Development of Multiphysics Framework to Analyze Dynamic Gap Heat Transfer and Cross-Flow Effect on Partial Rod Ejection Accident

A coupling framework named Multi-Physics CORE (MPCORE) is developed to analyze the multiphysics phenomenon in a nuclear reactor. MPCORE performs two-way coupling between two physics modules. A rod ejection accident (REA) is an important design-basis accident that results in an instantaneous power surge in the case of prompt criticality. Hence, this technical note studies the passive response of a nuclear reactor core in the case of a similar rapid reactivity insertion. Stand-alone calculations by neutronics, thermal-hydraulic (TH), or fuel performance (FP) modules use conservative options for other physics modules. Thus, multiphysics analysis provides a more realistic assessment of actual prospective damage. MPCORE employs an adaptive time-step feature to reduce execution time. Moreover, it performs in-memory transfer of data between different modules. This technical note evaluates the performance of the TH module with cross flow (subchannel) and without cross flow (one-dimensional). For the FP module, the effect of dynamic and static gap heat transfer coefficient models is also quantified. Hence, four combinations with these two TH and FP options are simulated. The following are the safety parameters compared for different models: departure from nucleate boiling ratio, linear power, fuel enthalpy, fuel centerline temperature, cladding outer surface temperature, and coolant temperature.