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SIMS21, Poland 2017 - Christopher Jones abstract

Christopher Jones oral presentation (SN1-Mon1-3-1)

Investigating hydrogen segregation during the corrosion of zirconium using NanoSIMS

Christopher Jones1, Greg McMahon1, Mhairi Gass2, Kexue Li3, Chris Grovenor3, Katie Moore1, Michael Preuss1

1 University of Manchester, Oxford road, M13 9PL Manchester, United Kingdom
2 Amec Foster Wheeler, 305 Bridgewater Place, WA3 6XF Warrington, United Kingdom
3 Oxford University, Parks Road, OX1 3PH Oxford, United Kingdom

Zirconium alloys are widely used for fuel cladding in light water reactors. While in service they encounter high temperature, aqueous environments and thus undergo oxidation. During the corrosion process, hydrogen is taken up by the zirconium and its concentration in the metal is a limiting safety factor in the lifetime of fuel cladding [1]. As such it is vital to understand the behavior of hydrogen during corrosion.

Spatial localisation of hydrogen at the scale of the microstructure has proven difficult with conventional methods. However high-resolution secondary ion mass spectrometry is one of the few techniques able to image hydrogen in metals with sub-micron resolution [2]. The difficulty in detecting hydrogen with SIMS is that it is difficult to distinguish between hydrogen that entered the material during service and hydrogen absorption on the sample surface from residual gases in the vacuum system. Spiking the solution with deuterium during the corrosion process solves this problem as its natural concentration is negligibly low.

Two Zircaloy-4 samples were corroded in a deuterium spiked aqueous environment before being examined in cross section using the Cameca NanoSIMS 50L at the University of Manchester and the NanoSIMS 50 at the University of Oxford. When examined, deuterium was found to segregate to sites in the metal substrate. These sites have been found to largely correlate to small regions producing high FeO-, CrO- and NiO- signals.

As Zircaloys typically contain two different types of single phase particles (SPPs), Zr(Fe,Cr)2 and Zr2(Fe, Ni), the results suggest that the SPPs possibly play a role during corrosion as a potential hydrogen sink. However, as the apparent segregation is more pronounced in the upper layers of the SIMS analysis, it is necessary to consider the role of surface effects and potential contamination and this is a focus of current work.

Further correlation is also currently underway using scanning electron microscopy in conjunction with low voltage EDX analysis to confirm the presence of SPPs where deuterium enrichments were found.

[1] S. Sobieszczyk, “Hydrogen-enhanced degradation and oxide effects in zirconium alloys for nuclear applications,” Int. J. Hydrogen Energy, vol. 6, no. 36, pp. 8619–8629, 2011.

[2] S. S. Yardley, K. L. Moore, N. Ni, J. F. Wei, S. Lyon, M. Preuss, S. Lozano-Perez, and C. R. M. Grovenor, “An investigation of the oxidation behaviour of zirconium alloys using isotopic tracers and high resolution SIMS,” J. Nucl. Mater., vol. 443, no. 1–3, pp. 436–443, 2013.