Understanding UN Nuclear Fuel

: A Study of the Fundamental Physical Behaviour and Degradation of Uranium Nitrides

Abstract

Improvements in safety and economic performance are sought for the future of the commercial nuclear power industry and can partly be provided by an improved fuel. Uranium mononitride, UN, offers higher thermal conductivity and uranium density compared to the widely used UO2, however, understanding of the fundamental and applied behaviour of UN must be improved if it is to be used as a nuclear fuel. Thin films provide highly versatile, idealised samples that are well suited for investigations into such properties. Epitaxial UN and U2N3 thin films have been grown for the first time using reactive DC magnetron sputter deposition, enabling new measurements of the intrinsic properties of these materials. Characterising these samples, x-ray photoelectron spectroscopy and anisotropic resonant scattering performed at the M4 edge for first time show the mixed bonding present in U2N3, highlighting the differences between UN and U2N3. Resonant scattering measurements also provide insight into the antiferromagnetic ordering of both UN and U2N3. Thin films also provide ideal samples for surface investigations, facilitating a highly controlled approach to researching the degradation of UN. A study of UN oxidation shows that a passivating oxide layer forms and a U2N3
interlayer is present even during room temperature oxidation. The effect of radiation on corrosion is also considered, with investigations comparing the effect of exposure to H2O2, mimicking radiolytic products, on UN, U2N3, and
UO2. The relative corrosion resistance of UN shows that this is an area of research that needs further consideration. Finally, the implications of these results for the fundamental understanding of UN and its application as a nuclear fuel are considered.

Date of Award	28 Nov 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ross S Springell (Supervisor)