Reduced pressure drop spacer for boiling water reactor fuel bundles

Abstract

A spacer array is disclosed in which alternating cells are disposed at differing elevations. In a preferred octagonal spacer cell array, alternate fuel rods within the rows and columns of the fuel bundle matrix are surrounded by octagonal spacer cells at a first elevation. Likewise, and in the same preferred octagonal spacer array, the remaining alternate fuel rods within the rows and columns of the fuel bundle matrix are surrounded by octagonal spacer cells at a second elevation. The octagonal spacer cells of the spacer array at one level adjoin the octagonal spacer cells of the spacer array at an adjacent level. Specifically, each octagonal spacer cell has the top and/or the bottom of as many as four of its eight sides disposed for joinding with one side of as many as four octagonal cells in an adjacent cell layer. Each cell has approximately 0.6 of an inch height, or one-half the 1.2 inch height of the prior art. Physically each cell would have approximately half the height of the prior art cell type spacers. There results a spacer cell array which distributes half of the pressure drop at a first elevation, and the remaining half of the pressure at a second elevation for a projected spacer area of one-half that area of the prior art. Further, and because the two cell arrays making up the spacer are disposed at differing elevations--immediately above and below each other--the produced flow resistance at one level of the spacer cells does not have horizontally immediately adjacent cells. Thus, the cells in one layer do not co-act with adjacent flow frictions to the same extent as the co-action would occur if all flow frictions and restrictions were at the same elevation. There results an improved and lesser pressure drop in the disclosed spacer array.