Passive systems are being considered for numerous innovative reactor concepts owing to their enhanced safety reliability and their reduction of costs associated with the maintenance of active parts. These systems take advantage of natural forces such as convection and gravity. In particular, the Safety Condenser (SACO) allows the decay heat removal through a passive cooling of the secondary side. The passive cooling is carried out by condensing the steam from the steam generator inside a submerged vertical heat exchanger (in a water pool), the condensate coming back to the steam generator by natural circulation. An accurate prediction of the condensation is thus required for the safety assessment of innovative concepts involving a SACO.

CATHARE is the reference thermalhydraulic system code used in France for safety assessment of the current fleet of pressurised water reactors (PWRs) and upcoming innovative reactor designs. The code is based on a six-equation two-fluid model and includes an extensive set of closure relations, which are validated with separate and integral effect tests. Regarding condensation, CATHARE standard models have been validated against the COTURNE separate effect tests involving gravity-driven flows with a certain extent of shear stress (i.e. Reynolds liquid film from 300 to 5000). These conditions are representative of the reflux condensation mode in PWRs (see Figure 1), but they are significantly different to the ones encountered in a SACO (i.e. Reynolds liquid film of up to 150000).

Over the last years, a significant number of experimental data involving condensation in a SACO have been generated. This is the case of the integral PKL test facility at Framatome Gmbh (Germany) and the ELSMOR integral facility at SIET (Italy), which have assessed the steady performance of a SACO under a wide range of thermal-hydraulic conditions. Preliminary studies at CEA have shown that the standard CATHARE correlation leads to an excessive cooling of the liquid film, which may have significant consequences in the transient evolution.

The main goal of this internship is to conduct a systematic assessment of CATHARE standard condensation model capabilities to describe the heat transfer in the SACO-operating region based on the available experimental database and to identify the aspects that require further efforts aiming at a later implementation in CATHARE. The experimental database will consist of several series of PKL and ELSMOR steady-state experiments, as well as data from other experimental facilities at PSI (Switzerland) and KAIST (South Korea).