Rationale and Method for design of DEMO WCLL Breeding Blanket Poloidal Segmentation

One of the most critical components in the design of DEMO Power Plant is the Breeding Blanket (BB). Currently, four candidates are investigated as options for DEMO. One of these is the Water Coolant Lithium Lead (WCLL) Breeding Blanket (BB). A new WCLL BB concept design has been proposed and investigated in 2015. The first activity driving the BB design was the definition of the poloidal segmentation. Current trend in breeding blanket designs is based on the multi module box approach, which has advantages in terms of manufacturing, in reducing the global stress and strain during the start-up and the shut-down phases and during operation, because the avourable thermal expansions; and in simplifying the First Wall (FW) layout and integration. Nevertheless, drawbacks are identified, such as the reduction of Tritium Breeding Ratio (TBR), the constraints in manifold and in Back Supporting Structure (BSS) design and integration because the limited space available. The present work concerns a method that, starting from these constraints, defines and optimizes some of the main design drivers for the selection of the segmentation of the WCLL BB. The method by definition is based just on geometrical parameters because it is used as first step of the design when any analysis and detailed data are available. It is based on the definition of Figures Of Merits (FOM), consisting in numerical parameters, such as the ratio between the modules volume and the overall volume of segment assigned, the approximation between the real profile of the modules and the theoretical one, the form factor of the modules, the ratio between the module thickness at the mid-plane and the segment thickness at the same position. The FOM support the choice among different options. In particular two different solutions of poloidal segmentation have been compared and, according to the proposed method, the best one was chosen for the design of WCLL BB.