Flow Analyses Using RELAP/MOD3.3 Code for the Simulant Melt Experiments (LAVA-ERVC) Under the External Reactor Vessel Cooling

Flow analyses using RELAP5/ MOD3.3 code have been performed to investigate the occurrence and the effects of steam binding for the LAVA-ERVC experiments. The main objectives of the LAVA-ERVC experiments are investigations of coolability through external reactor vessel cooling according to RPV insulation design. It could be found from the sensitivity studies for the flow path in the annulus of insulation that steam binding could occur in case of the limited steam venting capacity, which is definitely coincident with the LAVA-ERVC experimental results. In case of sufficient flow path for the steam venting, the vessel experienced effective cooling by nucleate boiling heat transfer. And existence of the upper free volume had little effect on occurrence of steam binding in the LAVA-ERVC experiments.