Design and life assessment of first wall components

The first wall (FW) of a tokamak fusion reactor is subjected to periodically changing large heat fluxes. Water-cooled FW panels made from austenitic SS 316 L steel are analyzed. First, life predictions for initially defect-free components, obtained by applying design code rules, are compared with experimental results. It is shown that designing by code is very conservative under thermal fatigue. Secondly, a fracture mechanical analysis of the ITER-CDA FW is presented using linear-elastic and elastic-plastic approaches. Fatigue growth of pre-existing cracks is considered. Problems of FW composite structures of dissimilar materials are addressed. The mismatch in the thermal expansion coefficients give rise to residual stresses during the joining process, and leads to a jump in the stress at the interface. Moreover, different elastic properties result in stress singularities at free boundaries or at interface corners.