Two-phase pressure drop reduction BWR assembly design

摘要

In a boiling water reactor having discrete bundles of fuel rods (65) confined within channel enclosed fuel assemblies, an improved fuel design of bundles of fuel rods interior of the channels is disclosed. Specifically, partial length rods (60) are utilized which extend from the bottom of the channel only part way to the top of the channel. These partial length rods (60) are shortened with respect to the remaining rods (65) and are symmetrically distributed throughout the fuel bundle with the preferred disposition being in the second row of the bundle of fuel rods from the channel wall. The symmetrical distribution of the partial length rods is at spaced apart locations one from another. The partial length rods extend from the bottom of the fuel bundle and terminate within the boiling region. During shutdown of the reactor, an improved cold shutdown margin is produced at the top of the fuel assembly due to the improved moderator-to-fuel ratio and reduction in plutonium formation at the upper portion of the bundle. Rod spacers (S) and bundle tie plates (40,42) are provided with larger apertures (67) overlying the partial length rods for further channeling of the steam and reduction of two-phase pressure drop.