The S8G reactor is the eighth nuclear fission reactor design finalized for use in powering U. S. Navy submarines by a division of the General Electric Corporation.
It is a natural circulation reactor, capable of operating at a significant fraction of full power without reactor coolant pumps.
The S stands for submarine, 8 for 8th reactor design, and G for General Electric. The S8G reactor provides nuclear power for operating the Ohio-class (SSGN/SSBN-726 Class) submarines in the U. S. Navy.
A land-based prototype of the reactor plant, built near Ballston Spa, New York, was used for testing and crew training throughout the 1980s. In 1994, the core was replaced with an S6W reactor , designed for the then-new Seawolf class.