Design of the WCLL BB in view of the conceptual design phase

In view of the definition of the driver blanket for the EU-DEMO fusion reactor, three Breeding Blanket (BB) concepts are being studied in the framework of EUROfusion consortium activities. In mid-2020 two of these concepts, the Water Cooled Lead-Lithium (WCLL) and the Helium Cooled Pebble Bed (HCPB), were reviewed by a panel of external experts to assess the design validity, while the third, the Water-cooled Lead Ceramic Breeder (WLCB), has been recently developed as alternative solution. Thus, starting from the outcomes of the Gate Review, several modifications have been introduced to the WCLL BB design with the aim of addressing the issues revealed by the aforementioned panel. The present paper reports on main improvements to the WCLL BB design, such as the new water manifold layout to balance the flow distribution among parallel breeding units, the change of the double-walled tube layout to enhance the BB cooling capability and improve its reliability, as well as design solutions aimed at the improvement of the WCLL BB neutronic and structural performances in terms of tritium breeding ratio and verification of design criteria, respectively. The impact of these changes on nuclear, thermal-hydraulic, MHD and structural performances, as well as on tritium transport, has been evaluated in detail and critically discussed. Finally, the remaining points of improvement are highlighted, giving an overview on possible strategies for their implementation in the WCLL BB design.