Passive systems are being considered for innovative reactors owing to their enhanced safety reliability. Particularly, the Safety Condenser (SACO) ensures the decay heat removal through a passive cooling of the secondary side: steam generated is condensed in a submerged vertical heat exchanger and the condensate returns back to the steam generator by natural circulation. It is therefore essential to accurately predict condensation in numerical codes.

CATHARE-3 is the reference thermalhydraulic code at system scale used in France for safety assessment of pressurised water reactors (PWRs). In particular, CATHARE standard film condensation models are validated against the COTURNE separate effect tests. Designed to validate reflux condensation mode in PWRs, the database involves gravity-driven flows with a certain extent of shear stress. However, the standard model is no longer valid for the SACO operating region, which is dominated by the sheer stress.

Recent works on SACO have shown a systematic overestimation of condensation by CATHARE. The main goal of this thesis is to improve CATHARE-3 condensation heat transfer models by means of experimental data (to be generated within the EASI-SMR European project) and by means of an upscaling methodology from CFD tools, namely Neptune_cfd.