Materials properties of irradiated austenitic stainless steel for LWR internal applications

The internal structures of LWRs are highly neutron-irradiated due to the close presence of the reactor core. Dose levels in the range of 10 to 80 dpa are reached at certain locations of the internal components at end-of-life conditions. The austenitic stainless steel structural material of the internal components including the weld metals suffer from the neutron irradiation resulting in strong radiation hardening, loss of ductility, and degradation of fracture toughness. The integrity of the internal structural components is an important aspect in the safe operation of the LWRs. This paper presents information on the mechanical properties after test reactor irradiations of Type 316L(N) and Type 304L austenitic stainless steel plate materials and 1668-2SP TIG deposit and Type deposit and Type 308L SAW weld material. The irradiation experiments have been performed in the High Flux reactor (HFR) at Petten in the temperature range of 250 deg C to 425 deg C and to damage dose levels up to 10 dpa. The tensile tests provide information on the dose dependence of irradiation hardening and loss of ductility. The unirradiated austenitic stainless steel exhibits extremely high fracture resistance (>1000 kJ/m2), but it is shown that the degradation of fracture toughness follows a general trend and seems to saturate in the dose range of 5 to 10 dpa. The presented information is discussed in relation to data from open literature and applicability to LWR internal applications. (authors)