Treatment of irradiation effects in structural design criteria for fusion reactors 1 Work supported

From the standpoint of design criteria for fusion reactors, the most significant issues stem from the irradiation-induced changes in material properties, specifically the reduction of ductility, strain hardening capability, and fracture toughness with neutron irradiation. Recently, Draft 5 of the interim ITER structural design criteria (ISDC), which provide new rules for guarding against such problems, was released for trial use by the ITER designers. To account for irradiation effects under monotonic loading, the ISDC contains several new rules which provide primary and secondary stress limits as functions of uniform elongation and ductility. These new rules were derived from a simple model based on the concept of an elastic follow up factor which has been used extensively by the Japanese and French designers for analyzing creep-fatigue problems in fission reactors. Detailed analytical and finite-element analyses were conducted and the results were compared with available test data to determine the limitation of the rules as they relate to the loss of a material's ductility and strain hardening capability.