Parametric Sensitivity Study on the Reflooding Models of the MARS Code Based on 6 × 6 Rod Bundle Test Results

The 6 × 6 reflood test facility for Advanced Thermal Hydraulic Evaluation of Reflood phenomena (ATHER) has been operated by Korea Atomic Energy Research Institute to investigate the reflooding phenomena in a rod bundle. A series of bottom reflood tests was carried out by varying several parameters affecting the reflooding process such as the flooding velocity, inlet coolant subcooling, system pressure, initial maximum rod wall temperature, and rod power. Subsequently, counterpart reflood tests of rod bundle heat transfer data from The Pennsylvania State University were conducted for comparison, focusing especially on the effects of the heat flux on the peak cladding temperature (PCT) and the quenching behavior. The best-estimate thermal-hydraulic system analysis code MARS3.1 was assessed with the obtained data to investigate the parametric effects on its prediction accuracy. It was found that the prediction accuracy of the PCT is reasonable on the whole but that the MARS code predicts delayed quenching behavior compared with the data, especially for high heat flux conditions. In particular, the prediction becomes deteriorated downstream, far from the inlet of the test section.