Experimental study and modelling of the phase transformation of Zircaloy-4 alloy under high thermal transients

Dilatometry tests were performed to study the phase transformation kinetic of nuclear fuel claddings made of Zircaloy-4 upon fast heating rates (up to 2000 °C/s). These tests highlighted that from equilibrium to 500 °C/s the temperature at which the transformation starts shifts towards higher temperatures with increasing heating rates. Above 500 °C/s, no impact of the heating rate was observed. The temperature at which the transformation ends remains close to 960 °C with no clear dependence on heating rate. Metallurgical analyses were carried out and were in agreement with the results obtained by dilatometry. A phase transition model was identified from equilibrium to 2000 °C/s.