S6W Advanced Fleet Reactor

The S6W Advanced Fleet Reactor that powers the SEAWOLF Class is revolutionary in the military sense -- quietness and more efficient performance. It is not a radical design from a safety standpoint. The reactor is a typical Naval pressurized water reactor. S6W is large reactor plant designed to fit in the 40 ft (12.2 m) diameter hull of a Seawolf (SSN-21)-class sub.

Like the S8G reactor plant in Ohio-class SSBNs, S6W is believed to be designed for natural circulation core cooling and is capable of operating at a significant fraction of full power without reactor coolant pumps.

There was no separate S6G prototype. The original S8G core in the S8G prototype was replaced with an S6W core. The advanced fleet reactor was installed in the S8G prototype plant for testing, and the S8G prototype plant with the Advanced Fleet Reactor operated exactly as it has for the past 12 years. That reactor went critical in March 1994 and operated well. Putting the new reactor in a prototype affords the opportunity to operate it before introduction into the fleet, run it harder than in the fleet to determine its peak performance, and test its long-term properties. For the shipboard plant, the reactor core was loaded March 1995 and the ship's pre-commissioning crew began operating reactor plant systems. S8G operation with the S6G core continued until 2014.

The three Seawolf-class SSNs are the only subs using S6W. The 1st core was loaded on USS Seawolf (SSN-21) in March 1995. The propulsion plant consists of 1 x S6W reactor rated @ 270 MWt (est); 2 x steam turbines delivering a combined 52,000 shaft horsepower (38.8 MW) to a single pump-jet propulsor.