Application of a multiphysics simulation tool to an in-box LOCA in the WCLL TBM test section of the LIFUS5/Mod4 facility

In the design of the Water Cooled Lithium Lead Breeding Blanket, a critical concern is the in-box Loss of Coolant Accident (LOCA). Extensive research, both experimental and numerical, has been devoted to understanding the interaction between Lithium-Lead and Water and its implications for the overall system. To simulate this complex scenario, the SIMMER code, originally developed for Liquid Metals, was chosen. However, SIMMER alone cannot handle complex pipeline geometries. In contrast, RELAP5, a thermal-hydraulic system code, is well suited for these kinds of geometries and it is intensively used in the nuclear industry. A coupling methodology was developed, combining the strengths of both codes. The simulation involved a geometry resembling the ITER TBM BU test section using SIMMER-IV for nodalization, while RELAP5/Mod3.3 modeled the piping system of the new Integral Test Facility under construction at ENEA CR Brasimone, called LIFUS5/Mod4. This work shows that the coupling between the two codes achieved high synchronization in steady-state conditions and successfully replicated a fast transient in-box LOCA scenario. The results show the pressure propagation along the entire Lithium-Lead loop generated by the accidental scenario. The simulation outcomes, though preliminary from a technical point of view shows that the pressure wave is dampened due to the overall system compressibility. This coupling tool proves invaluable for supporting facility design and safety assessments of the WCLL breeding blanket design.