Aiming at understanding thermo-mechanical loads in the first wall of DEMO: Stress–strain evolution in a Eurofer-tungsten test component featuring a functionally graded interlayer

• Published in: Fusion engineering and design 2018-10, Vol.135, p.141-153
• Main Authors: Heuer, S., Weber, Th, Pintsuk, G., Coenen, J.W., Matejicek, J., Linsmeier, Ch
• Format: Article
• Language: English
• Subjects: Armor; Boundary conditions; Deformation; Deformation mechanisms; DEMO; Electric power generation; Evolution; Fe/W; Ferritic stainless steels; Finite Element Analysis; First wall; Functionally graded materials (FGM); Functionally gradient materials; Fusion; Interlayers; Loads (forces); Martensitic stainless steels; Mathematical models; Mechanical properties; Nuclear fusion; Nuclear power plants; Plastic deformation; Power plants; Shear stress; Strain; Stresses; Tungsten
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2018.07.011

For the future fusion demonstration power plant, DEMO, several blanket designs are currently under consideration. Despite geometric and operational differences, all designs suggest a first wall (FW), in which tungsten (W) armour is joined to a structure made of Reduced Activation Ferritic Martensitic (RAFM) steel. In thermo-mechanical analyses of breeding blankets, this joint has received limited attention. In order to provide a basis for better understanding of thermally induced stresses and strains in the FW, the thermo-mechanical behaviour of a water-cooled test component is explored in the current contribution. The model aims at providing a simple geometry that allows straightforward comparison of numerical and experimental results, while trying to keep boundary conditions as realistic as possible. A test component with direct RAFM steel-W joint, and a test component with a stress-redistributing, functionally graded RAFM steel/W interlayer in the joint is considered in the current contribution. The analyses take production- and operation-related loads into account. Following a detailed analysis of the evolution of stress components and strain in the model, a parameter study with respect to geometric specifications and loads is presented. The analyses show that, even in a small test component, a direct RAFM steel-W joint causes enormous plastic deformation. The implementation of a functionally graded interlayer reduces stresses and strains significantly, but vertical normal stresses at the joint's circumference remain considerable. With the component geometry considered here, the graded interlayer should be at least 1 mm thick and contain 4 sublayers to appropriately redistribute stresses. Beyond a component width of 14 mm, stresses increase strongly, which may pose a risk to the applicability of large-scale FW components, too.