Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
1999-11-15
2001-12-25
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
C376S261000, C376S446000
Reexamination Certificate
active
06333957
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to nuclear fuel bundles of a type having water rods serving as supports between a lower tie plate and an upper tie plate and particularly relates to a tool kit for fabricating, inspecting and handling the nuclear fuel bundle.
In a recent nuclear fuel bundle design by the assignee of the present invention, mechanical support for the fuel bundle in an unchanneled condition is provided by a pair of central water rods connected to the lower tie plate rather than by conventional tie rods. The water rods are typically threaded and screwed into the lower tie plate and tie bars are fixed at the upper ends of the water rods for attachment to a lifting tool. The upper ends of the tie bars terminate in heads having one or more flats designed for proper orientation and fit into similarly machined complementary openings in the lift tool. The tie bar heads have a D-flat configuration, although other non-circular cross-sectional configurations can be utilized. Preferably, at least one flat is used.
BRIEF SUMMARY OF THE INVENTION
In this new fuel bundle, the two water rods lie in close proximity to one another in the fuel bundle. As a consequence, their relative lengths from the face of the lower tie plate to the underside of the tie rod ends are required to meet tight tolerances. For example, the length tolerance for the pair of water rods in a particular bundle preferably lies within 0.020 inches of one another to prevent undesirable tilting of the bundle during vertical handling or transport. The water rod assemblies are adjustable in length. This is accomplished by providing for relative axial movement of the water rod and the tie bar which, when adjusted, provide a water rod assembly of fixed predetermined length. To adjust the length, however, it is necessary to first rotate the water rod assembly to engage the threaded lower end plug of the water rod into the lower tie plate and then thread the tie bar into the water rod. The adjustment is further complicated by the requirement for at least one tabbed water rod assembly. That is, at least one water rod assembly requires a plurality of generally radially projecting tabs at axially spaced positions therealong for engagement with the spacers of the fuel bundle whereby the tabs prevent the spacers from disengaging from the water rod assemblies and sliding up or down the assemblies. These tabs lie only on one side of the water rod assembly and must lie in a predetermined orientation in final assembly. This requirement enables adjustment of the water rod in only one turn increments. Thus, the first adjustment to the overall length of the water rod assembly can be accomplished by a rotation of the water rod within a single rotation so that the water rod is one turn or less from bottoming out on the lower tie plate. The secondary adjustment of the tie bar is also restricted to a minimum of a single rotation because in final position, the D-flat on the upper end of the tie bar must be in a designated fixed rotational orientation. Additionally, the threads at the end plugs of the water rods and the lower ends of the tie bars are of different pitch. Consequently, by mutual adjustment of the water rod and tie bar, the tabbed water rod length can be set within a specified range, for example, 0.040 inches.
More particularly, the adjustment of the orientation of the tie rod and water rod relative to one another involves first rotating a threaded washer at the junction of the tie rod and water rod and moving a lower axially tabbed lock washer from locking relation with an end plug at the upper end of the water rod. Thus, by releasing the threaded washer and rotating it upwardly along the tie bar, the tie bar can be screwed farther into the upper water rod end plug by rotating it at least one full turn or multiples thereof before the lower lock washer is reseated in the water rod upper end plug and the threaded washer is tightened against it. Likewise, if the tie rod is to be rotated out of the upper water rod end plug to lengthen the water rod assembly, the threaded washer is threaded down on the tie bar. To accomplish this, the threaded washer must first be raised to permit the lower lock washer's axial tab to disengage from the upper water rod end plug.
The adjustment in the lengths of the water rod assemblies requires with respect to the tabbed water rod setting the length within a predetermined range, i.e., ±0.040 inches, and within one turn of bottoming out on the lower tie plate. It is also necessary to properly orient the water rod tabs and the tie bar D-flats. With respect to setting the length of the untabbed water rod, it is necessary to adjust its length within the predetermined tolerance, i.e., ±0.040 inches and also to set its length within a predetermined tolerance, e.g., ±0.020 inches of the tabbed water rod assembly length. It is also necessary to properly orient the tie bar D-flat. Special tools and gauges are therefore necessary to accomplish these actions and in accordance with a preferred embodiment of the present invention are provided as part of a tool kit. The tools and gauges of the tool kit include a socket, a flat orientator wrench, a threaded washer wrench, orientator gauges, orientator cap and a tie bar simulator. The first five tools and gauges are used in setting and maintaining the lengths and orientation of the water rods. The last device, i.e., the tie bar simulator is used in checking the alignment of the D-flat holes in the lift bars and lift tools.
The tools and gauges of the tool kit overcome significant problems in fabricating and handling the new fuel bundle design. For example, problems associated with locking and unlocking the threaded washer especially in a bundle with some of the fuel rods installed, rotation of the tie bars to adjust their lengths and orientation of the water rod tabs and the tie bar D-flats in a bundle where some or all of the fuel rods installed are overcome by the present invention. Additionally, the tool kit provides tools and gauges for checking the alignment of the two tie bar D-flat ends over maximum, minimum and nominal dimensions, maintaining the relative orientation of the tie rod D-flats during handling and shipping and checking the orientation of the machined D-flat holes in the lift bars and tools prior to shipment.
In a preferred embodiment according to the present invention, there is provided a tool kit for adjusting the length of a water rod assembly in a nuclear fuel bundle having a lower end plug for threaded engagement in a lower tie plate, the water rod assembly including a pair of water rods, a pair of tie bars having flats at upper ends thereof and releasable locking subassemblies for respectively securing the tie bars and water rods to one another, forming joints therebetween, comprising first and second gauges each having a gauge body with first and second openings generally complementary in shape to the respective upper ends of the tie bars having the flats, the openings having parallel axes, margins of each gauge body defining the openings being offset from one another in the direction of the axes, the openings of the second gauge being reduced relative to the openings in the first gauge body whereby the angular orientation of the water rods about their respective axes is adjustable upon application of the first and second gauges to the tie rods.
In a further preferred embodiment of the present invention, there is provided a tool kit for adjusting the length of a water rod assembly in a nuclear fuel bundle having a lower end plug for threaded engagement in a lower tie plate, the water rod assembly including a pair of water rods, a pair of tie bars having flats at upper ends thereof and releasable locking subassemblies for respectively securing the tie bars and water rods to one another forming joints therebetween. The tool kit comprises a pair of wrenches having wrench heads including openings respectively complementary in shape to the flats at the upper ends of the tie bars and ref
Apple, Jr. Edward G.
Peters William C.
Smith David G.
Carone Michael J.
General Electric Company
Nixon & Vanderhye
Richardson John
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