Within the Reactor Pressure Vessel (RPV) plant life time project, Electricite´ de France (EDF) must carry out studies showing the RPV integrity during severe loading conditions as the Small Break Loss Of Coolant Accidents (SBLOCA) scenarios. A recent thermal-hydraulic SBCLOCA scenario study, concerning a certain RPV geometry, showed two-phase-flow conditions appears in the cold leg. The single phase flow CFD tools, usually used in these cases, are unsuitable to carry out such studies. That is the reason why EDF is developing a new CFD code (called Neptune_Code) implementing two-phase flow models. In order to improve the physical phenomena knowledge and the existent experimental data for Neptune_Code development, EDF carried out an experimental study concerning the stratified flow (salt water) and free surface (water air) behavior during a representative ECC scenario with partial uncovered cold leg. This paper focuses mainly on the experimental method and the measurements obtained in three tests showing the effects of the uncovered cold leg level on the stratified flow and the free surface behavior.

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