UN is a promising accident tolerant fuel (ATF) concept with numerous benefits over conventional UO₂ fuel, such as increased uranium density and thermal conductivity with a similar melting point [1]. Thus, understanding its stability under extreme conditions in a high temperature steam and radiation environment becomes critically important. The current work will discuss the radiation response of coarse-grained ZrN fabricated using spark plasma sintering and magnetron sputtered monocrystalline UN thin films. 600 keV Ar ion irradiations were carried out to understand material modifications by primary knock-on atoms (PKAs) from neutrons and gas accumulation as a function of damage dose from 1 dpa – 100 dpa. As ZrN is isostructural to UN, it is used as its model material [2], while the thin film configuration of UN presents a unique opportunity to study its radiation response due to its negligible activity and therefore ease of handling during characterisation. The irradiated samples were characterised by x-ray diffraction, transmission electron microscopy and Raman spectroscopy. Nanoindentation is used to understand corresponding changes in hardness and modulus. Throughout its operational lifetime, UN and ZrN will experience harsh reactor environments. Accordingly, observed microstructural modifications are correlated with physical property changes with relevance to nuclear fuels. Results have shown that the chemical composition and lattice parameter of ZrN is minimally perturbed at all fluences, while crystallinity displays a significant increase of ~50% in the irradiated region. Pronounced hardness and modulus increases are observed post-irradiation. Cross-sectional TEM and SAED observations revealed the radiation-induced formation of an epitaxially matched surface layer of cubic ZrO₂ to the underlying bulk ZrN. Furthermore, evidence of a correlated disorder and commensurate ordering is displayed through selected area electron diffraction analysis of irradiated ZrN regions. These results will assist in our understanding of fuel degradation over its lifetime and shed light on the effects of PKAs in nuclear fuel, as well as the accumulation and diffusion of gas bubbles due to fission processes. Alongside this project, we are investigating the effects of 600 keV Ar and higher energy ion irradiations of 1.5 MeV Si, 9 MeV Si and 7 MeV Au in nanocrystalline IBAD ZrN films. Nanocrystalline materials hold promise for possessing increased radiation tolerance owing to its high density of large angle grain boundaries [3,4]. This work primarily explores the distinct effects of ionising and displacive interactions and target material grain size. References [1] Yun, D. et al. Materials Reports: Energy 1 (2021) pp. 100007. [2] Wheeler, K. et al. Journal of Nuclear Materials 366(3) (2007) pp. 306–316. [3] Zhang, Y. et al. (2014) Physical Chemistry Chemical Physics, 16(17), pp. 8051–8059. [4] Lu, F. et al. (2012) Applied Physics Letters, 101(4).