High-Temperature Steam Oxidation Kinetics and Mechanisms of Cr-Coated Zr Alloy Claddings

The Cr-coated Zr alloy materials appear to be one promising short-term accident tolerant fuel cladding concept, due to their outstanding high-temperature oxidation resistance and improved resistance to fretting wear. In addition, there are few barriers or challenges to be applied to nuclear reactors for coated Zr alloy claddings. In this work, uniform and dense Cr coatings with thickness of 12-15 μm were deposited by magnetron-sputtering process on the outer surface of Zr-1Nb alloy tubes. Two-sided isothermal oxidation tests were performed in flowing steam by synchronous thermogravimetric analyzer, at temperatures ranging from 1000 °C to 1200 °C and for oxidation time ranging from 300 s to 5000 s, with the object of systematically studying the high-temperature steam oxidation behavior of Cr-coated Zr alloy cladding during reactor accidents. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction were utilized to characterize the microstructure, oxide layer thickness, element distributions and phase of oxide scale to study the oxidation kinetics and mechanisms of Cr coating. Based on these analyses, dense chromia scale is developed on the outer surface of cladding during steam oxidation, preventing the oxygen atoms from diffusing into the substrate, to improve the high-temperature resistance of the composited claddings. In addition, the oxidation kinetics of the Cr coating is nearly parabolic and the rate constants is at least two orders of magnitude lower than the Zr alloy, enhancing high-temperature steam oxidation resistance of Zr alloy claddings. © 2023 Rare Metals Materials and Engineering Press. All rights reserved.