| dc.description.abstract | In the nuclear reactor core, materials perform under harsh operating environments, including high temperature, high stress, and severe radiation damage. These conditions weaken the operational performance of the material. Radiation-induced segregation (RIS) is one of the primary material degradation problems in nuclear reactors. Irradiation creates excess vacancy and interstitial point defects in alloys. These point defects can be canceled by mutual recombination or annihilation of defects at grain boundaries, surfaces, or dislocations. Consequently, irradiation gives rise to point defect fluxes toward the sinks, leading to enrichment or depletion of alloying elements at defect sinks. For Ni-Cr alloys, the depletion of Cr at grain boundaries can cause irradiation-assisted stress corrosion cracking (IASCC). This is one of the problems associated with RIS. Thus, a quantitative understanding of RIS is crucial for the design and development of nuclear materials. To better understand RIS in Ni–Cr alloys, the rate theory approach is employed.
The balance equations for point defects and alloy atoms were solved simultaneously using a fully-coupled and fully-implicit scheme implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework, considering the combined effects of dose rate, temperature, grain size, sink density, and production bias. Simulations have been conducted and compared with the experimental data. We demonstrate a strong dependence of RIS on size, production bias, and temperature. It was shown that the magnitude of enrichment/depletion of Ni/Cr at the boundary increases with size, and the width of the enrichment/depletion layer also increases with size. As the temperature decreases, RIS becomes more apparent with higher segregation of Ni and depletion of Cr at the boundary as the production bias increases. It is also noteworthy to the point that RIS shows dependency on the irradiation type and conditions. Adding different sink density tend to alter the width of the enrichment/depletion layer of RIS. Moreover, when surface and size effects are considered, qualitative differences in the irradiation response of materials to different irradiation types are expected. Here, we proved that, in addition to its known dependence on material and size/microstructure, the surface/boundary sink strength is dependent on irradiation type. | en |
