Peridynamic investigation on thermal fracturing behavior of ceramic nuclear fuel pellets under power cycles

A coupled thermo-mechanical bond-based peridynamic model is developed to investigate thermal fracturing behaviors, including random initiation and subsequent propagation of interacting thermal cracks, in ceramic nuclear pellets under power cycles. To go beyond the differences of typical time scales between thermal and mechanical systems, a multi-rate time integration scheme is introduced to the numerical model. A penalty method for contact between the fuel pellets and cladding is also incorporated into the coupled model. Two benchmark examples are provided to prove the correctness and accuracy of the proposed numerical model. Thermo-mechanical fracturing behaviors of fuel pellets under power cycles are then investigated using the coupled bond-based peridynamics, that can accurately predict realistic thermal crack patterns, including both radial and circumferential cracks. From the numerical results, it is found that radial cracks occur during power rises, but circumferential cracks initiate when the power is ramped down. The numerical results are in good agreement with previous experimental observations. In addition, the influence of cyclic power amplitude, cyclic power rate, cyclic power types, and convective heat transfer between fuel pellets and cladding on thermal fracturing behaviors of fuel pellets are studied. The numerical results can provide references for the design of nuclear fuel pellets.