A high-pressure natural convection loop (CAPCN) was constructed and operated to produce data in order to verify the thermal hydraulic tools used to design the CAREM integral LWR design, mainly the dynamical response. This is accomplished by the validation of the calculation procedures and codes for the rig working in states that are very close to the operating states of CAREM reactor. CAPCN resembles CAREM in the primary loop and steam generators, while the secondary loop is designed just to produce adequate boundary conditions for the heat exchanger. Water enters the heated section from the lower plenum. The nuclear core is simulated by electric heaters. The heated water flows up through the riser to the upper plenum where a liquid-vapor interphase exists. The water exits this plenum through an outer volume in contact with the steam generator. The steam generator has two coils, once through, secondary inside. The sub-cooled water flows down through a downcomer or cold leg to the lower plenum. Natural circulation flow may be regulated by a valve in the cold leg and a bypass to the bottom of the riser. This rig was constructed according to ASME for the following primary parameters: 150 bar and 340°C. The primary loop may operate in saturated or sub-cooled regimes, with a heating power up to 300kW and different hydraulic resistance. The circuit configuration allows the study of stationary states similar to CAREM conditions of pressure, specific flow and enthalpy. Height was kept in a 1:1 scale.

Many experiments were performed in order to investigate the thermal-hydraulic response of the system in conditions similar to CAREM operational states. The influence of different parameters like vapor dome volume, hydraulic resistance and dome nitrogen pressure was studied. Perturbations in the thermal power, heat removal and pressure relief were applied. The dynamic responses at low pressure and temperatures, and with control feedback loops were also studied. It was observed that around the operating point self-pressurized natural circulation was very stable, even with important deviation on the relevant parameters.

The data obtained is being used to test numerical procedures and codes. A sensitive analysis was performed and most sensitive parameters were identified. A representative group of transients were selected, in order to check computer models. Simulation models are in current development against a reference transient, without adjustment. When this contrast is clear, models will be compared against the representative group of transients. The information on specific models should be incorporated into CAREM modelling.