As Professor of Materials in Oxford University, I am responsible for the NanoAnalysis group (see all current members here: People). Our Research makes use of state-of-the-art facilities, characterization techniques and novel data analysis routines to push our understanding of materials properties through high-resolution characterization. We have worked in the area of environmental degradation of nuclear reactors for over 20 years, with an excellent track record. Our work is internationally recognized for initiating the NanoSIMS, atom-probe and electron microscopy characterization of radiation damage, environmental cracking and surface oxidation at the highest levels of resolution. Current projects on nuclear materials are in collaboration with EDF, INSS, CNL or Westinghouse. I have published more than 150 papers (see Publications) and currently hold several EPRSC and industrial grants
Characterisation of deuterium distributions in corroded zirconium alloys using high-resolution SIMS imaging
Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup (HPU) which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at second phase particles in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.
Microstructural understanding of the oxidation of an austenitic stainless steel in high-temperature steam through advanced characterization