In-bundle void measurement of a BWR fuel assembly by an x-ray CT scanner: Assessment of BWR design void correlation and development of new void correlation

Void fraction measurement tests for BWR fuel assemblies have been conducted as a Japanese national project mainly to prove the current BWR design void prediction method. The purpose of this study is to evaluate the BWR design void correlation and to develop the new void correlation. Void fraction was measured by the X-ray CT scanner. The tests have been carried out in an out-of-pile test facility that can simulate the high pressure and high temperature conditions of BWRs. An electrically heated test assembly simulates a BWR fuel assembly on a full scale. It was found that the void fractions predicted by the BWR design void correlation agree closely with the test measurements and the prediction accuracy was △̄α (average of difference between measure and calculation) = 2.1 % and σ (standard deviation of △̄α) = 3.0 %. In addition the new void correlation has been developed based on the drift flux model, and the prediction accuracy was △̄α = 0.3 % and σ = 1.9 %. The agreement with the published void data was fairly good.