Off-Take Experiment at T-Junction Between Header and Feeder Pipes in CANDU Reactors

Abstract

An experimental study has been performed to investigate the off-take phenomena at the horizontal pipes branched with various angles, +/- 36 degrees and +/- 72 degrees between the fuel channel header and feeder pipe in a CANDU 6 reactor. In safety analyses for transient simulation, the current horizontal stratification entrainment model (HSEM) inside RELAP5/MOD3.3 code cannot predict the exact mass qualities at specific angle branches because it can be applied only at the bottom, top and side branches. Therefore, the geometrical characteristics between header and feeder pipes requires different approaches to safety analysis from the current simulation codes developed for light-water cooled reactors. To develop a bestestimated transient simulation code for CANDU reactors, there is a need to develop the HSEM based on actual angles. In this experimental study, off-take experiments are carried out using the experimental facility of horizontal pipe with 7 angled branch pipes. The header and feeder pipes in CANDU 6 are scaled down to design the off-take test faci lity to a CANDU-6 reactor considering the geome tric effect of branching angles. Three different diameters and seven different angles of branch pipes are used to verify their scale and geometry effects. The off-take phenomena - liquid/gas entrainment - are observed for various angles between the header pipe and feeder pipe. The HSEM and the experimental results of previous studies are validated by the present experimental data for three branch orientations. The data of onset of off-take shows agreements with the existing correlations. However, the experimental results show that HSEM does not show good agreement of the present onset data of the specific branch angles, +/- 36 degrees and +/- 72 degrees, and the quality data show discrepancies in top and bottom branches.