Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
1997-04-23
2001-05-01
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
C376S440000, C376S446000
Reexamination Certificate
active
06226343
ABSTRACT:
TECHNICAL FIELD
The invention relates to an water rod in a fuel assembly of a boiling water nuclear reactor and, more particularly, to a water rod that is directly attachable to the upper and lower tie plates of the fuel assembly without an end plug.
BACKGROUND
A fuel assembly in a nuclear reactor includes a matrix of parallel rods containing fissionable fuel and/or water coolant flow. These parallel rods are held at a fixed spacing by spacer meshes located intermittently along the length of the fuel assembly. The matrix of fuel rods is supported at their lower ends by a lower tie plate, which also guides the fuel rod end plugs laterally. The lower tie plate also includes flow holes to provide an inlet for coolant flow into the fuel assembly. Similarly, the top end of the rod matrix is covered by an upper tie plate that restrains the fuel rod upper end plugs laterally and provides flow holes for the exit of coolant from the fuel assembly. One or more of the water and/or fuel rods is used as a structural member that is attached to both the lower and upper tie plates and serves the purpose of carrying a structural load of the assembly and maintaining a fixed distance between the lower and upper tie plates.
Prior designs using the water rod as the structural member typically have complex assemblies including members to transition from a large to a smaller diameter and/or end fittings to attach to the lower and upper tie plates as illustrated in FIG.
1
. Even when the water rod is not used as the structural member, the assembly is complex as shown in
FIG. 2
with many of the same components.
In particular, referring to
FIG. 1
, a conventional water rod has a central cylindrical tube
10
secured between an upper tie plate
12
and a lower tie plate
14
. The central tube
10
has a plurality of inlet flow holes
16
that allow water to be driven through the rod, thus introducing moderating material within the fuel rod matrix. An upper reducer
18
and a lower reducer
20
are welded to upper and lower end of the central tube
10
respectively. The reducers
18
,
20
effectively reduce the diameter of the central tube
10
to accommodate end fittings. An upper end fitting
22
and a lower end fitting
24
are welded to the upper and lower reducer
18
,
20
, respectively and are configured to be secured to the upper and lower tie plate, respectively.
Referring to
FIG. 2
, when the water rod is not intended to be the structural member for the fuel assembly, even more intricate end fittings are coupled to the central tube for connection to the upper and lower tie plates.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the invention to provide a water rod for a fuel assembly of a boiling water nuclear reactor that is simple in construction, inexpensive to manufacture, and that has reduced inspection requirements. It is another object of the invention to provide a water rod that is directly attachable to a tie plate of the fuel assembly without an end plug.
These and other objects and advantages of the invention are achieved by providing a water rod for a fuel assembly of a boiling water nuclear reactor that includes a first end and a second end, wherein at least one of the first and second ends is directly attachable to a tie plate of the fuel assembly without an end plug. The at least one of the first and second ends may include threads adapted to be received by a threaded aperture in the tie plate. Moreover, the at least one end may be swaged such that it comprises a narrower diameter than a remainder of the water rod. The end may be flared such that it has a diameter that is greater than a diameter of a tie plate aperture and/or keyed to prevent rotation of the water rod, or the end may be provided with one of a male and female portion of a bayonet fitting adapted to be received by the other of the male and female portion of the bayonet fitting in the tie plate.
An end insert may be disposed within the water rod at the at least one end, wherein the end insert may be provided with a plurality of flow apertures therethrough. An end cap that is attachable over the end may also be provided, and similar to the end insert, the end cap may be provided with a plurality of flow apertures therethrough.
In accordance with another aspect of the invention, there is provided a fuel assembly for a boiling water nuclear reactor that includes an upper tie plate; a lower tie plate; and a water rod having first and second ends and being supported between the upper and lower tie plates, wherein at least one of the first and second ends is directly attachable to a respective one of the upper and lower tie plates without an end plug.
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Frederickson Christian D.
King Harold B.
Behrend Harvey E.
General Electric Company
Nixon & Vanderhye P.C.
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