Zircaloy-4 fuel pin failure under simulated loss-of-coolant-accident conditions: Creep and rupture

This paper presents a detailed investigation of the creep and rupture behavior of Zircaloy-4 (Zry-4) fuel claddings used in Indian Pressurized Heavy Water Reactors (IPHWR) under simulated Loss-Of-Coolant Accident (LOCA) conditions. Fuel claddings are pre-oxidized in the steam environment at 500 °C to mimic the oxygen pickup during normal reactor operation. The burst tests are then performed on these preoxidized tubes at different heating rates (55–115 K/s) and internal overpressures (15–45 bar) in the steam environment, creating LOCA-like scenario in a high burnup condition, wherein the claddings further oxidize while undergoing deformation and rupture. The burst stress correlation is developed for IPHWR claddings from the obtained burst temperature and oxygen concentration data. A burst criterion model is developed by solving available creep rate, oxidation rate, and phase transformation equations simultaneously to study the effect of various parameters on burst characteristics of the fuel cladding. The proposed burst criterion model agrees well with the present and previous experimental burst data. Also, the ballooning progression predicted from the model is validated with the present and previous experimental data. In addition, the effect of available correlations for the creep rate, phase boundary temperature, and oxidation factor on the burst characteristics has been presented.