Bottom Reflooding of Pressurized Water Reactors—Part I: Forced Reflooding and Core Thermal Hydraulics

An engineering model was developed to simulate the thermal-hydraulic phenomena in pressurized water reactor cores during bottom reflooding. The model couples the fluid thermal hydraulics and radial heat transfer in the fuel rods. The system dynamics were formulated in terms of a set of ordinary differential equations, which were integrated using the Gear integration package. A dynamic nodal scheme, which moves with the quench-front location, was utilized to predict the fuel rod temperatures. Model predictions and comparisons with full-scale experiments are provided, and show good agreement with the FLECHT-SEASET and Slab Core Test Facility data. The proposed methodology was found to be computationally fast when compared with previous approaches, and can be readily integrated with other modules to simulate the complete reactor coolant system.