Pool scrubbing and hydrodynamic experiments on jet injection regime

摘要

Plant analyses have shown that pool scrubbing can play an important role in source term during PWR risk dominant sequences. Examination of boundary conditions governing fission products and aerosols transport through aqueous beds revealed that most of radioactivity is discharged into the pool under jet injection regime. This fact and the lack of experimental data under such conditions pointed out the need of setting out an experimental programme which provided reliable experimental data to validate code models. In this report results of a pool scrubbing experiment carried out in PECA facility are presented. One major finding was that a remarkable fraction of particle absorption was not a function of the residence time of bubbles rising through the pool. Such a contribution was assumed to be associated to aerosol removal at the pool entrance. As a consequence, a hydrodynamic experiment was launched on gas behaviour during initial stages in the pool. Nuclei size and shape in the pool were measured and fitted to a long normal distribution. Size was found to be sensitive to inlet gas flow and, to a minor extent, to gas composition and pool temperature. SPARC90 and BUSCA-AUG92 were used to simulate the retention tests. Whereas SPARC90 showed fairly good agreement with experimental data, BUSCA-AUG92 results were far away from measurements in all the cases. SPARC90 consistency apparently pointed out the important role of fission products and aerosols retention at the injection zone; nonetheless, peer examination of pool scrubbing phenomenon at the pool entrance should be carried out to test both hydrodynamic and removal models. Hence, there is a need for further research under representative severe accident conditions (saturated pools, jet injection regimes, etc.), as well as separate effect tests to validate, improve and/or develop specific models for the pool entrance region.