CATHARE is a 2-fluid thermal-hydraulic code capable of simulating thermal and mechanical phenomena occurring in the primary and secondary circuits of PWRs for a wide variety of accidental situations. The description of the flow is essentially 1-dimensional. Closure laws concerning mass, momentum and energy exchanges between phases and between each phase and the walls are required. A set of specifically designed separate effect experiments were performed and analysed. Having regard for some development principles, correlations are established on the basis of experimental data. The mechanical transfer laws are derived first from experiments where thermal non equilibrium is negligible. Using them as a basis for further interpretation of experimental data, interfacial heat transfer laws are then developed. Wall heat transfer correlations then have to be fixed. All these steps are presented with emphasis being placed on the most recent developments. These last investigations concern the direct contact condensation, stratification model, wall friction, droplet break up and scale effect, geometrical effect and pressure effect on the interfacial friction.
