| 摘要 |
<p>An improved lower tie plate (L) having increased fluid flow resistance is disclosed for use in a boiling water nuclear reactor. The fuel bundle includes the lower tie plate, an upper tie plate, and a plurality of fuel rods (R) supported therebetween in vertical upstanding relation. The fuel rods are surrounded by a channel which confines the fluid flow through the fuel bundles between the tie plates for the extraction of heat from the fuel rods undergoing a fission reaction. The lower tie plate includes a first group of support locations for the fuel rods in selected positions in a matrix. The matrix may be interrupted at larger apertures for the support of moderator containing water rods. The tie plate also includes a second matrix of through holes (70) acting as fluid energy dissipation orifices. These fluid energy dissipation orifices include a first small downwardly exposed fluid receiving aperture which discharges to a second and larger upwardly exposed flow area preferably formed in the shape of a concentric aperture. In the preferred embodiment the inlet to the first concentric and small downwardly exposed fluid receiving aperture is rounded for the intake of fluid with maximum flow predictability. The transition between the two apertures produces predictable energy dissipating turbulence in the upwardly exposed fluid discharge area. Passage of fluid through the energy dissipation apertures causes an increased pressure drop at the lower tie plate, for the suppression of thermal-hydraulic flow instabilities, and coupled thermal-hydraulic nuclear instabilities. A serendipitous effect is present in that the increased pressure drop causes uniform fluid flow in the interior of the fuel bundle immediate the lower tie plate.</p> |
