Uniform corrosion of zirconium alloy fuel cladding and the associated hydrogen pickup is a potential life-limiting degradation mechanism for nuclear fuel cladding in existing and advanced light water reactors, since hydrogen ingress can cause cladding embrittlement. Thus, it is of great interest to fuel vendors and utilities to limit cladding embrittlement both by decreasing the overall corrosion and by decreasing the amount of hydrogen ingress for a given corrosion rate. It has been pointed out that several factors can affect the uniform corrosion of zirconium alloys. Optimization of alloying elements is one of the key factors to obtain a zirconium-based alloy that is resistant to corrosion and that has low hydrogen pickup. Although extensive empirical knowledge is available, a mechanistic understanding of the role alloying elements in the corrosion and hydrogen pickup mechanisms is still lacking.
To measure hydrogen concentrations in zirconium alloys two techniques have been used: a destructive technique, Vacuum Hot Extraction, and a non-destructive one, Cold Neutron Prompt Gamma Activation Analysis. The results of both techniques show that hydrogen pickup fraction varies significantly with exposure time and between alloys. A possible interpretation of the results is that hydrogen pickup results from the need to balance charge. That is, the pickup of hydrogen shows an inverse relationship to oxidation kinetics, indicating that, if transport of charged species is rate limiting, oxide transport properties such as oxide electronic conductivity play a key role in the hydrogen pickup mechanism. Alloying elements (either in solid solution or in precipitates) would therefore impact the hydrogen pickup fraction by affecting charge transport.
- J. Romero, J. Partezana, R. J. Comstock, L. Hallstadius, A. T. Motta, and A. Couet, “Evolution of Hydrogen Pickup Fraction with Oxidation Rate on Zirconium Alloys,” in Top Fuel Reactor Fuel Performance, Zurich, Switzerland, 2015, pp. 476-482.
- A. Couet, A. T. Motta, and R. J. Comstock, “Hydrogen Pickup Measurements in Zirconium Alloys: Relation to Oxidation Kinetics,” Journal of Nuclear Materials, vol. 451, no. 1-3, pp. 1-13, 2014.