Termal-hydraulic Behaviour

The natural circulation of the coolant produces the primary flow rates according to the power generated (and removed). Under different power transients a self-correcting response in the flow rate is obtained.

Due to the self-pressurising of the Reactor Pressure Vessel (steam dome) the system keeps the pressure very close to the saturation pressure. This has proved to be sufficient at all the operating conditions to guarantee a remarkable stability of the RPV pressure response.

The control system is capable of keeping the reactor pressure practically at the operating set point through different transients, even in case of power ramps. This is mainly due to the fact that neutronic phenomena are many times faster than thermal-hydraulic response.

The negative reactivity feedback coefficients and the large water inventory of the primary circuit combined with the self-pressurisation features make this behaviour possible with minimum control rod motion.

It may be concluded that the reactor has an excellent behaviour under operational transients.