Parametric study of the influence of double-walled tubes layout on the DEMO WCLL breeding blanket thermal performances

Within the framework of the EUROfusion activities regarding the EU-DEMO Breeding Blanket (BB) concept, the University of Palermo is long-time involved, in close cooperation with ENEA, in the design of the Water Cooled Lithium Lead (WCLL) BB, that is one of the two concepts under consideration for the DEMO reactor. It is mainly characterized by a liquid lithium-lead eutectic alloy acting as breeder and neutron multiplier, as well as by subcooled pressurized water flowing as coolant under PWR-like conditions (pressure of 15.5 MPa and inlet/ outlet temperatures of 295 degrees C/328 degrees C). A research campaign has been recently carried out to study the potential influence of the Breeding Zone cooling circuit layout, composed of bundles of Double Walled Tubes (DWTs), on the blanket thermo-mechanical behaviour. In the first phase, a parametric study has been performed to investigate the effects of some geometrical DWT parameters onto the blanket thermal response in order to identify the best tubes layout, in case arranged along toroidal-radial planes. In the second phase, the thermo-mechanical performances of the blanket equatorial region, equipped with the optimized DWTs layout, have been assessed. The study has been carried out following a theoretical-numerical approach based on the Finite Element Method and adopting the ABAQUS v. 6.14 commercial code. Model, assumptions and results obtained are herewith presented and critically discussed.