Y. Yamamoto et al., BOILING TRANSITION PHENOMENON IN BWR FUEL ASSEMBLIES EFFECT OF FUEL SPACER SHAPE ON CRITICAL POWER, Nippon Genshiryoku Gakkaishi, 38(4), 1996, pp. 315-323
A thorough understanding of the thermal-hydraulic phenomena near fuel
spacer is necessary for the accurate prediction of the critical power
of BWR fuel assemblies, and is thus essential for effective developmen
ts of a new BWR fuel assembly. The main purpose of this study is to de
velop an accurate method for predicting the effect of spacer shapes on
critical power. Tests have been conducted under actual. BWR operating
conditions, using an annulus flow channel consisting of a heated rod
and circular-tube channel, and BWR simulated 4x4 rod bundles with heat
er rods unheated just upstream of spacer. The effect of spacer shapes
on critical power was predicted analytically based on the droplet depo
sition rate estimation. The droplet deposition rate for different spac
er shapes was calculated using a single-phase flow model. The predicti
on results were compared with the test results for the annulus flow ch
annel using ring-type spacers. Analytical results of critical power ag
reed with measured critical power from point of the effects of changes
in the rod-spacer clearance and the spacer thickness on critical powe
r.