so it does not boil. This circuit operates at a temperature of around 250 to 300 C. Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.

The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers