CFD Analysis and optimization of the DEMO WCLL central outboard segment bottom-Cap elementary cell

In the design of magnetic confinement nuclear fusion power plants, the Breeding Blanket (BB) plays a crucial role, since it must fulfil key functions such as tritium breeding, radiation-shielding and removing of the heat power generated by the plasma. The latter task is achieved by the First Wall (FW) and Breeding Zone (BZ) cooling systems, that in the Water-Cooled Lithium-Lead (WCLL) BB employs pressurized water. Different arrangements of BZ coolant conduits have been investigated in the recent past to identify an efficient layout, which could meet the structural materials operational temperature constraint and that could provide the optimal coolant outlet temperature. However, most of the Computational Fluid-Dynamic (CFD) analysis carried out until now have been focused on the equatorial WCLL elementary cell of the Central Outboard Segment (COB). The aim of this work is to broaden the analysis to other relevant locations in the blanket. An assessment of the design of the cooling system of the COB bottom-cap elementary BZ cell has been identified as the top design priority due to its different geometry and thermal loads. The cooling efficiency of the BZ and FW systems is investigated to assess if the coolant appropriate design conditions are matched and the temperature distribution in the cell is analyzed to identify the onset of hot spots. Different layouts of the FW systems are proposed and compared in terms of thermal-hydraulics reliability.