Abstract: A method is designed to predict the configuration of the corium pool in the lower plenum of reactor vessel. It takes into account both thermo-chemical reaction of corium and the influence of different paths of corium relocated from core region into the lower plenum. The prediction by this method is consistent with MASCA experimental results and is applied to investigate the corium configuration of a reactor which is subjected to a hypothetical station blackout（SBO） accident. It is shown that for the sideward relocation, the configuration shows a three-lay corium pool. The composition in each layer is calculated based on the thermo-chemical data of the materials. The method is designed to predict the integrity of the reactor vessel under IVR condition.