On the thermal and thermomechanical assessment of the “Optimized Conservative” helium-cooled lithium lead breeding blanket concept for DEMO

Abstract

Within the framework of EUROfusion R&D activities a research campaign has been performed at CEA-Saclay, in close collaboration with the University of Palermo, in order to investigate thermal and thermomechanical performances of the "Optimized Conservative" concept of DEMO Helium-Cooled Lithium Lead breeding blanket (HCLL). Attention has been paid to the HCLL outboard equatorial module (OEM) when subjected to the steady state nominal loading scenario. To this purpose three simplified 3D models, characterized by an increasing level of detail, have been set-up taking into account, firstly, a single radial-toroidal slice, then a basic module geometric unity composed by two adjacent slices and adding, lastly, the peripheral poloidal region. This latter 3D model has allowed the assessment of the Caps potential influence on the module thermal and thermomechanical behaviour.For each investigated 3D model, thermal and thermomechanical analyses have been performed and a stress linearization procedure has been carried out in order to verify the fulfilment of the criteria prescribed by the RCC-MRx 2015 code. The study has been performed adopting a numerical approach, based on the Finite Element Method (FEM), and adopting the Siemens NX v. 10.0 software in order to discretize the geometric domain, whereas thermal and thermomechanical calculations have been carried out using the Cast3M 2015 FEM code.The obtained results, herewith reported and critically discussed, allow predicting a good thermal and mechanical behaviour of the "Optimized Conservative" concept of DEMO HCLL OEM, even if some small modifications to the module cooling scheme should be performed in order to avoid the insurgence of hotspots where temperature is slightly above the Eurofer limit temperature (550 °C). This will entail, from the mechanical point of view, a reduction of the secondary stress amount which is the main responsible of the failure in RCC-MRx criteria verification within First Wall-Side Wall bend region.

Status of the EU DEMO HCLL breeding blanket design development

“…The so called "Optimized Conservative" concept, made of vertical and horizontal Stiffening Plates (vSP, hSP), and CP has been analyzed regarding thermal and mechanical behavior in Ref. [6] and has been demonstrated as a robust solution. However, this design offers very slight margin in term of tritium breeding [7], one of the key requirements for the DEMO BB to reach a Tritium Breeding Ratio (TBR) higher than 1.1 for ensuring the tritium self-sufficiency function [2].…”

“…Within the EUROfusion organization, CEA with the support of Wigner-RCP and Centrum výzkumu Řež, is in charge of the design of the HCLL BB for DEMO. It is based on the use of Reduced Activation Ferritic/Martensitic (RAFM) steel Eurofer as structural material, the eutectic Pb-15.7Li enriched at 90% in 6 Li as tritium breeder and tritium carrier, and helium as coolant with inlet/outlet temperatures of 300/500 °C and 8 MPa pressure. This paper will present the design description of the HCLL BB and its evolution to achieve a new reference design, supported by some neutronic, thermal and mechanical analyses.…”