Lower tie plate strainers having double plate with offset holes for

Abstract

In a boiling water nuclear reactor fuel bundle, a debris catching arrangement is disclosed for incorporation within the flow plenum up stream or below the rod supporting grid of the lower tie plate assembly. The device is preferably placed within the lower tie plate flow plenum between the fuel bundle inlet orifice and the rod supporting grid structure supporting the fuel rods; alternate placement can include any inlet channel upstream of the fuel rods including the fuel support casting. Paired plates defining offset holes and bosses are utilized. The bosses are supported at plate webbing between the respective holes. The holes are preferably square in plan with appropriately relieved and rounded corners defining the edges of the webbing. The bosses may be cylindrical, square or rectangular in cross-section. In confrontation of plates to form the debris catching grid, each boss from one plate confronts a hole from the remaining plate. A system of edge ridges in conjunction with the bosses at each plate edge maintains the plates spatially separated with the bosses of each plate spaced from the webbing of the opposite plate. In the preferred embodiment, the plates are captured in the flow plenum of a two part tie plate. There results a three dimensional and sturdy debris catching construction which has low flow resistance through the continuum of defined flow passages while maintaining excellent debris entraining properties.