Zirconium cladding oxidation and hydrogen pickup is a complex multiphysics process governed by defect and charge transport in the presence of temperature and stress gradients, electric field, and inhomogeneous alloying element distribution. In reactor, the presence of irradiation complicates matters further still. Experiments have shown that precipitates of the alloying elements have significant impact on the oxidation kinetics, even though the precipitates themselves are initially incorporated in metallic form into the advancing oxide layer, undergoing corrosion much later than the matrix.
It is also clear that precipitates and precipitate distribution has a significant impact on the oxide growth. Thus, it is natural to expect that the oxide layer conductivity will be significantly impacted by the precipitate distribution. This effect appears to be due to the impact of the metallic precipitates on the charge transport. The impact of these precipitates is the driving force for changes that have been made to alloying elements in new cladding alloys.
To investigate the effect of second phase precipitates on oxidation kinetics, in-situ Electrochemical Impedance Spectroscopy is performed on selected alloys with different alloying element contents, second phase precipitate sizes and volume fractions. The oxidation kinetics and oxide conductivity is measured as a function of exposure time in high temperature, high-pressure conditions.
- A. Couet, A. T. Motta, A. Ambard, and D. Livigni, “In-situ electrochemical impedance spectroscopy measurements of zirconium alloy oxide conductivity: Relationship to hydrogen pickup,” Corrosion Science, vol. 119, pp. 1-13, 2017.
- A. Couet, A. T. Motta, R. J. Comstock, and A. Ambard, “Oxide Electronic Conductivity and Hydrogen Pickup Fraction in Zr Alloys,” Annual Meeting on Transactions of the American Nuclear Society and Embedded Topical Meeting: Nuclear Fuels and Structural Materials for the Next Generation Nuclear Reactors, NSFM 2014, Reno, NV, 2014, pp. 845-848.