Effect of fast neutron irradiation and helium injection on the mechanical properties of austenitic stainless steel

Austenitic stainless steel is a candidate material for the fuel cladding and other core components in the fast breeder reactor. For reactor design and safety analysis it is necessary to define the effects of neutron irradiation on the high temperature mechanical properties of the alloys. It is well established that fast reactor irradiation greatly reduces ductility of austenitic stainless steels. Ductility loss increases monotonically with neutron fluences in both tensile and creep-rupture test. Embrittlement of stainless steel irradiated at below 5500C is due to plastic instability while for the specimen irradiated at above 6500C embrittlement is due to helium produced by transmutation of constituents. The loss of ductility caused in the intermediate temperature range is believed due to both mechanisms. The paper presents the results of a study on mechanical properties of Type 316 stainless steel tube which was irradiated in the Dounreay Fast Reactor at temperature between 250 and 5000C and to fast neutron fluence of 2.0 to 7.8 x 1022 n/cm2 (E > 0.1 MeV). The effects of helium injection on the creep rupture properties of Type 316 stainless steel with minor constitution variations as well as the effects of titanium modification on the tensile properties of irradiated Fe - 17Cr - 13Ni base alloys are also presented