
and
3
show different kinds of known spacers. Such spacers comprise a plurality of cells
10
through which the fuel rods are intended to extend. The cells
10
are arranged parallel to each other. Usually the cells
10
, and thus the fuel rods, extend in the vertical direction. The spacer, and each cell
10
in the spacer, thus has a first end
16
which is located at the bottom and a second end
18
which is located at the top. A cooling medium, usually water, is intended to flow upwards through the fuel assembly. A main flow direction which thus is parallel to the extension of the fuel rods and the cells
10
is marked with
14
in FIG.
1
.
FIG. 1
shows a kind of spacer with sleeve-shaped cells
10
. In the shown case, the cells
10
are cornered in order to hold the fuel rods in position with a spring force. The spacer of the kind that is shown in
FIG. 1
will below be called a spacer with sleeve-shaped cells
10
. Such a kind of spacer may also have cells
10
of essentially circular shape. The sleeve-shaped cells
10
are preferably welded together in order to form a spacer.
FIG. 2
shows a kind of spacer where the cells
10
are formed as relatively open elements with support points and resilient members which are arranged to hold the fuel rods in position. This kind of spacer will below be called a cell-spacer. Between the cells
10
in those kinds of spacers which are shown in FIG.
1
and in
FIG. 2
a number of flow channels
32
are formed through which a cooling medium may flow.
In
FIG. 3
another kind of spacer is shown which below will be called an egg-crate spacer. Such a spacer comprises a plurality of cells
10
of essentially square shape. Since the cells
10
have a squared shape, no further flow channels
32
of the kind which have been described above are formed in this kind of spacer. However, spaces are of course formed between the fuel rods
19
also in the kind of spacer which is shown in
FIG. 3
, in which spaces a cooling medium may flow.
In order to achieve a good cooling of the fuel rods is important that the cooling medium is conducted to the fuel rods in an efficient manner. The above described documents show different kinds of fins which are designed to conduct a cooling medium towards the fuel rods.
SUMMARY OF THE INVENTION
A purpose of the present invention is to achieve a spacer which in a more efficient manner contributes to directing a cooling medium towards the fuel rods. A further purpose is to achieve such a spacer with a relatively simple construction. Still another purpose is that the flow-influencing members which form part of the spacer shall have a relatively large flow directing surface without the necessity to make these flow-influencing members very large.
These purposes are achieved by a spacer of the kind which is described initially above and which is characterised in that said first edge surface extends from said second end of the cell and has an extension in at least said first direction and in that said second edge surface extends from that end of said first edge surface that is positioned upstream and has an extension in at least a direction which is perpendicular to said first direction.
Spacers according to the present invention thus have the advantage that the flow-influencing member, i.e. the fin, may be fabricated relatively simply since it forms a folded out part of the cell. Since the second edge surface, which is located upstream, has an extension perpendicularly to the flow direction, the folded out fin gets a relatively large flow directing area. It has in flow experiments appeared that the fin which forms part of the spacer according to the present invention contributes to an essentially improved cooling of the fuel rods.
According to a second aspect of the invention, the above mentioned purposes are achieved also by a spacer of the kind which is described initially above and which is characterised in that said first edge surface extends from said first end of the cell and has an extension in at least said first direction and in that said second edge surface extends from that end of said first edge surface that is positioned downstream and has an extension in at least a direction that is perpendicular to said first direction. According to this aspect of the invention, the same advantages are achieved as with the above described spa
Behrend Harvey E.
Swidler Berlin Shereff Freidman, LLP
Westinghouse Atom AB
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