Transient pressure propagation behavior in PbLi loop system triggered by in-box LOCA accident of DFLL blanket

•Propagation of pressure wave in PbLi Loop System under in-box LOCA accident was studied with coupling method.•The peak pressure in the blanket module was much higher than the operating pressure of He loop system.•Due to the pressure relief effect of the PbLi tank and the expansion vessel, the key components in PbLi loop were protected. In-box LOCA accident is considered as a Design Basis Accident (DBA) of a fusion blanket because of its frequency and serious consequence. For a liquid metal blanket such as Dual-Functional Lithium Lead (DFLL) blanket, in-box LOCA not only causes pressurization in breeder box, but also propagates transient high pressure to Lithium Lead (PbLi) loop system. Similar to the water hammer effect in the coolant loop of a fission power plant, a high pressure wave in PbLi loop might damage components and threaten the integrity of loop structure. In this paper, the 3D Computational Fluid Dynamics (CFD) code FLUENT was coupled with the systems code RELAP5/MOD4.0 to simulate pressure propagation behavior triggered by an in-box LOCA accident in the PbLi loop system of a DFLL blanket. Reflection and superposition of the pressure wave in complex channels of a DFLL blanket module were accurately simulated with FLUENT, and propagation of pressure waves in the PbLi loop system was simulated by RELAP5 code. The coupling code, which linked FLUENT and RELAP5, transferred the pressure at the inlet/outlet interface of the blanket module to the PbLi loop. Simulation results showed that at the initial stage, the transient peak pressure at the monitoring points in the blanket module reached 14.454 MPa, and the transient peak pressure at the inlet/outlet of the blanket module were 9.612 MPa and 14.454 MPa respectively. Then the high pressure waves propagated to the PbLi loop, and triggered the opening of a blasting valve which connected the low-pressure PbLi tank to the PbLi main loop. The low-pressure PbLi tank acted as a water hammer arrestor and eliminated high pressure in the main loop pipe, which protected the downstream components.