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Christopher Nellis

Publications and source records attributed to Christopher Nellis.

2 recordsLinked to original sources
arXiv2022

Kinetic Monte Carlo modelling of Helium Bubble Nucleation onto Oxides in the Fe-Ti-Y-O System

A Kinetic Monte Carlo (KMC) model was created to simulate the insertion of transmutation He atoms into nanostructured ferritic alloys (NFAs) under neutron irradiation. Interstitial He atoms migrate through the NFA until becoming trapped in bubbles of other He atoms and vacancies created from irradiation. The Y-Ti-O nano-oxides in the NFAs were found to be effective in capturing these He atoms and preventing bubbles from forming at the grain boundary and appear to replicate the characteristics (size and number density) observed in other experiments. The bubbles were found to prefer the <111> oxide interface as a nucleation site and the stable bubbles have a He/Vac ratio between 1.3 and 1.8 He/Vac. The influence of He bubbles on the segregation of solutes to the grain boundaries or on the stability of the nano-oxides were negligible.

cond-mat.mtrl-sci↗
arXiv2022

Kinetic Monte Carlo Modelling of Nano-oxide Precipitation and its Associated Stability under Neutron Irradiation for the Fe-Ti-Y-O system

While developing nuclear materials, predicting their behavior under long-term irradiation regimes spanning decades poses a significant challenge. We developed a novel Kinetic Monte Carlo (KMC) model to explore the precipitation behavior of Y-Ti-O oxides along grain boundaries within nanostructured ferritic alloys (NFA). This model also assessed the response of the oxides to neutron irradiation, even up simulated radiation damage levels in the desired long dpa range for reactor components. Our simulations investigated how temperature and grain boundary sinks influenced the oxide characteristics of a 12YWT-like alloy during heat treatments at 1023 K, 1123 K, and 1223 K. The oxide characteristics observed in our simulations were in good agreement with existing literature. Furthermore, the impact of grain boundaries on precipitation was found to be minimal. The resulting oxide configurations and positions were used in subsequent simulations that exposed them to simulated neutron irradiation to a total accumulated dose of 8 dpa at three temperatures: 673 K, 773 K, and 873 K, and at dose rates of 10^(-3), 10^(-4), and 10^(-5) dpa/s. This demonstrated the expected inverse relationship between oxide size and dose rate. In a long-term irradiation simulation at 873 K and 10^(-3) dpa/s was taken out to 66 dpa and found the oxides in the vicinity of the grain boundary were more susceptible to dissolution. Additionally, we conducted irradiation simulations of a 14YWT-like alloy to reproduce findings from neutron irradiation experiments. The larger oxides in the 14YWT-like alloy did not dissolve and displayed stability similar to the experimental results.

cond-mat.mtrl-sci↗