Numerical study on PWR fuel rod cladding ballooning and burst behavior with the thermo-mechanical coupling finite element method

The ballooning behavior of fuel rod cladding is an important issue of nuclear reactor, which may initiate a severe nuclear reactor accident. Based on COMSOL multi-physical module, this research established a thermo-mechanical coupling finite element model, which can accurately simulate the distribution and evolution of temperature, strain, and stress of the fuel cladding under high temperature and pressure. The validation results indicated that the maximum deviations of the predicted temperature and strain are 8 % and 11 %, respectively, in comparison to the experimental data. Moreover, the burst data predicted by the model were consistent with the results of Yadav experiment. These tests encompassed a heating rate of 2 K/s to 8 K/s and an internal overpressure range of 1 MPa–9 MPa. The burst temperature predicted by the model decreased with the increase of internal overpressure, from 1315 K to approximately 1014 K. This trend was consistent with that observed in the experimental data, thereby verifying the model's accuracy and reliability. The effects of key parameters such as cladding heating rate and cladding internal pressure on cladding ballooning and burst behavior were further analyzed. The results indicated that as the heating power increased, the cladding burst temperature rose from 1055 K to 1290 K, while the burst strain decreased from 68 % to 27 %. When the internal overpressure rose from 3 MPa to 7 MPa, the burst strain and stress increased by 93 % and 174 %, respectively. This study elucidated thermo-mechanical cladding response, facilitating predictive safety analysis and optimal fuel rod design to mitigate loss-of-coolant accident risks in nuclear reactors.