Cooling Characteristics with Partial Core Blockage during Long Term Cooling Period of Hot-Leg LBLOCA

During a loss-of-coolant accident (LOCA), the coolant is recirculated from a containment sump to a reactor coolant system (RCS). The debris, which is mainly composed of fragments of pipe and insulator stripped off at a break location, can be filtered by sump strainer. Some of debris, however, can pass the strainer and it may collect on the surface of the fuel assembly (FA) bottom nozzle or adhere on the cladding. The collected debris leads to a flow resistance which results in decreasing the coolability at the core. In order to resolve this safety issue, various experimental studies with separate effect test facility and code simulations were performed. The integral effect test data, however, are quite limited. In the present study, a core blockage effect test was performed with a thermal-hydraulic integral effect test facility, ATLAS (Advanced Thermal-hydraulic Test Loop for Accident Simulation). A long term cooling phase of hot leg large break loss of coolant accident (LOCA) was simulated and the core blockage ratio was increased gradually from 0 to 93.2 %. The effect of core partial blockage in terms of core cooling was synthetically investigated with ATLAS. A long term cooling phase of hot LBLOCA was simulated and the core blockage ratio was increased gradually from 0 to 93.2 % in the present test. It can be concluded from the present test results that even though a core inlet is blocked up to 93.2% the core can be effectively cooled.