Fundamental Studies into Uranium Diboride and Uranium Mononitride for use as Advanced Technology Fuels in Light Water Reactors

Abstract

Since the early 1950’s, Nuclear Power has developed as a key source of civilian electricity. Following a few historical incidents involving nuclear power, steps have been taken to investigate ways in which nuclear power can be made safer, with the most prevalent options seeking changes in existing safety controls. Researchers have highlighted an area of focus, with investigations being launched into the fuel-cladding systems used. Currently, UO2 is the fuel used in Light Water Reactors (LWRs), but a new class of ceramic-based fuel materials called Accident Tolerant Fuels (ATFs) have gained traction in recent literature. In a two-part study preliminary to composite testing, two samples of candidates for Accident Tolerant Fuels (ATFs) were analysed to better understand fundamental aspects of their behaviour. Firstly, sintered pellets of UB2 were analysed using Raman Spectroscopy. This highlighted key similarities between other well-studied borides and graphene and enabled the identification of UB2 through Raman Spectroscopy for the first time. It was determined, through the application of Group Theory and Raman Spectroscopy, that UB2 is structured similarly to graphene, with boron existing in honeycomb-like sheets, providing potentially improved robustness when compared to existing fuel materials. Secondly, Uranium Mononitride (UN) was synthesised and tested in highly oxidative conditions. UN has garnered attention in the nuclear industry as an ATF due to its high thermal conductivity and uranium density, but concerns regarding resilience to high-temperature steam and oxidative conditions has slowed research. Therefore, to address concerns over poor oxidation resistance, UN was synthesised using the hydride-nitride-denitride (HDN) route and tested in synthetic air using Thermogravimetric Analysis (TGA) to better understand general degradation with time and storage conditions. After 50 days, it was determined that, through TGA and powder X-Ray Diffraction (XRD), the forced oxidation proceeded as expected, with little change between samples over the course of the 50-day period, regardless of storage conditions. This multifaceted study aims to enhance field understanding of both UB2 and UN as individual materials, with the aim to lay the groundwork for future composite studies.

Date of Award	31 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Joel Turner (Supervisor) & Timothy Abram (Supervisor)