Assessment of radiation effects relating to reactor pressure vessel cladding

Because the weld overlay cladding on the interior of light-water reactor pressure vessels was applied for corrosion resistance and not for structure, little attention has been given to the potential of mechanical property degradation due to radiation exposure. In light of the concerns recently raised regarding overcooling transients in nuclear power reactors, it has been suggested that any such degradation could adversely affect the serviceability and/or integrity of the vessel. A literature survey assesses the current knowledge regarding the effects of neutron radiation on the mechanical and fracture properties of stainless steel weld overlay cladding under conditions relevant to light-water reactor operation. In particular, effects on the material's microstructure and tensile, fatigue, impact, and fracture properties are examined. Although information is lacking on the specific materials under the exact irradiation conditions of interest, a wealth of information is available on irradiated stainless steel weldments in general, from which basic behavioral trends can be obtained. Some irradiation embrittlement apparently does occur in stainless steel weldments at the relatively low temperatures and fluences typical of light-water reactors. Tensile strength increases and ductility decreases. Low-cycle fatigue behavior is degraded somewhat, but high-cycle fatigue and fatigue crack growth seem largely unaffected. Effects of delta-ferrite on fracture resistance are small in both irradiated and unirradiated materials. Notch impact and fracture toughness are both reduced by irradiation, and a dependence of toughness on testing rate, not seen in wrought material, is indicated