The corrosion of zirconium alloy fuel cladding is a critical issue in current Light Water Reactors (LWRs). The main goal of this cladding is to ensure the fuel rod structural integrity to keep a coolable geometry in both operating condition and accident scenario.
Because hydrogen ingress into zirconium cladding can cause embrittlement and limit cladding lifetime, hydrogen pick-up during corrosion is a critical life-limiting degradation mechanism for nuclear fuel. This is especially true for the higher fuel duties currently used in the industry. However, mechanistic knowledge of the oxidation and hydrogen pick-up mechanisms is still lacking. In an effort to develop such knowledge, a comprehensive study is being conducted including detailed experiments combined with oxidation modeling. This study contains a set of experimental and modeling results conducted on zirconium alloys and articulates them into a general and unified corrosion theoretical framework.
A general hypothesis, which states that hydrogen pickup during corrosion results from the need to balance charge during the corrosion reaction, such that hydrogen pickup fraction decreases when the rate of electron transport through the protective oxide increases is currently tested using the Coupled Current Charge Compensation (C4) model under development. The C4 model is an analytical zirconium alloy corrosion model based on the coupling of oxygen vacancies and electron currents is developed. This model yields the oxidation kinetics, oxidation potential and space charge across the oxide.
A. Couet, A. T. Motta, A. Ambard, and R. J. Comstock, “Hydrogen Pickup Mechanism in Zirconium Alloys,” in 18th International Symposium on Zirconium in the Nuclear Industry, Hilton Head Island, SC, 2016, pp. 312-349.
A. T. Motta, A. Couet, “Zirconium Alloy Corrosion and Hydrogen Pickup,” in 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 2016, New Orleans, LO, 2016.