Modification on the contact model of LiPb and noncondensable gas in RELAP/SCDAPSIM/MOD4.0 and application to LOCA of China DFLL-TBM

Highlights: • The thermo-physical and transport properties of LiPb vapor phase are implemented into RELAP/SCDAPSIM/MOD4.0 code. • In-TBM breeder box coolant leak accident analysis has been carried out for China Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM). • The extended RELAP/SCDAPS/MOD4.0 code can be used for the DFLL-TBM system safety analysis in the future. - Abstract: In-TBM breeder box coolant leak is one of four reference accidents identified for China Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM), which will result in the pressurization of the TBM LiPb breeding zones and cooling system. In order to analyze In-TBM breeder box coolant leak accident, there is a need to simulate the mixing of liquid metal and non-condensable gas. While the current system safety code RELAP/SCDAPSIM/MOD4.0 which was initially designed to predict the behavior of light water reactor systems is incapable of modeling the mixture of liquid metal fluids and non-condensable gas. This paper first briefly introduce the reason for RELAP/SCDAPS/MOD4.0's incapability of modeling liquid metal in contact with a non-condensable gas. Then, a solution to solve the problem and the modification of the RELAP/SCDAPSIM/MOD4.0 code is proposed. Several typical problems involving liquid metal in contact with helium were simulated and the results demonstrate the feasibility and validity of the modified RELAP/SCDAPS/MOD4.0 in modeling the mixing of liquid metal and non-condensable gas. Last but not least, the modified RELAP/SCDAPS/MOD4.0 is used for transient analysis of In-TBM breeder box coolant leaks. Since both lead-lithium eutectic alloy and helium serve as TBM coolants, the Lithium Lead Cooling System (LLCS) and the Helium Cooling System (HCS) were modeled to investigate the thermal-hydraulic characteristic of the TBM system and its influence on ITER safety under the accident conditions. Results show that LLCS pressurization during In-TBM breeder box coolant leak is adequately handled by the safety accessories provided in LLCS and the highest temperature of the first wall is far below its melting point during the accident process.