Structural assessment of a whole toroidal sector of the HELIAS 5-B breeding blanket

Abstract

The European roadmap for the realization of fusion energy considers the stellarator line as a possible long-term alternative to a tokamak DEMO. In this context, from the plasma physics standpoint, the most promising option is a five-field period power plant called HELIcal-axis Advanced Stellarator (HELIAS) 5-B. In order to allow the electricity production, the HELIAS 5-B reactor must be endowed with a breeding blanket (BB). Hence, in this paper, the advancements in the HELIAS 5-B BB design are reported. In particular, the structural assessment of a whole BB period, extending along toroidal direction for 72 °, is depicted. A geometric configuration encompassing dummy BB segments has been set up to verify the feasibility of the proposed BB segmentation strategy for the whole sector. Both the Helium Cooled Pebble Bed (HCPB) and Water Cooled Lithium Lead (WCLL) BB concepts have been considered. Results have shown that, in principle, the occurrence of overlapping between adjacent segments depends on the BB-Vacuum Vessel connection mode, regardless of the considered BB concept, and on their mutual thermal expansion. Then, focusing only on the HCPB BB concept, a preliminary detailed geometric design of two BB segments, located at the inboard region of a bean shaped ring, has been carried out in order to investigate their structural behavior under steady state accidental loading conditions. To this end, the stress field arising within the structure of the two segments has been assessed following the RCC-MRx structural design rules. Results have shown that the proposed design works quite well under the assumed loading conditions. The study has been performed adopting the Finite Element Method and using the Ansys v.19.1 commercial code. The obtained results will be presented and critically discussed.