During operation, deuterium-tritium fusion devices generate high-energy neutrons that penetrate the lattice of reactor components, triggering collision cascades. The resulting material defects cause degradation of the thermal and mechanical properties of the constituent material. Nanocrystalline materials, characterised by their small grain size, have been proposed for reactor applications due to their high grain boundary density. Grain boundaries are thought to act as sinks for irradiation defects, increasing the lifespan of reactor materials. FeCr binary alloys can be studied as model materials to understand the behaviour of reduced activation ferritic–martensitic steels likely to be used in the first wall and breeding blanket of future fusion reactors. In this poster, we present the results of our irradiation simulations on ARCHER2 and make comparisons with experimental data. LAMMPS is used to run collision cascade simulations, mimicking irradiation damage in nanocrystalline Fe and FeCr. For comparison, initially pristine cells are also irradiated. ARCHER2 was vital for these simulations as it allowed for large cell sizes that capture collective physical effects whilst also enabling large dose simulations to explore long-term evolution. Grain growth is observed for all nanocrystalline cells, and a lower final dislocation density for initially nanocrystalline cells when compared to pristine cells. Chromium does not appear to alter the grain growth rate. Remarkably the growth rate from MD simulations, closely matches that observed in XRD measurements of ion-irradiated, nanocrystalline Fe and FeCr discs.These results reveal key mechanisms underlying nanocrystalline material evolution under irradiation, providing guidance for developing next-generation radiation-resistant steels.