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

Laurent Laborde (1) , Ignacio Gomez Garcia Torano (2)

1 IRSN/PSN-RES/SAM/LEPC - Laboratoire d'Etude de la Physique du Corium
2 SIS2M UMR 3299 - Service Interdisciplinaire sur les Systèmes Moléculaires et les Matériaux (ex SCM)

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

Domaines: Physique [physics]

Laurent Laborde, Ignacio Gomez Garcia Torano. Modelling reflooding of intact core geometries in ASTEC V2.1: Improvements and validation on PERICLES experiments. Nuclear Engineering and Design, 2021, 378, pp.111157. ⟨10.1016/j.nucengdes.2021.111157⟩. ⟨hal-03375548⟩