Kmc Modeling of Helium

The effect of helium in iron is an important issue in nuclear systems, as iron and iron alloys (steels) are the primary materials used for structural elements. Helium is known to cause embrittlement and decrease fatigue life, as well as aid creep and promote swelling. These effects can significantly alter the mechanical properties of the reactor materials, and generally lead to early failure and decreased part lifetimes. This is a concern in both fission and fusion systems. The precise role that helium, helium-vacancy clusters, and helium bubbles play in the material degradation processes described above are still only partially understood. Further understanding into the role helium plays in these phenomena is essential to predicting the lifetime of iron and steels in nuclear reactors. This work was motivated by the results found earlier by Okuniewski. Said work was primarily experimental work studying the effects of helium concentration on cluster size distribution. KMC simulations were run for comparison, but the results were inconsistent. Both with and without helium present, the results showed the KMC simulation resulted in a significant shift compared to the experimental results. The KMC simulations predicted a high density of small sized clusters, while the experimental results showed a lower density of larger sized clusters. This inconsistency was believed to be a result of the various parameters chosen in the KMC model. This work focused on two primary goals: first, to develop a flexible KMC code capable of simulating the desired models, and second, to explore the modeling assumptions made in the previous KMC simulations in an attempt to come closer to experimental results. Several different models for cluster interaction range, dissociation energy, and migration energy were considered, and a KMC code was designed and built to accommodate these and other models. The code design will be presented, along with performance benchmarking results. Both annealing and damage simulations were then performed with varying combinations of parameter models. The results of these simulations are compared and discussed.