HIGH TEMPERATURE OXIDATION OF ZRY-4 IN OXYGEN-NITROGEN ATMOSPHERES

Zry-4 fuel cladding tubes were exposed in mixtures of oxygen and nitrogen at temperatures of 800 - 1380 degrees C. The influence of various flow rates of oxygen and nitrogen as well as specimen height on the weight gain was examined. Metallographic observations were carried out and residual mechanical properties were assessed employing ring compression tests (RCT). The overall weight gain was substantially affected by both the applied flow rates and the height of specimens. The oxidation kinetics in air was assessed based on the results of weight gain measurements. A transition in the kinetics was observed at 800 and 1000 degrees C. The kinetics in the post-transient regimes was rather accelerated than linear. The equation proposed in this study for air condition was in good agreement with the Leistikow-Berg correlation for air condition and the Baker-Just correlation for steam condition. Prior beta-phase shrinked when the oxide scale along with the alpha-Zr(O) layer progressed. Eventually, both the specimen plastic strain and maximum load decreased due to the shrinkage and increasing embrittlement of the prior beta-phase.