Numerical and experimental analysis of transient wave propagation through perforated plates for application to the simulation of LOCA in PWR

Loss of coolant accident is characterized by a transient rarefaction wave propagating inside the primary loop after pipe break, resulting in fluid loading on internal structures, especially on the baffle surrounding the reactor core. In that case, loading comes from differences in rarefaction wave travel times, whether it propagates through the reactor core or through the by-pass between baffle and core barrel, yielding delays and pressure differences on both sides of baffle plates. Propagation is strongly influenced by geometric obstacles such as holes in baffle reinforcement plates, which cannot be represented in a numerical model of the whole primary loop and has then to be replaced by suitable impedance relations. A methodology to validate and calibrate such impedance models, based on specific experimental results and high-order CFD simulations, is thus proposed. Models are tested and integrated into EUROPLEXUS fast-transient fluid–structure dynamics software.