Experimental studies of radiation damage in uranium nitride

Abstract: The effect of proton (H+) irradiation on uranium mononitride (UN) and UN compositefuel with 10 at.% ZrN (UN10at%ZrN) was examined. Protons of 2 MeV with fluences of1E17, 1E18, 1E19 and 1E20 ions/cm2 were accelerated towards the fabricated samples in orderto investigate the evolution of the micro-structure. Stopping and Range of Ions in Matter(SRIM) calculations were performed to determine the displacements per atom associatedwith the depth of the highest damage, for each fluence.X-Ray diffraction (XRD) was used in both samples to identify the chemical composition ofeach pellet, which revealed the low presence of oxygen. Based on scanning electron microscopy(SEM), deterioration of the samples surface was observed, as the proton fluence increased.The applied stress due to the irradiation, led to the cracking of the pellets at the highestfluences. Blisters and craters appear to surround the cracked region, which might originatefrom the significant levels of hydrogen implantation within the samples.From Electron backscatter diffraction (EBSD) analysis, the grain size of the UN10at%ZrNcomposite was found to be smaller than in UN, due to the nano-particle nature of the ZrNpowder. The latter technique was also used to observe the elevated irradiated regions, whichwere further investigated by atomic force microscopy (AFM). Nano-indentation detectedirradiation hardening for both samples in the irradiated regions. Focused ion beam (FIB)milling was applied to remove lamellas from the cracked regions in both UN and compositesamples in order to be analyzed by transmission electron microscopy (TEM). The latter mightreveals the formation of dislocation loops in the irradiated areas.