Effect of pH on Hydrogen Pick-Up and Corrosion in Zircaloy-4

The Minerals, Metals &amp Materials SeriesProceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors(2017)

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Abstract
Thermal desorption spectroscopy, secondary ion mass spectroscopy and scanning transmission electron microscopy have been used to investigate the effect of pH on corrosion and hydrogen pick-up behaviour in different samples of Zircaloy-4. Samples were autoclave-oxidised in pure water and at an elevated pH (with 50% deuterated water) when compared to commercial reactors. A characteristic desorption peak for hydrogen has been found at ~650 °C, which occurs when the difference in free energy between hydrogen in the metal and in the gas phase becomes positive. Electron energy loss spectroscopy provided us with a method to detect and measure the thickness of the following layers (from oxide to metal): ZrO2, a previously reported ZrO suboxide, an oxygen saturated zirconium region and the Zr metal. Overall, samples exposed to a high pH show a longer time to transition and contain far less hydrogen than those oxidised in pure water. A mechanistic explanation will be provided.
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Key words
Zircaloy-4, Hydrogen, Deuterium, Desorption
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