Solution-annealed austenitic stainless steel Type 316L has been selected for use in the next European torus first wall, where it will be subjected to simultaneous thermomechanical loading and irradiation damage. In this context, specimens taken from the European reference type 316L steel and welds, including electron beam, manual metal arc, and weld deposits, have been irradiated at temperatures between 412 to 545°C to neutron doses ranging from 15 through 41 dpa. Postirradiation experiments conducted have included density and dimensional measurements, tension, fracture mechanics, fatigue crack growth rate, low-cycle fatigue, and creep-fatigue tests, in both irradiated and control conditions.
It has been found that irradiated specimens undergo dimensional changes, with a maximum swelling (about 5%) occurring in specimens irradiated to 41 dpa at about 450°C. Yield stress and ultimate tensile strength have been found to sharply increase, reaching levels as high as 250% in the temperature range of 400 to 450°C. Concurrently, a significant decrease has been observed in the tensile elongation, with the uniform elongation of some welded specimens attaining values as low as 1%. Fracture toughness of welded materials has also been found to sharply decrease, particularly in weld deposits. Fatigue crack growth rate and continuous fatigue resistance of weldments have been found to be particularly affected by irradiation.
The above findings are analyzed, and several design criteria are tentatively proposed for austenitic stainless steels used in structures exposed to irradiation doses ranging from 15 to 41 dpa. It is concluded that for NET conditions, where the irradiation doses are significantly lower than the doses used in the present study ( < 15 dpa), the mechanical property changes will be less severe and the swelling less significant.