In Situ High-Pressure Diffraction Studies of UO2 with H2O and He/Ar/Xe to 20 GPa

The present proposal seeks to perform high resolution X-ray diffraction measurement of UO2 single crystals immersed in H2O media under reduced atmosphere conditions of He, Ar and Xe up to pressures of 20 GPa. Under intrinsic conditions UO2 is established to be stable as fluorite in space group Fm-3m until 40 GPa. However, we have recently demonstrated under oxidising conditions and when exposed to H¬2O, UO2 can transform to U3O7 at pressures as low as 6 GPa. The present proposal seeks to establish if such phenomena can occur under reducing conditions (He, Ar and Xe) and particularly those directly relevant to spent nuclear fuel (SNF) when stored in a geological repository. The proposed proposal is thereby relevant to both general actinide chemistry, high-pressure science in addition to SNF disposal practises. The experiment is intended to be performed using either the high-pressure beamlines ID15B or ID27, which are both perfectly equipped for such work to be successfully completed.