Three-Dimensional Lagrangian-Eulerian Modeling and Analysis of Fuel-Coolant Interaction

Abstract

Fuel-Coolant Interaction (FCI) is a phenomenon in which hot molten fuel interacts with surrounding coolant during a nuclear reactor severe accident and the potential explosive outcome of such an event could threaten the reactor containment integrity. In this study, a multi-field, three-dimensional computational model has been developed to assess the plant safety by an energetic FCI. The molten fuel is modeled in Lagrangian frame and the liquid and vapor of coolant fluid are modeled in Eulerian space. The Lagrangian and Eulerian fields are coupled semi-implicitly. The breakup of molten fuel jet is modeled based on the physical mechanisms of Rayleigh-Taylor instability at jet front and Kelvin-Helmholtz instability at jet lateral surface. The interfacial heat and momentum transfer between phases are modeled based on flow regimes. The Lagrangian particles of fuel is treated as a parcel and its size is allowed to expand as the fuel breaks up. Verification of the model has been carried out for experimental data of prototypical molten fuel: KROTOS and TROI. The validation calculations showed that the present model is able to adequately simulate an energetic fuel-coolant interaction. Three-dimensional calculations of ex-vessel steam explosions in a PWR reactor cavity showed that the wall impulse in case of off-center entry of melt jet by 1 m is 50% higher than that of melt entry at the center of cavity.