Spacer capture mechanism for non-round water rods

Abstract: A nuclear reactor fuel bundle assembly having a plurality of fuel rods and a non-round water rod (28) extending between upper and lower tie plates, and having at least one fuel rod spacer (44) located along the non-round water rod, includes cooperating components (38,40) on the fuel rod spacer (44) and on the water rod (28) for permitting movement of the spacer along the water rod to a desired axial location and for thereafter preventing further axial movement of the spacer in at least one of two opposite axial directions, the cooperating components including at least one spring (38) either on the spacer or on the water rod.

Description: The present invention relates generally to nuclear reactor fuel bundle assemblies, and particularly, to the manner in which fuel rod spacers are axially fixed on non-round water rods within the assembly. In boiling water nuclear reactors, fuel rods are grouped together in an open-ended tubular flow channel, typically referred to as a fuel assembly or bundle. A plurality of fuel assemblies are positioned in the reactor core in a matrix and a coolant/moderator flows upwardly about the fuel rods for generating steam. The fuel rods are supported between upper and lower tie plates in side-by-side parallel bundles. One or more water rods are usually centered within each fuel rod bundle. Spacers are employed at predetermined elevations along each fuel bundle to restrain the fuel rods from bowing or vibrating during reactor operation. Typical spacers often include a plurality of ferrules arranged in side-by-side relation and secured, for example, by welding to one another to form a support matrix for the fuel rods. Generally, the role of the spacer in a fuel bundle assembly is to maintain the rods in fixed location relative to one another. These spacers must be secured or captured in some way so as to prevent their movement along the longitudinal axis of the bundle, during operation of the reactor. The traditional method of maintaining fuel rod spacers in position along the axis of the bundle includes the use of small tabs welded to the water rods. Water rods have generally been of round cross section, and the assembly process is predicated on the ability to rotate the water rod after the spacers have been aligned, so that the tabs prevent axial spacer movement Water rods with non-round cross sections, however, cannot be rotated relative to the spacer. U.S. Patent No. 5,149,495 describes one technique for locating spacers along non-round water rods. The technique there employs a recess on a portion of an exterior surface of a water rod, the recess being defined within a protrusion extending from the water rod either integrally or attached as by welding, brazing or other suitable means. The configuration of the water rod is such that the position of the recess with respect to the spacer can be changed by resilient deflection of the water rod itself. In other words, there is enough resilience in the water rod that a portion of the side wall near the recess can be inwardly deflected to effect movement of the recess portion during attachment of the spacer. Once the spacer is in place, the resiliency of the water rod permits spring back of the water rod side wall to substantially its original shape for engagement of the recess portion with a mating projection on the spacer. While this technique is acceptable in some circumstances, there are instances where the water rod wall thickness is too great to permit the necessary degree of deflection. EP-A-0.516,307 discloses a nuclear fuel assembly having a plurality of fuel rods and a non-round water rod extending between an upper and a lower tie plate. The fuel assembly also includes at least one spacer which is fixed to the water rod by spring means. The spring permits movement of the spacer along the water rod to a desired axial position whereafter the spring snaps into an opening and prevents further axial movement of the spacer. EP-A-0,681,299 discloses a similar fuel assembly having a non-round water rod and a spacer. A spring element on the spacer is captured in a locking groove in the side of the water rod. JP-A-02,173,594 discloses a fuel assembly having a square water rod and at least one spacer fixed by means of an elastic hooking member to the water rod. According to the present invention, there is provided a nuclear reactor fuel bundle assembly having a plurality of fuel rods and a non-round water rod extending between upper and lower tie plates and having at least one fuel rod spacer located along the non-round water rod, and cooperating means on said fuel rod spacer and on said water rod for permitting axial movement of said spacer along said water rod to a desired axial location and for thereafter preventing further axial movement of said spacer in at least one of two opposite axial directions, said cooperating means including at least one spring on said spacer, characterised by at least one tab on said water rod, said at least one tab being arranged to engage and thereby limit axial movement of the spacer along the water rod, and said at least one tab being located on a side of the water rod opposite that side which is engageable by said spring, thereby permitting said spacer to be biased in a lateral direction away from said at least one tab and perpendicular to a longitudinal axis of said water rod so that, during assembly, said spacer can be moved axially along the water rod past the at least one tab. The fuel bundle of this invention provides spacer capture mechanisms for square or other non-round water rods that has the characteristics and advantages of the mechanism typically used with round water rods. Specifically, the spacer capture mechanisms in accordance with this invention are designed to be simple, fast and reversible during the assembly process (spacers are rarely removed once the reactor becomes operational), while at the same time strong enough to secure the spacers against the forces encountered during assembly, transport, operation and maintenance. The design also permits disassembly of the bundle in a reactor fuel storage pool before or after irradiation. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- FIGURE 1 is a partial section view of a conventional boiling water nuclear reactor fuel bundle assembly; FIGURE 2 is a partial side elevation of a spacer secured to a round water rod; FIGURE 2B is a plan view of Figure 1 illustrating the water rod in a first assembly position; FIGURE 2C is a plan view similar to Figure 2B but with the water rod rotated to a spacer retention position; FIGURE 3 is a schematic side view of a spacer and water rod incorporating a spacer retention mechanism as shown in a first spacer assembly position in accordance with an embodiment of the invention; FIGURE 3A is a view similar to Figure 3 but illustrating the spacer in a fixed non-assembly position; and Referring now to Figure 1, there is illustrated a nuclear fuel assembly, generally designated 10, including a plurality of fuel rods 12 supported between an upper tie plate 14 and a lower tie plate 16. The fuel rods 12 pass through a plurality of fuel rod spacers 18 at vertically spaced positions along the fuel bundle. Spacers 18 provide lateral support to retain the elongated fuel rods 12 in spaced relation relative to each other, and to restrain the fuel rods from lateral vibrations. Typically, the fuel rods are arranged in a 10x10 array, but the number of rods in the array may vary and the spacer retention mechanism of this invention are equally applicable to arrays containing any number of rods. Typically, one or more water rods ( not shown in Figure 1) are located within the fuel rod bundle and serve as a mounting location for the plurality of spacers 18. Turning to Figure 2, 2B and 2C, a conventional spacer-to-water rod retention mechanism for a round water rod is schematically illustrated. Specifically, the water rod 20 is provided with vertically (or axially) spaced tabs 22, 24, which are welded or otherwise secured to the rod 20. A spacer 26 is slidably engaged on the water rod and, in the assembly position, the water rod 26 is oriented as shown in Figure 2B so that the tabs 22, 24 do not interfere with the sliding motion of the spacer 26. Figure 2C illustrates the manner in which, once the spacer 26 is properly oriented along the length of the water rod, the water rod 20 may be rotated so that the tabs 22 and 24 are located to restrain any further axial movement of the spacer relative to the rod. Tuming now to Figure 3, a square or otherwise non-round water rod 94 is provided on one flat side 96 thereof with a pair of tabs 98, 100 similar to those used with conventional round water rods. The tabs 98 and 100 are spaced axially along the water rod 96 so that a spacer 102 can be axially located therebetween. In this case, however, an interior vertical wall 104 of the spacer 102 is provided with a compression spring 106 which allows the spacer 102 to be moved laterally relative to the water rod, against the spring bias, to the position shown in Figure 3. In this position, the spacer 102 is free to move axially along the length of the rod 96 without interference until it is positioned between the tabs 98 and 100. Once the spacer 102 is properly oriented, the spacer is released to spring back to its centered operating position as shown in Figure 3A with the tabs 98 and 100 effectively preventing axial movement the spacer 102 relative to the water rod 94.

