Bottom Reflooding of Pressurized Water Reactors—Part II: Oscillatory Flow During Gravity-Feed Reflooding

A model was developed to simulate thermal-hy-draulic phenomena in the downcomer and lower plenum of a pressurized water reactor during reflooding. The system dynamics were formulated in terms of a set of time-dependent ordinary differential equations that were integrated numerically. A model was developed to simulate the oscillatory flow in the downcomer-lower plenum-core system. A numerical procedure was devised for solving the governing global momentum equation. This procedure is shown to be numerically stable and computationally efficient. The developed model for downcomer and lower plenum was coupled to the core thermal-hydraulic model, and predictions were made for FLECHT-SET experimental data. The results compared well with the experiment.