Zirconium–niobium alloys are currently proposed for applications in water-cooled nuclear reactors. However, the mechanisms by which Nb impacts the corrosion resistance of these alloys are yet to be clarified. In this work, we utilize a thermodynamic framework informed by density functional theory calculations to predict the effect of Nb on the equilibria of charged defects in tetragonal ZrO2, and discuss how the changes in the defect concentrations affect the protectiveness of this oxide that grows natively on Zr alloys during oxidation. Our analysis shows that Nb dissolves predominantly in the oxidation state 5+ as a substitutional defect on the Zr sublattice, with charge compensation achieved by the negatively charged Zr vacancies. Moreover, Nb dissolution is limited to the oxygen-rich conditions, i.e., in the oxide surface facing oxidizing environment. We validate this finding by performing X-ray photoelectron spectroscopy on oxidized Zr–Nb alloys. The introduction of Nb in tetragonal ZrO2 is found to enhance the concentration of Zr vacancies and of free electrons and to decrease the concentration of oxygen vacancies. We conclude that the net effect of Nb on the corrosion kinetics of Zr alloys is favorable if the rate limiting process is oxygen transport, while Nb would be detrimental if electron transport limits the oxidation kinetics.

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Producing inexpensive hydrogen using electricity to split water or to extract hydrogen from hydrocarbon compounds is a two-sided coin: one side is obtaining and exploiting low-cost, emissions-free energy sources while the opposite side is establishing low-cost robust, durable, and efficient materials for the conversion processes. This article explores the materials needed for water splitting electrolysis, electrochemical abstraction of hydrogen from light alkanes, and looping thermal-chemical reaction processes that typically form and then dissociate an acid compound in a two- or three-step process. The focus is on the R&D needs of materials that are used for high-temperature electrochemistry, focusing on solid-oxide, ion-conducting cell materials sets (SOECs). To exploit the availability of low-cost electricity, these materials must stand up to cyclic operations. They also must be durable for years of service to reduce operating and maintenance costs, and they must achieve high conversion efficiencies to avoid large, energy-intensive recycle loops. Graphical abstract

In this work, a general methodology and innovative framework to characterize and quantify representativeness uncertainty of performance indicator measurements of power generation systems is proposed. The representativeness uncertainty refers to the difference between a measurement value of a performance indicator quantity and its reference true value. It arises from the inherent variability of the quantity being measured. The main objectives of the methodology are to characterize and reduce the representativeness uncertainty by adopting numerical simulation in combination with experimental data and to improve the physical description of the measurement. The methodology is applied to an industrial case study for demonstration. The case study involves a computational fluid dynamics (CFD) simulation of an orifice plate-based mass flow rate measurement, using a commercially available package. Using the insight obtained from the CFD simulation, the representativeness uncertainty in mass flow rate measurement is quantified and the associated random uncertainties are comprehensively accounted for. Both parametric and nonparametric implementations of the methodology are illustrated. The case study also illustrates how the methodology is used to quantitatively test the level of statistical significance of the CFD simulation result after accounting for the relevant uncertainties.