Behavior of zirconium fuel cladding under fast pressurization rates

Rapid pressurization test was carried out to evaluate the mechanical behavior of the zirconium cladding under a fast strain rate as well as a biaxial stress state for simulating an out-of-pile reactivity initiated accident (RIA) behavior. Influence of temperature, hydrogen content and alloying elements have been addressed in the conducted mechanical tests. The results showed that pressurization rates of 5.4 GPa/s at room temperature and 3.1 GPa/s at 350 °C were achieved. The corresponding time to failure was similar to expected power transient duration during a RIA. Maximum hoop stress of Zircaloy-4 at room temperature and 350 °C increased, respectively by 24.3 and 16.8% when compared to the conventional burst test results. Failure mode switched from a ductile ballooning to a brittle failure which leads to an axial split of the cladding when the hydrogen was added at a nominal value of 600 ppm. When the test temperature increased, its effect was diminished. Addition of an alloying element influenced the mechanical property differently. Niobium acted beneficially against hydrogen embrittlement in that it increased the ductility of the metal matrix.