DETERMINATION OF IRRADIATED STAINLESS STEEL PROPERTIES AND ITS EFFECTS ON REACTOR VESSEL INTERNALS

Reactor vessel internals (RVIs) consist of austenitic stainless steels (ASSs) which have excellent material properties. Meanwhile, the high radiation environment of a reactor can cause the degradation of components. Since changed material properties are important for long-term operation, experimental researches related to tensile and fracture properties had been conducted. However, it is limited to investigate these researches due to their high radioactivity and small quantity. Thus recent researches have been dedicated to small specimens such as nanoindentation and micropillar compression tests and so on with ion-irradiation. In this study, micropillar compression tests were carried out for virgin and irradiated 304 ASSs to obtain microscopic mechanical behaviors. The trial sets of finite element (FE) analyses were performed to derive dislocation density based material constitutive equations for austenite phase by comparing with test results. Subsequently, representative volume elements analyses with periodic boundary conditions were adopted to estimate overall tensile stress-strain curves as well as 0.2% offset yield strengths (YSs) under the virgin and irradiated states. Finally, the effect of irradiated properties on typical RVIs were investigated. As typical results, optimized material parameters related to dislocation density based formulations were revealed, and microscopic stress-strain curves were reasonably comparable with test results. The estimated YS values were compared with the experimental results and corresponded within 9.09%. The overall deformation, stress and strain behaviors of typical RVIs were examined considering estimated properties, of which details and key findings will be discussed.