Preliminary thermal optimization and investigation of the overall structural behaviour of the EU-DEMO water-cooled lead lithium left outboard blanket segment

The conceptual design phase of the EU-DEMO reactor has been recently launched, with the aim of evolving the DEMO pre-conceptual layout towards a more robust and articulated geometric configuration able to cope with most of the design requirements and to show further margins for the passing of the current potential show-stoppers. Hence, the achievement of the conceptual design of the Water-Cooled Lead Lithium Breeding Blanket (WCLL BB) is one of the milestones the EUROfusion consortium aims to achieve in the close future. To this purpose, within the framework of the research activities promoted by EUROfusion, a research campaign has been launched at the University of Palermo, in close cooperation with ENEA-Brasimone, in order to investigate, from the thermal and thermomechanical standpoints, the WCLL BB Left Outboard Blanket (LOB) segment performances. The scope of the analysis carried out has been the advancement of the WCLL LOB segment design in view of the prescribed thermal and structural design requirements. To this end, the nominal WCLL BB operating conditions as well as accidental steady-state scenarios derived from the in-box loss of coolant accident and the upper vertical plasma disruption event have been considered. In the first part of the study, the internal Double-Walled Tubes (DWTs) layout of the WCLL LOB equatorial region have been preliminarily optimized so to find a geometric configuration able to cool the segment structure maintaining the maximum temperature below the suggested limit of 550 °C. Then, a purposely set-up analytical procedure has allowed obtaining a set of interpolating functions able to accurately reproduce the calculated thermal field and to extrapolate it to the whole WCLL LOB segment. Afterwards, the thermo-mechanical analysis of the entire segment has been performed under the selected loading scenarios. The structural behaviour of the segment has been assessed in compliance with the RCC-MRx code, adopting the set of criteria on the basis of the nature of the considered loading scenario. The obtained results, herewith presented and critically discussed, have allowed introducing significant design improvements with respect to the WCLL LOB segment reference geometric layout, coming from the pre-conceptual design phase, paving the way for future, and more detailed, structural investigations.