Speaker
Description
Zr alloys have been broadly used as cladding materials in fission reactors since 1950s [1, 2]. A universal degradation issue in this field is the oxidation of Zr cladding materials, which has been widely investigated in the past decades [3-5], but there is insufficient understanding of hydrogen ingress process during corrosion due to the fundamental difficulties in hydrogen detection. Atom probe topography (APT) has an equal and very high detection sensitivity to all elements [6], but contaminant H is readily and frequently incorporated during tip preparation using focussed ion beam (FIB) and from the adsorption of H2 from the analysis chamber metal walls. It is thus challenging to distinguish the contaminant H and inherent H within materials from the 1 Da and 2 Da peaks in the mass spectrum, making H analysis using APT very complicated and prone to major quantification uncertainties. This situation can be mitigated by introducing deuterium (D) in the form of D2O (heavy water), where D atoms appear at the 2 Da peak as D+ and 3 Da peak as DH+.
In this study, low-tin ZIRLO® [7] samples subjected to autoclave tests with H2O water for the first 10 days and 50% D2O water for the following 20 days were characterised by APT, nanoscale secondary ion mass spectrometry (NanoSIMS), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD) at the oxide/metal interface. The presence of D and supporting data from other techniques assist to better interpret the APT hydrogen data, and the novel insights of hydrogen ingress process can be utilised to understand the whole story of the oxidation process.
Reference:
1. Krishnan, R. and M.K. Asundi, Zirconium alloys in nuclear technology. Proceedings of the Indian Academy of Sciences Section C: Engineering Sciences, 1981. 4(1): p. 41-56.
2. Lemaignan, C. and A.T. Motta, Zirconium Alloys in Nuclear Applications, in Materials Science and Technology. 2006.
3. Lemaignan, C., Corrosion of Zirconium Alloy Components in Light Water Reactors. Vol. 13C. 2006, ASM International. 415-420.
4. Couet, A., A.T. Motta, and A. Ambard, The coupled current charge compensation model for zirconium alloy fuel cladding oxidation: I. Parabolic oxidation of zirconium alloys. Corrosion Science, 2015. 100: p. 73-84.
5. Porte, H.A., et al., Oxidation of Zirconium and Zirconium Alloys. Journal of The Electrochemical Society, 1960. 107(6): p. 506.
6. Meier, M.S., et al., Exploiting Adsorption Dynamics in Atom Probe Tomography for accurate Measurements of Hydrogen Concentrations. Microscopy and Microanalysis, 2022. 28(S1): p. 1650-1652.
7. Sabol, G.P., ZIRLO™ — An Alloy Development Success, in Zirconium in the Nuclear Industry: Fourteenth International Symposium, B. Kammenzind, Editor. 2005, ASTM International: West Conshohocken, PA. p. 3-24.
