VOID FRACTION IN SIMULATED BWR FUEL ASSEMBLY .1. SPACER EFFECT ON VOID FRACTION AND ANALYSIS WITHOUT CROSS-FLOW

Void measurement of a vertical 4 x 4 rod bundle has been conducted behind a spacer in a steam-water two-phase flow using an advanced X-ray CT scanner and one-dimensional single subchannel analysis without a cross-flow was done. It was found from the experimental results that the cross-sectional averaged void fraction data behind the spacer could be predicted by the drift-flux model, that the spacer has a negligible effect on the cross-sectional averaged void fraction and that EPRI correlation made it possible to accurately predict the void data. In addition, the simplified single subchannel analysis without the cross-flow between subchannels gave good agreement with data of center subchannels in a quality range of 5% or more. However, the analysis predicted higher void fraction than experimental results in the corner subchannel.