CATHARE is a system code developed by CEA, IPSN, EDF and FRAMATOME for PWR safety analysis. It can model light water reactors or test facilities using several available modules. Two-phase flows are described using a two-fluid six-equation model and the presence of non-condensable gases can be taken into account by one to four additive transport equations. The code allows a three-dimensional modelling of the pressure vessel. Successive sets of closure laws or "revisions " are developed in an iterative methodology of improvement. The Revision 6 of the closure laws is implemented in the Version V1.5. It includes models,
for the reflooding, the film condensation in presence of non-condensable gases, the interfacial friction in the core, the flashing.

CATHARE has a modular structure. Several modules can be assembled to represent the primary and secondary circuits of any PWR or of any analytical test or system test facility. They are 0-D, 1-D, 3-D modules available. All modules can be connected to walls, or heat exchangers with a 1-D conduction calculation. Many sub-modules are available to calculate the neutronics, the fuel thermomechanics, pump characteristics, accumulators, sources, sinks, etc.

All modules use the 2-fluid model to describe steam-water flows and four non-condensable gases may be transported. The thermal and mechanical non-equilibrium are described. All kinds of two-phase flow patterns are modelled: co-current and counter-current flows are modelled with prediction of the counter-current flow limitation. Heat transfer with wall structures and with fuel rods are calculated taking into account all heat transfer processes ( natural and forced convection with liquid, with gas, sub-cooled and saturated nucleate boiling, critical heat flux, film boiling, film condensation). The interfacial heat and mass transfers describe not only the vaporization due to superheated steam and the direct condensation due to sub-cooled liquid, but also the steam condensation or liquid flashing due to meta-stable sub­cooled steam or superheated liquid.

The range of parameters is rather large: pressure from 0.1 to 16 MPa, liquid temperature from 20°C to 1800°C, fluid velocities up to supersonic conditions, duct hydraulic diameters from 0.01 to 0.75 m.

An important experimental program was carried out as a support for the development and validation of the code.