Modelling reflooding of intact core geometries in ASTEC V2.1: Improvements and validation on PERICLES experiments

The injection of water into core (core reflooding) is a key Accident Management strategy to prevent or mitigate degradation in water-cooled nuclear reactors. Among the flow regimes implicated during reflooding, most significant one terms heat transfer removal transition boiling, which takes place over short distance near quench front. In ASTEC V2.1 integral severe accident code, user can select among two concurrent two-phase thermalhydraulics modelling (five- six-equation scheme) and for each one, alternative reflooding models describe boiling region (TBR). On hand, DROPLET model calculates large coefficient user-defined above other EXPCHF flux downstream by imposing Critical Heat Flux at front prescribing an exponentially decreasing along flow-dependent length. This article aims selecting appropriate evaluation associated with both five hydrodynamic model. For that purpose, experimental data from PERICLES facility dealing intact geometries have been used. After exhaustive analysis different models, this study has found should be selected when using five-equation scheme, since it provides enough rod precooling However, benefits larger amount liquid available last combination gives best results on simulated tests thus recommended reactor applications.