Helical-shaped double wall tubes solution for the breeding zone cooling in the WCLL breeding blanket

One of the two most promising Breeding Blanket (BB) concepts to be chosen as driver design of the EU-DEMO fusion reactor is the Water-Cooled Lead Lithium (WCLL) BB. A crucial point of this key component is the cooling of the BB structural elements and of the Lithium-Lead alloy, used as neutronic multiplier and Tritium breeder. Indeed, the high neutronic flux needed for breeding implies high volumetric power affecting the Breeding Zone (BZ) materials. The current BB layout employs water-cooled Double Wall Tubes (DWTs) with a C-shaped configuration for the BZ cooling. Despite the WCLL BB have reached a mature design in the last years, some open issues remain to be solved to increase the reliability and performance of this technology. The present paper describes a promising upgrade of the BZ cooling layout adopting helical-shaped DWTs. This solution has the potential to increase the BB reliability, cooling performance, Tritium Breeding Ratio and cooling water flow-path simplicity. The new proposed layout is described in the paper, along with results of CFD analyses carried out to investigate the new cooling performances in BZ. Advantages and drawbacks with respect to the current BB layout have been also highlighted in the paper.