Deviations From Parabolic Kinetics During Oxidation of Zirconium Alloys
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Published:2015
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The oxidation of zirconium cladding alloys used in nuclear reactors was investigated under the conditions of loss-of-coolant and severe accidents, i.e., at temperatures between 600 and 1600°C and in various atmospheres. The kinetics were parabolic or sub-parabolic as long as the superficially formed oxide scale remained intact and protective. More or less linear kinetics were found after degradation of the oxide layer due to phase transitions connected with volume changes and formation of cracks and pores. The presence of nitrogen further accelerated oxidation rates by formation of zirconium nitride at the metal-oxide boundary and its re-oxidation with the progressing reaction. This paper summarizes extensive experimental work on high-temperature oxidation of zirconium alloys performed at KIT focusing on effects causing non-parabolic oxidation kinetics.