Performance of Uranium Nitride as an Advanced Technology Fuel for use in Light Water Reactors

Abstract

This thesis explores the potential of uranium nitride (UN) as a fuel for light water reactors. UN has a high uranium density and thermal conductivity. However, its adoption is hindered by its susceptibility to oxidation in high-temperature steam and its largely unexplored compatibility with cladding materials. The research addresses key challenges associated with UN, including its steam tolerance, high-temperature air oxidation resistance, and interactions with Zircaloy-4 and silicon carbide (SiC) claddings. The effects of niobium (Nb) incorporation on the oxidation behaviour of UN was also examined to assess its viability as an advanced technology fuel. Experimental investigations included oxidation tests in high-temperature steam and synthetic air, as well as diffusion couple experiments. Experimental investigations revealed that the age and storage environment of UN powder - whether in air or water vapour - had minimal influence on its oxidation behaviour up to 900 °C after 129 days of storage. The incorporation of niobium into UN via spark plasma sintering (SPS) demonstrated slower oxidation kinetics during high-temperature steam exposure but did not alter the oxidation onset temperature. Diffusion couple experiments revealed that UN exhibited minimal interaction with Zr-4 at in-reactor temperatures (~400°C). However, above 1000 °C, significant uranium migration into the cladding (>600 µm) was observed, coinciding with the β-phase transition of Zr-4. In contrast, minimal interaction was observed between UN and SiC at 1000 °C.

Date of Award	9 Jun 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Joel Turner (Co Supervisor), James Buckley (Co Supervisor) & Timothy Abram (Main Supervisor)