Type of presentation: Poster

MS-14-P-5900 NanoSIMS and TEM analysis of deuterated ZIRLO and Zr-1%Nb nuclear fuel cladding alloys

Aarholt T. M.¹, Moore K. L.¹, Frankel P.², Preuss M.², Lozano-Perez S.¹, Grovenor C. R.¹

¹Department of Materials, Oxford University, Parks Road, Oxford, UK, ²Materials Performance Centre, School of Materials, University of Manchester, Manchester, UK

thomas.aarholt@materials.ox.ac.uk

NanoSIMS (Secondary Ion Mass Spectrometry), SEM (Secondary Electron Microscopy) and TEM (Transmission Electron Microscopy) have been used to study the hydrogen pickup of ZIRLO, a commercial zirconium alloy currently employed in the cladding material in nuclear reactors and Zr-1%Nb, a binary research alloy with particularly strong corrosion resistance. Samples were oxidised in autoclave in water for 80 and 180 and 540 days at 360°C to produce different levels of oxidation, two samples of each at pre- and post-transition. Further oxidation in 5% deuterium-rich water for 45 days at 350°C introduced deuterium to the metal and oxide, simulating the transit of hydrogen through oxidised samples in wet corrosion at the given moment of transition. The alloys were analysed in cross sections using NanoSIMS. Deuterium was found to distribute differently across the oxide in samples that experienced different oxidation times, with an interesting correlation to the breakaway behaviour of these oxides. In particular, peaks of deuterium concentration where found in the first micron of oxide. Large zirconium hydrides (deuterides) were found in the metal. SEM with Energy-Dispersive X-ray Spectroscopy (EDS) was used to relate the effect of second-phase particles to the distribution of deuterium in the areas analysed by NanoSIMS. Second phase particles containing Fe and Nb were found. TEM foils made by DualBeam Focussed Ion Beam allowed for microstructural comparison of the two alloys at pre and post-transition.

I would like to thank Westinghouse for funding this research.

Fig. 1: Cross section of post-transition Zr-1%Nb after 540 days oxidation in water and an additional 45 days in deuterated water, showing a slice through the oxide into the metal. NanoSIMS analysis shows large accumulation of deuterium in the oxide as well as a large deuteride (ZrH) in the metal.

Fig. 2: Line profile comparing the deuterium signal (red) with the oxygen signal (blue) from a cross-section of ZIRLO (deuterium image shown on the lower right) after 180 days oxidation in water and an additional 45 days in deuterated water. A peak in deuterium within the first micron of oxide is found to be consistent throughout measurements.