Development of MERCURY for simulation of multidimensional fuel behavior for LOCA condition

During a loss of coolant accident (LOCA), the ballooning and rupture of fuel cladding can block coolant flow and reduce the coolability of a reactor, which can lead to violation of a safety criteria. It is crucial that fuel models consider how multidimensional thermomechanical behavior and burnup properties affect safety analysis and evaluation. In this study, a multidimensional entire fuel rod analysis module (MERCURY) based on the finite element method (FEM) was developed to simulate multidimensional fuel behavior during a LOCA. The MERCURY incorporated a transient thermal analysis model, a multidimensional gap conductance model, a nonlinear mechanical model, and a transient creep model as thermomechanical models. As fuel models, burnup-dependent material properties, an oxidation model at high temperature, a rod internal pressure model, and cladding burst criteria were developed. Each FEM-based model was verified against results using a commercial FEM package. Verifications demonstrated that the models were formulated and integrated correctly. As validation, the MERCURY simulated experiments (PUZRY) regarding cladding behavior out-of-pile at high temperature and high inner pressure, which is similar to the fuel condition during a LOCA. The simulation results show good agreement with measured hoop strain in experiment.