Adrien Couet1 Arthur Motta2

1, University of Wisconsin - Madison, Madison, Wisconsin, United States
2, The Pennsylvania State University, State College, Pennsylvania, United States

The development of corrosion resistant alloys for nuclear applications has been highly empirical in nature. Although in-reactor materials’ performances have constantly been improved, fundamental understanding of corrosion processes are clearly lacking. For instance, the specific effects of very small alloying elements addition in zirconium fuel cladding, either in solid solution or in precipitates, on oxidation kinetics and hydrogen pickup are still not understood. In addition, physically based corrosion models are critically needed to (i) predict materials’ behavior during normal and accidental conditions (ii) understand the role of alloying elements and (iii) characterize the complex coupling effects between corrosion and irradiation.
A holistic approach including precise oxidation kinetics and non-destructive hydrogen pickup measurements, coupled with microbeam synchrotron X-Ray Absorption Near-Edge Spectroscopy (XANES) experiments and in-situ Electrochemical Impedance Spectroscopy (EIS) data, has shed light on the alloying elements effects on corrosion and hydrogen pickup in zirconium fuel cladding. In parallel, a novel physically based corrosion model called Coupled Current Charge Compensation (C4) has been developed, which models the coupled oxygen vacancies, electron and proton currents through the oxide. The C4 model can calculate the oxidation kinetics, hydrogen pickup and space charge across the oxide to predict oxidation and hydrogen pickup kinetics of fuel cladding in normal and accidental (Loss Of Coolant Accident) conditions. The recent C4 implementation and validation into the nuclear fuel performance code BISON will also be presented.
Recently, specific research programs at the University of Wisconsin-Madison have aimed at validating the C4 model further and characterizing the neutron and photon irradiations effects on corrosion. The neutron irradiation effect on corrosion kinetics has been investigated in the framework of the C4 model on ZrNb model alloys using proton irradiation. The proton irradiation induced Nb redistribution has been characterized and its consequence on fuel cladding corrosion mechanism will be discussed. Finally, in-situ photo-corrosion experiments are under development to characterize the effects of photons (UV to hard X-Rays) on corrosion kinetics and hydrogen pickup. The general findings will be summarized and the applicability of this holistic approach to other alloy systems in extreme environments relevant to nuclear energy (molten salts, sCO2 and liquid sodium) will be discussed.