Dr Lottie Harding - University of Bristol

The challenge

A programme is underway in the UK to accelerate the qualification of new nuclear technologies to increase nuclear power generation by 2050 as part of net ero ambitions. The reactor of choice is a high-temperature gas-cooled reactor (HTGR), which uses a novel nuclear fuel called TRi-structural ISOtropic (TRISO) fuel. The TRISO concept encapsulates uranium-containing fuel kernels in a series of carbon and ceramic layers. For the practical implementation of HTGRs to be realised, the TRISO concept must be developed beyond the current state of understanding. Key to this is the chemical, structural and thermal properties of the fuel.

The research

Led by Dr Lottie Harding, project BUTTER will address these challenges, enhance the UK’s capability in nuclear fuel engineering using novel thin film approaches, and support net zero ambitions. 

Several uranium-based phases are proposed as the fuel kernel for the TRISO concept including the traditional uranium dioxide (UO2) phase and the advanced uranium mononitride (UN) system. A major complication of these binary systems is that bulk TRISO fabrication results in the formation of ternary phases, mixtures of uranium-carbon-oxygen (UCO) and uranium-carbon-nitrogen (UCN), which are unavoidable and poorly understood. It is imperative that these ternaries are fully understood for TRISO-fuelled technologies to be introduced into the nuclear fuel cycle. Project BUTTER will enhance our understanding of these TRISO ternaries from fabrication to long-term storage. Through engineering novel TRISO ternary surfaces, Dr Harding will rapidly explore the structural, chemical, and thermal behaviour of each ternary phase, accelerating the qualification of TRISO for next-generation fission rectors.

The researcher

Dr Lottie Harding is the research lead at the University of Bristol for the Sellafield Uranium and Reactive Metals Centre of Expertise, and for investigating advanced fuel technologies in collaboration with the United Kingdom National Nuclear Laboratory. These concurrent roles have allowed her to adapt her expertise in surface-based fabrication and analytical methods to understand a wide range of nuclear fuel types relevant to legacy, current, and future nuclear fuel cycles – leading to the creation of project BUTTER. Her expertise in phase-diagram exploration via surface engineering will help accelerate the qualification of TRISO fuels into next-generation fission reactors.