S5G reactor

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The S5G reactor is a prototype naval reactor designed for the United States Navy to provide electricity generation and propulsion on warships. The S5G designation stands for:

S = Submarine platform
5 = Fifth generation core designed by the contractor
G = General Electric was the contracted designer

This nuclear reactor was installed both as a land-based prototype at the Nuclear Power Training Unit, Idaho National Engineering Laboratory near Idaho Falls, Idaho, and on board the USS Narwhal (SSN-671). It was intended to test the potential contribution of natural circulation technology to submarine quieting. ^[1]^[2]^[3] Reactor primary coolant pumps are one of the primary sources of noise from submarines, and the elimination of coolant pumps and associated equipment would also reduce mechanical complexity and the space required by propulsion equipment. Its design was the direct ancestor of the S8G reactor used on the Ohio class submarines.

To further reduce engine plant noise, the normal propulsion setup of two steam turbines driving the screw through a reduction gear unit was changed instead to one large propulsion turbine with no reduction gears. This eliminated the noise from the main reduction gears, but the cost was to have a huge main propulsion turbine. The turbine was cylindrical, about 12 feet in diameter, and about 30 feet long. This massive size was necessary to allow it to turn slowly enough to directly drive the screw and be fairly efficient in doing so. The propulsion setup was used on both the USS Narwhal and the land-based prototype.