Simultaneous Corrosion/Irradiation Testing in Lead and Lead-Bismuth Eutectic: The Radiation Decelerated Corrosion Hypothesis (RC-3)

Nuclear fission power plays a vital role in supplying the UK with low carbon footprint electricity. 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, ~20% of total UK electricity, will need to be provided by other sources, e.g. fossil fuel power stations. This would be detrimental to UK greenhouse gas emissions and contribution to climate change. For successful decarbonisation by the 2050s, UK new build of future fission reactors is urgently needed.

Liquid lead (Pb) and lead-bismuth eutectic (LBE) cooled fast reactors promise the best power density and economics among fission reactors. However, for decades now the development of these reactors has been stuck because of concerns about the combined effect of Pb/LBE corrosion and irradiation on the structural materials they would use. Moreover, the problem is that to actually test how bad the corrosion is, one would either have to setup an experiment in an existing research reactor or indeed build a whole new Pb or LBE-cooled research reactor. This would be prohibitively costly, slow and it would be challenging to build and license a test reactor without initial understanding and prediction of material performance. A much faster way of studying combined irradiation and corrosion of materials for Pb/LBE cooled fast reactors is needed!

Here we address this problem: Our project partners at MIT, USA, have developed 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. Whilst protons don't perfectly mimic the damage caused by neutrons, they capture the key mechanisms well. Most importantly these experiments are much quicker and cheaper than e.g. 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.

After exposure, the Oxford partners of the project team will then analyse the samples to determine how Pb/LBE corrosion proceeds in the presence of irradiation, and how this differs from Pb/LBE corrosion without irradiation. Curiously our initial results show that irradiation slows down the rate of corrosion! To explore and understand this behaviour, we will perform characterisation of the structure and chemical composition of samples after exposure, from the macroscopic down to the atomic scale. This microstructural characterisation will be combined with mechanical testing of the exposed materials carried out by US project partners at the North Carolina State University.

Overall the results from this project will finally address how simultaneous irradiation modifies the corrosion behaviour of alloys for Pb/LBE cooled fast reactors. It will allow us to identify which of the tested candidate alloys performs best and what the key mechanisms are that control its degradation during combined corrosion and irradiation. This information is vital for overcoming the current stagnation of progress in the development of Pb/LBE cooled fast reactors, and to allow directed optimisation of the structural and cladding materials they require.

Academic benefits:
This project will provide a unique, proof-of-concept facility for combined corrosion and irradiation testing. Looking ahead this facility will provide a key capability for rapid, high throughput quantification of combined corrosion and irradiation performance of reactor materials. Importantly this is not limited to Pb/LBE corrosion, but based on lessons learnt from this facility, researchers could further develop this capability to investigate the combined effect of other, reactor-relevant, corrosive environments and simultaneous irradiation. This will dramatically speed up the process of materials discovery for reactor applications, which is currently progressing at a glacial pace, largely due to a lack of insitu testing capabilities that allow cost efficient, rapid quantification of materials performance under reactor-relevant conditions.

The experimental data produced in this project will uniquely explore the combined effect of Pb/LBE corrosion on structural alloys for LFR/LBEFR reactors. By characterising sample composition and structure from the atomic to the macroscopic scale, we will clarify which mechanisms control material degradation under corrosion and simultaneous corrosion & irradiation. This is vital information for the directed development of corrosion and irradiation resistant alloys, where the microstructure is engineered to optimise longevity. In particular, detailed data about the about local material structure and composition at corrosion sites, e.g. grain boundaries, will be key for the development of multi-scale materials models of the combined irradiation and corrosion process.

Economic benefits:
Mechanistic insight into the degradation of different alloys due to combined LBE corrosion and irradiation is the main advance required for LFR/LBEFR test reactor development, licensing, and ultimately commercialisation of the technology. In this project we will develop a world leading activity in this area, gaining much needed insight into the performance of current best-in-class alloys. Experience gained in rapid testing of alloys under reactor-relevant conditions and the subsequent multi-scale analysis to determine underlying mechanisms will be directly fed forward to UK nuclear industry through our strong network of industrial partners. Licensing is a further key aspect of new reactor development. This project potentially provides a whole new set of tools that could be used by the UK regulator to assess the performance and safety of key materials systems for advanced reactor concepts. Together, this will place the UK in a very strong international position for advancing the development and commercialisation of lead/LBE cooled fast reactor technology.

Societal benefits:
In the short and medium term, before long-term, fully sustainable energy sources such as nuclear fusion become available, nuclear fission power provides an attractive, low carbon footprint source of electricity. Among nuclear fission reactors LFRs and LBEFRs promise the best power density and economics. However, for decades their development has been hindered by concerns about the combined effect of corrosion and irradiation. This project directly addresses this major bottleneck, brining key new experimental approaches and much needed data to the table. As such it will hasten LFR/LBEFR deployment, and decarburisation of electricity provision both in the UK and worldwide.