On thermo-mechanical issues induced by irradiation swelling inside the back-plate of the IFMIF target assembly

Within the framework of the IFMIF R&D program and in close cooperation with ENEA-Brasimone, at the Department of Nuclear Engineering of the University of Palermo a research campaign has been launched to investigate the thermo-mechanical issues potentially induced by irradiation swelling in the threaded connections between frame and back-plate of IFMIF target assembly. The main aim of the research campaign has relied in the assessment of the maximum swelling-induced volumetric strain that may be accepted in order to allow screws to withstand thermo-mechanical stresses and work in safe conditions or to avoid unduly high unscrewing torques during back-plate remotely handled maintenance operations. A theoretical approach based on the Finite Element Method (FEM) has been followed and a quoted commercial code has been adopted to perform the study. Since swelling-induced volumetric strain distribution within back-plate has not yet been assessed, a parametric analysis has been carried out, assuming swelling-induced volumetric strains ranging from 0.001% to 0.1%. A realistic 3D FEM model of a portion of frame and back-plate pertaining to a single screw has been set-up and a realistic set of loads and boundary conditions has been imposed. The results obtained are presented and critically discussed.