COTELS project (3) : ex-vessel debris cooling tests

Test B/C in COTELS project was performed to investigate fuel coolant interaction (FCI) and molten core concrete interaction (MCCI) under water injection onto molten corium. After 60 kg UO2 corium mixture was melted in electric melting furnace (EMF), the corium was fallen into concrete trap. The molten corium in the trap was re-heated to simulate decay heat. When subcooled water was injected onto the molten debris, steam explosion was not observed. Debris was cooled about 20 minutes after water injection and MCCI was suppressed. This favorable cooling was attributed to the existence of remaining porosity inside corium due to simulation of falling process, water ingression via eroded concrete side wall clearance and channels, and the interruption of further concrete floor erosion due to the existence of pebble bed, decomposed from concrete, below the debris. (orig.)