Induced nuclear reactions: processes – systems – and elements – Handling of fission reactor component structure within... – Fuel component
Reexamination Certificate
1999-05-07
2001-11-20
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Handling of fission reactor component structure within...
Fuel component
C376S268000
Reexamination Certificate
active
06320922
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tool for extracting both full-length and partial-length fuel rods from and inserting such rods into nuclear fuel assemblies and to methods of extracting and inserting the fuel rods relative to the assemblies.
BACKGROUND OF THE INVENTION
Nuclear fuel bundle assemblies in boiling water nuclear reactors typically include a plurality of fuel rods extending in generally parallel relation one to the other from a lower tie plate. A plurality of fuel rod spacers are spaced one from another along the length of the fuel bundle assembly to maintain the lateral spacing of the fuel rods relative to one another. In addition to full-length fuel rods, fuel bundles often include part-length fuel rods which extend upwardly from the lower tie plate through a fewer number of the spacers than do the full-length fuel rods and which part-length fuel rods terminate below the upper ends of the full-length fuel rods. Additionally, one or more water rods typically upstand from the lower tie plate.
In certain fuel bundle assemblies, mechanical support for the fuel bundle is provided by a threaded connection between a pair of central water rods and the lower tie plate. Thus, the lower ends of the full-length and part-length fuel rods terminate in end plugs receivable in and axially removable from openings in the lower tie plate. Additionally, the upper ends of the full-length and part-length fuel rods have similar type end plug terminating in barbed end caps. These upper end caps facilitate removal of one or more of the fuel rods from the nuclear fuel assembly.
It will be appreciated that the fuel rods, both full-length and part-length, are not readily accessible since they are internal to the fuel bundle assemblies and do not extend up to the top of the water rod tie bar. Moreover, the full-length rods are held in place by spacers, typically about eight or nine spacers, and require a substantial force, for example, as much as 70 pounds, to axially withdraw each fuel rod from the fuel bundle assembly. The part-length rods are held by a lesser number of spacers, e.g., three spacers, and do not require as much axial force for their removal. However, the part-length rods are snapped into the lower tie plate with specially designed lower end plugs which require additional axial force for removal.
In order to withdraw a fuel rod from the fuel bundle assembly, an extractor must be able to be inserted and removed from the fuel bundle without damaging any of the assembly components including the fuel rod upper end caps, the fuel rods per se and the spacers and must pass through the assembly of fuel rods in the assembly, as well as ancillary fuel bundle structure. Further, the extractor tool must have the capacity to engage the barbed end cap of the upper end plug so that it can be used to not only withdraw the fuel rod but to reinsert a fuel rod and to reseat a partial or full-length fuel rod lower end plug into the lower tie plate. Finally, the extractor tool must be able to releasably lock onto the fuel rod's upper end plug's barbed cap so that the fuel rod can be withdrawn from the lower tie plate and the fuel assembly with the necessary pulling force, e.g., as much as 60 to 70 pounds.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided an extractor tool which can be easily and quickly inserted into and removed from a nuclear fuel bundle assembly and which tool is engageable with the upper end plugs of both full-length and part-length fuel rods in a manner to releasably lock about the end plugs to enable the fuel rods to be withdrawn and reinserted into the fuel bundle assembly. To accomplish the foregoing, the extractor tool of a preferred embodiment of the present invention includes an inner rod typically pivotally mounting split sections of a collet at a fuel rod engaging end thereof, an outer tube disposed about and coaxial with the inner rod and a drive element cooperable between the inner rod and outer tube for axially displacing the inner rod and outer tube relative to one another without relative rotation thereof such that the collet sections are cammed between open and closed positions. Particularly, the collet sections preferably comprise generally semi-cylindrical sections having flanged ends for engaging below a barbed end of the fuel rod end plug. The collet sections are pivotally mounted to the end of the inner rod and are cammed by relative axial displacement of the outer tube and inner rod between the open and closed collet positions.
The extractor tool also includes a drive element threaded onto the inner rod. The drive element is rotatable relative to the outer tube and axially advances or retracts the outer tube relative to the inner rod upon threading the drive element and inner rod in opposite directions, respectively. A pin prevents rotation of the outer tube and inner rod relative to one another thereby preventing rotation of the outer tube relative to the spacers and fuel rods upon insertion of the extractor tool into the fuel bundle to engage and withdraw a fuel rod. Additionally, a slide hammer is provided on the inner rod for impacting an anvil surface on the inner rod when the inner rod engages the end plug to jar loose the engaged fuel rod should it be stuck in position engaged in the fuel bundle.
To use the extractor tool hereof, the drive element is threaded on the inner rod to advance the outer tube relative to the inner rod to close the collet sections. When closed, the extractor tool is inserted into the fuel bundle assembly and preferably engages the closed collet with the top face of the end plug of the fuel rod to be withdrawn. The tool may then be backed off the end plug and the drive element rotated to withdraw the outer tube relative to the inner rod camming the collet sections into the open position. By then axially advancing the extractor tool, the open collet jaws straddle the barbed end of the end plug at the same time the end face of the inner rod engages the end face of the end plug locating the tool axially relative to the end plug. The drive element is threaded in the opposite direction to advance the outer tube relative to the inner rod to close the collet jaws about the end cap. When closed, the extractor tool can be axially withdrawn to remove the fuel rod from the fuel bundle assembly. Should the fuel rod lie stuck in the bundle assembly, the slide hammer can be impacted against the inner rod anvil to jar loose the fuel rod.
The tool can also be used to insert full-length and part-length fuel rods into the fuel assembly. The foregoing described procedure for extraction can be reversed for fuel rod insertion.
In a preferred embodiment according to the present invention, there is provided a tool for displacing fuel rods in nuclear fuel bundle assemblies, comprising an elongated inner rod, an elongated outer tube coaxial about and axially movable relative to the inner rod, a collet carried by the inner rod including collet sections each having a distal end for engaging an end plug of a fuel rod, the collet sections being movable between collet-open and collet-closed positions in response to relative axial movement of the inner rod and the outer tube, a threaded portion carried by the inner rod and a drive element threaded to the threaded portion and coupled to the outer tube for axially displacing the outer tube and the rod relative to one another in response to threading the drive element and the threaded portion relative to one another to move the collet sections between the open and closed positions.
In a further preferred embodiment according to the present invention, there is provided a method of extracting elongated fuel rods having end plugs terminating in end caps from a nuclear fuel assembly employing an extractor tool having an inner rod, an outer tube coaxially about and axially movable relative to the inner rod and a collet at an end of the tool having end cap engaging sections movable between an open position spaced from the
Apple, Jr. Edward G.
Peters William C.
Smith David G.
Carone Michael J.
General Electric Company
Mun Kevin
Nixon & Vanderhye
LandOfFree
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