A Modified Simulation Model of Blocked Regions After Rod Cladding Deformation During LOCA Transient

Abstract

During a loss-of-coolant-accident (LOCA) transient, the ballooning and burst of the cladding can lead to blockage of flow path and worsen core coolability. Studies have shown that the core coolability is not changed much up to about 60% blockage ratio, while can be threatened by a severe blockage with a high blockage ratio and long blockage length. A blockage simulation model based on the non-coplanar assumption is widely used in LOCA transient analysis. However, regarding the coplanar deformation observed in experiments, validity of this assumption is questionable. Furthermore, it is found that this model cannot predict reasonable results for severe blockage conditions. In this paper, the blockage model is modified for the thermal hydraulic simulation of LOCA transients with the occurrence of severe blockages. Pre-test simulations of a test facility studying the influence of blockage on core coolability have been conducted with the modified model. The results show that, the modified model shows better agreement with the observations in the experiments.