Claims: A nuclear reactor fuel bundle assembly (10) having a plurality of fuel rods (12) and a non-round water rod (94) extending between upper and lower tie plates (14, 16) and having at least one fuel rod spacer (102) located along the non-round water rod, and cooperating means on said fuel rod spacer (102) and on said water rod (94) for permitting axial movement of said spacer along said water rod to a desired axial location and for thereafter preventing further axial movement of said spacer in at least one of two opposite axial directions, said cooperating means including at least one spring (106) on said spacer, characterised by at least one tab (98, 100) on said water rod, said at least one tab being arranged to engage and thereby limit axial movement of the spacer along the water rod, and said at least one tab being located on a side of the water rod opposite that side which is engageable by said spring, thereby permitting said spacer to be biased in a lateral direction away from said at least one tab and perpendicular to a longitudinal axis of said water rod so that, during assembly, said spacer can be moved axially along the water rod past the at least one tab. The fuel bundle assembly of claim 1 wherein said at least one tab comprises a pair of tabs (98, 100) arranged to capture the spacer therebetween so as to prevent further axial movement of said spacer in two opposite axial directions.

Inventors: CROTEAU EDWARD ARMAND, ELKINS ROBERT BRUCE, FREDERICKSON CHRISTIAN DAVID, HARMON JOHN LEE, HIGGINS RUSSEL PATRICK, KING HAROLD BLECKLEY, LATTER GERALD MARTIN, PATTERSON RICHARD GEE, REESE ANTHONY PAUL, WHITE DAVID WILLIIAM, CROTEAU, EDWARD ARMAND, ELKINS, ROBERT BRUCE, FREDERICKSON, CHRISTIAN DAVID, HARMON, JOHN LEE, HIGGINS, RUSSEL PATRICK, KING, HAROLD BLECKLEY, LATTER, GERALD MARTIN, PATTERSON, RICHARD GEE, REESE, ANTHONY PAUL, WHITE, DAVID WILLIIAM
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1997
Main classification: G21C3
IPC codes: G21C3