The two Pipe Ducts between Pressurizer and Reactor Vessel connect hydraulically the top and the bottom of the respective cold water plena in order to create a common cold water plenum.

The choice of two connection levels makes natural circulation possible in case of temperature difference between cold plena. If the normal decay heat removal route (i. e. the active steam/water system) is lost, the

uninsulated wall portion of the Pressurizer would thus help removing by conduction the decay heat towards the Plant Pool.

Conveyed water to and from each vessel, belonging to a common cold water plenum, does not significantly contribute to the thermal loadings on the pressure boundary during transients.

Air Coolers

Two finned-tube Air Coolers are arranged in loops in natural circulation.

Each Air Cooler is rated 1 MWth at 30 °С ambient air and 95 °С pool water inlet temperature.

The onset of natural circulation occurs every time the pool water temperature becomes higher than the ambient air temperature.

Operation of the air coolers would prevent, for unlimited time, the pool water from boiling, in case of long-term loss of the operational decay heat removal system.

The technology of the air coolers in natural circulation is derived from the design and operating experience of ANSALDO in the field of the LMFBRs.