Thermal hydraulic analysis of in-vessel loss of coolant accident for the EAST lower divertor primary heat transfer system

Uneven heat load distribution on the divertor during the high power long-pluse discharge of the Experimental Advanced Superconducting Tokamak (EAST) leads to hot spot phenomena, potentially causing the Plasma Facing Component (PFC) material melting, flaking, and even penetration, which may trigger the in-vessel loss of coolant accident (LOCA). Continuous coolant intrusion could damage vacuum equipment, while flash evaporation may increase vacuum pressure, posing a potential threat to the safety of the device operation. In this research, the RELAP5/MOD3.4 program was employed to develope a model of the lower divertor primary heat transfer system (PHTS). Steady state analysis was conducted to obtain the key parameters of the system in comparison with the design parameters, and the results showed good consistency. Thermal-hydraulic analysis of the in-vessel LOCA is performed based on the design condition, quantitatively investigating the evolution of the breach discharge flow rate and vacuum pressure. An additional pneumatic isolation valve and check valve are proposed as an accident mitigation scheme, and the effectiveness is evaluated to provide a reference for the upgrade of EAST lower divertor PHTS.