Confirming Oxford University as one of the key UK players in nuclear energy materials R&D, Associate Professor Felix Hofmann (Department of Engineering Science), and Associate Professor David Armstrong (Department of Materials) have both been awarded prestigious EPSRC grants to work with US partners on materials for the next generation of nuclear fission reactors.
The grants are worth approximately £1m in total, with a similar funding contribution from the US-based Nuclear Engineering University Partnership program (NEUP).
"For successful decarbonisation by the 2050s, new build of future fission reactors in the UK is urgently needed"
Nuclear fission power plays a vital role in providing the UK with low carbon footprint electricity, generating ~20% of the total UK electricity supply. The current UK fleet of nuclear reactors is rapidly ageing, and all of these reactors are scheduled to be removed from service within the next 12 years. Without replacement, the electricity they generate would need to be provided by other sources, such as fossil fuel power stations.
Professor Hofmann says, “Moving to fossil fuels would be detrimental to UK greenhouse gas emissions and make a significant contribution to climate change. For successful decarbonisation by the 2050s, new build of future fission reactors in the UK is urgently needed.”
Two reactor types have been proposed that have the potential to offer dramatically improved efficiency over current water-cooled reactors: Liquid lead (Pb) and lead-bismuth eutectic (LBE) cooled fast reactors, or molten salt cooled reactors. However, for decades now the development of these reactors has been at a standstill because of concerns about the corrosion these high temperature liquid coolants would cause in the structural materials used. These Oxford led grants both aim to accelerate the understanding of the specific corrosion mechanisms, which are very different to those in more common water cooled reactors and develop new materials to operate in these extreme conditions.
The project, led by Professor Hofmann, together with US lead Professor Michael Short, MIT, and colleagues at North Carolina State University, concentrates in particular on investigating the combined effect of Pb/LBE exposure and irradiation on structural steels. Previously, to test how significant the corrosion could be, experiments on a specialised research reactor would have been required to scope-out candidate material systems - a prohibitively costly, slow and challenging process.
"A much faster way of studying combined irradiation and corrosion of materials for Pb/LBE cooled fast reactors is needed. This grant will allow us to address this"
Professor Hofmann explains, “A much faster way of studying combined irradiation and corrosion of materials for Pb/LBE cooled fast reactors is needed. This grant will allow us to address this. Working with project partners at MIT in the USA, we will use a new, one-of-a-kind facility that allows the simultaneous exposure of materials to Pb/LBE corrosion and insitu irradiation with protons. The protons are used to mimic the effect of neutrons in a fission reactor.”
He adds, “These experiments are much quicker and cheaper than in-reactor material testing. Using this new tool, we will explore the performance of five of the current front-runner alloys for cladding and structural components in Pb/LBE fast reactors. We will also compare the results against more traditional Pb/LBE corrosion tests to make sure the new combined irradiation and corrosion facility performs as anticipated.”
Professor Armstrong’s project concentrates on investigating new alloy systems that can better resist the extremely corrosive environment in molten salt cooled reactors. He explains, “Molten salts make excellent coolants due to a higher volumetric heat capacity than pressurized water. However, molten salt is corrosive and will attack and essentially dissolve some materials, including many common grades of stainless steel. If these reactors are to be used commercially then new grades of nickel alloys that do not suffer such corrosive attack in contact with the salt are urgently needed.”
The results from these projects will address some of the key material challenges for the successful development of Pb/LBE or molten salt cooled reactors
Addressing this need is at the core of this project. Professor Armstrong describes: “Previous grades of nickel alloy became brittle when exposed to irradiation in a reactor, because of the helium produced in the process. In this project, in collaboration with Idaho National Laboratory, North Carolina State University and University of California, Berkeley in the USA we will design, develop and process new nickel alloys that contain tiny oxide particles that effectively trap helium and stop it causing premature failure. We also hope that these particles will make these alloys stronger at high temperatures, allowing more efficient reactor operation.”
The results from these projects will address some of the key material challenges for the successful development of Pb/LBE or molten salt cooled reactors. They will enable the researchers to identify which of the tested materials perform best and what the key mechanisms are that control material degradation. This information is vital for overcoming the current stagnation of progress in the development of next generation Pb/LBE or molten salt cooled reactors, and will allow directed optimisation of the structural and cladding materials they require.