Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
1999-03-10
2001-08-21
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
C376S439000, C376S442000, C376S462000
Reexamination Certificate
active
06278758
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a nuclear reactor fuel assembly, and more specifically to a support grid structure for supporting fuel rods thereof.
BACKGROUND OF THE INVENTION
A typical structure of a fuel assembly for a pressurized water reactor is shown in FIG.
5
. Describing it briefly, an upper and lower nozzle
1
,
3
having a plurality of coolant flow holes machined therein are connected with a plurality of hollow guide tubes
5
which are parallel to one another. Support grids
7
having grid cells positioned in a rectangular arrangement which individually receive the hollow guide tubes
5
therethrough and which are fixed to the guide tubes
5
support the fuel rods
9
by placing them individually through the remainder of the grid cells. A fuel assembly
10
is thus constructed and in order to more clearly show the structure, a portion of the fuel assembly
10
from which the surroundings about one support grid
7
are removed is shown in a partial perspective view in FIG.
6
. As readily understandable from
FIG. 6
, the disposition of the fuel rods
9
is in a square arrangement with equal numbers of columns and rows and it is constructed showing some of the fuel rods
9
at specified locations being replaced with the hollow guide tubes
5
.
The support grid
7
defining grid cells which individually receive, as described before, the fuel rods
9
and the hollow guide tubes
5
disposed in a square arrangement, is essentially constructed by combining two kinds of thin metal straps as shown in
FIGS. 7
a
and
7
b
, namely, straps
20
,
30
, with each other in a perpendicular relationship. The support grid
7
defines grid cells located in a 14×14 arrangement, and the straps
20
,
30
each essentially have an identical configuration and differ from each other in the positions at which slits
21
,
31
for receiving another strap corresponding thereto are formed. In other words, slits
21
in the strap
20
are positioned on an upper side (downstream in the coolant flow), while slits
31
in the strap
30
are positioned on a lower side (upstream in the coolant flow). Mixing vanes
23
,
25
,
33
,
35
are integrally formed at a downstream edge of the straps
20
,
30
in alignment with the slits
21
,
31
. Furthermore, tabs
27
,
29
,
37
,
39
for welding the straps
20
,
30
which are assembled by using slits
21
,
31
are provided. The positional relationship among the slits
21
,
31
, the mixing vanes
23
,
25
,
33
,
35
and the tabs
27
,
29
,
37
,
39
that are described above is schematically shown in an enlarged manner in
FIGS. 5
a
and
8
b.
The above described mixing vanes
23
,
25
and
33
,
35
are bent and slanted in opposite directions, respectively, as shown in
FIG. 9
, when the straps
20
,
30
are assembled. A partial top view of the support grid
7
corresponding to
FIG. 9
is shown in FIG.
10
. As seen from
FIG. 10
, the outer extremities of the mixing vanes
23
,
25
,
33
,
35
are close to the fuel rods
9
depicted by dash-and-two-dot lines, but not close enough to come into contact with the fuel rods
9
. In these structures, since a coolant stream which flows through the support grid
7
impinges on the mixing vanes
23
,
25
,
33
,
55
, the coolant stream is agitated to be stirred and make the temperature distribution therein uniform.
SUMMARY OF THE INVENTION
However, in the conventional support grid
7
, as clearly shown in
FIGS. 8 and 10
in particular, welding apertures
26
,
36
are formed by an inner side of the mixing vanes
23
,
25
,
33
,
35
, respectively. Since the coolant stream passes through these welding apertures
26
,
36
without impingement or interference, no agitation of the coolant passing through the welding apertures can be expected and the agitating and mixing function of all the mixing vanes is therefore not sufficient to achieve the desired effects.
Accordingly, an object of the present invention is to provide a support grid with mixing vanes for a fuel assembly which do not increase a pressure drop in the coolant flow and which further provides improved agitating and mixing functions.
In order to accomplish the object described above, according to the present invention, in a support grid of a nuclear reactor fuel assembly wherein the support grid has a plurality of first straps which are made of thin metal band plate, and a plurality of second straps which are made of thin metal band plate, the first and second straps are each provided with slits extending widthwise for receiving the other of the straps and assembled so as to receive opposite straps in the slits of each strap to cross each other and thereby form an eggcrate structure, mixing vanes integrally formed on a side edge of the first and second straps adjacent to a crossed area and in alignment with a slit, each of the mixing vanes being slanted so as to be adjacent to a nuclear reactor fuel rod to be placed through a grid cell of the eggcrate structure, the slanted portion of the mixing vane being shaped so as to maximize an area of the slanted portion of the mixing vane projected onto a plane perpendicular to coolant flow direction. Preferably, the mixing vanes are shaped such that they have a welding aperture formed in a base portion at the side of the slit, and a bend line extending parallel to a longitudinal axis of the strap is located closer to a distal end side than the welding aperture and a curved outer edge of the mixing vanes is located at the distal end side of the bend line. Furthermore, in place of the above, the shape of the mixing vane can be formed such that the bend line at which the slanted surface of the mixing vane begins is slanted with respect to the longitudinal axis of the strap so as to avoid the welding aperture and the length of the mixing vane of the first strap is larger than the length of the mixing vane of the second strap.
REFERENCES:
patent: 3920515 (1975-11-01), Ferrari et al.
patent: 4039379 (1977-08-01), Patterson et al.
patent: 4268356 (1981-05-01), Kmonk et al.
patent: 4389369 (1983-06-01), Bryan
patent: 4803043 (1989-02-01), DeMario et al.
patent: 4827063 (1989-05-01), Bokers et al.
patent: 4879090 (1989-11-01), Perrotti et al.
patent: 5061437 (1991-10-01), Whitt
patent: 5110539 (1992-05-01), Perrotti et al.
patent: 5139736 (1992-08-01), Bryan
patent: 5180548 (1993-01-01), Verdier
patent: 5183629 (1993-02-01), Canat et al.
patent: 5188797 (1993-02-01), Bryan
patent: 5265140 (1993-11-01), Perrotti
patent: 5307393 (1994-04-01), Hatfield
patent: 5371769 (1994-12-01), Kato et al.
patent: 5402457 (1995-03-01), Suchy et al.
patent: 5440599 (1995-08-01), Rodack et al.
patent: 5859887 (1999-01-01), Richards
patent: 6144716 (2000-11-01), Nguyen et al.
patent: 0304724 (1989-03-01), None
patent: 0 332 941 (1989-09-01), None
patent: WO9408341 (1994-04-01), None
Imaizumi Masahiko
Suemura Takayuki
Gottlieb Rackman & Reisman P.C.
Jordan Charles T.
Keith Jack
Mitsubishi Heavy Industries Ltd.
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