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The concentration of oxygen in the primary β-phase of Zr-1%Nb alloy was investigated using SIMS and thermal evolution analysis (TEA). The specimens were as-received or preoxidized in water vapor (425 • C/10,7 MPa) to simulate the reactor conditions. Then the specimens were exposed to hot water vapor (0,1 MPa) and high temperatures (950-1200• C) for variable time intervals, which simulated the Loss of Coolant Accident (LOCA). The specimens were quenched in water with ice. Both SIMS and TEA quantitative results were in good agreement and were correlated with the mechanical properties (microhardness, residual ductility), which depend on the oxygen concentration and are important for the safety analyses assessment. The ceiling concentration of oxygen in the β-phase was established based on the experimental results of SIMS and TEA.

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Zry-4 fuel cladding tubes were exposed in mixtures of oxygen and nitrogen at temperatures of 800–1380 °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 °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 β-phase shrinked when the oxide scale along with the α-Zr(O) layer progressed. Eventually, both the specimen plastic strain and maximum load decreased due to the shrinkage and increasing embrittlement of the prior β-phase.