Investigation on cooling performance of WCLL breeding blanket first wall for EU DEMO

Highlights: • The cooling capability of WCLL BB FW is analyzed under the reviewed EU DEMO heat flux specifications. • The optimization is carried out modelling the FW structure and cooling system. • The thermal hydraulic analysis under the heat flux of non-uniform distribution is performed. • The present WCLL BB FW design is far away from DNB occurrence. -- Abstract: The Breeding Blanket (BB) First Wall (FW) is the first boundary separating the fusion plasma and its energetic particles from the rest of a Tokamak. The heat load specifications at different poloidal positions are reviewed according to the maximum heat load (surface radiation and charged particles). In the framework of the European Demonstration (EU DEMO) fusion reactor work package for BB, the cooling performance of the Water-Cooled Lithium Lead (WCLL) BB FW is investigated using a Computational Fluid Dynamics (CFD) approach. The reference geometry is compared with different FW geometries and cooling schemes. The configuration with two passes has better cooling performance and the coolant velocity is lower than the limit (i.e., 7 m/s). Compared with the square channels, the circular design highlighted a higher temperature hot-spot in the structural material. Under the non uniform heat flux (HF) distribution, the structure temperature exceeds the upper limits at the FW elbows of the Inboard Blanket (IB) 5, 6,7, plus the upper part of IB4, where the HF is beyond 1.34 MW/m². The current WCLL FW design is far away from the occurrence of Departure from Nucleate Boiling (DNB). In general, the present design of the FW can maintain the temperature of the structure below the limit and ensure the design coolant temperature at the channel outlet (i.e., 328 °C).