Subchannel void-fraction measurements in a 6 x 6 rod bundle using a simplegamma-transmission method

A relatively simple subchannel void-fraction measurement system was develop ed and applied to a scaled model of a BWR fuel assembly. The measurement sy stem is based upon the gamma-transmission technique and uses a tomographic reconstruction procedure to calculate the void-fractions in the subchannels , Data pre-processing is used to remove positioning errors of the gamma sou rce and detector. Measurements are performed under different operating cond itions and radial power profiles. The measurements are compared with the dr ift-flux two-phase flow model. The void-fraction in the wall and corner sub channels is lower than average. By applying the drift-flux model to each su bchannel separately and comparing this calculation with measurements the pr esence of lateral void-drift should be detectable. However, the data do not show evidence for lateral void-drift. By comparing two chordal void-fracti ons, one through the fuel rods and one in between the fuel rods, a flow pat tern transition could clearly be seen between a void-fraction of 30% and 40 %. (C) 2000 Elsevier Science Ltd. All rights reserved.