Still waiting to hear if your observations are based on actual experience and/or personal knowledge?
The navy uses PWR's, a closed loop system, as opposed to BWR's an open loop system, an open loop system is one which the steam is generated in the reactor and flows through the turbine and auxiliaries and back to the reactor, a closed loop system is one where the heat is generated in the reactor and the heat is exchanged in heat exchangers with a secondary loop in which the steam is generated.</P>
The advantage of the first is a secondary system that is not Hot outside of containment, the second cost.