Westinghouse AP600 and AP1000 passive safety cooling arrangements.

AP 1000 or 600 Passive emergency cooling

Westinghouse say that "The features of the passive safety systems include passive safety injection, passive residual heat removal, passive containment cooling, and passive main control room habitability maintenance. All of these passive systems have been designed to meet the NRC single failure criteria, and probabilistic risk analyses have also been used to verify their reliability. These passive systems employ natural forces and stored energy to operate; gravity, natural circulation and compressed gasses. They are highly reliable because in the unlikely event of an accident, with an assumed unavailability of non-safety systems, they do not require the starting of auxiliary motors, pumps, or diesel generators."