The Nuclear Submarine In The Middle Of The Desert: The Story Of The S5G Natural Circulation Reactor

The Nuclear Submarine In The Middle Of The Desert: The Story Of The S5G Natural Circulation Reactor

 

From inl.gov (PDF file):

Then in 1961 came the S5G prototype (the 5th submarine design, made by General Electric). As the Cold War intensified, the United States and the USSR poured their latest technology into the theory and practice of undersea warfare. They wired the ocean floors with sound detectors. These called forth technology to quiet the submarines. One source of noise came from the pumps that circulated the coolant through the reactor and kept it under pressure. The art of sound detection became so refined that skilled listeners could identify the unique sound patterns of individual boats. So the mission of S5G was to eliminate noise.

S5G, like S1W, was built in a huge box of a building, its roof presenting an inscrutable flat surface to satellite cameras passing overhead. The reactor went critical for the first time in September 1965. The hull section floated in a “basin” of water. Operators inside the hull used equipment to make the hull rock back and forth, adding more realism to the simulation. In this setting, the Navy developed a method of circulating the reactor’s cooling water without using a pump and exploiting the principle that warm water rises. USS Narwhal was the first boat equipped with the system. At high speeds, pumps were still needed, so the controller could move the coolant either by socalled “forced” or “natural” methods.

And more formerly Top Secret info from Wikipedia:

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 same propulsion setup was used on both the USS Narwhal and the land-based prototype.

The concept of a natural circulation plant was relatively new when the Navy requested this design. The prototype plant in Idaho was therefore given quite a rigorous performance shakedown to determine if such a design would work for the US Navy. It was largely a success, although the design never became the basis for any more fast-attack submarines besides the Narwhal. The prototype testing included the simulation of essentially the entire engine room of an attack submarine. Floating the plant in a large pool of water allowed the prototype to be rotated along its long axis to simulate a hard turn. This was necessary to determine whether natural circulation would continue even during hard maneuvers, since natural circulation is dependent on gravity.

Comments

[Nick]

As I recall, they built another "dry sub" at the same time they built the USS Nautilus. Because the development timeframe was so tight on the Nautilus, and they were still figuring out how to get all the nuclear equipment to work right, they built two. One to float, and a replica so that engineers could move around the propulsion system, as a better than scale model. When they needed to make changes to one, it was easy to make changes to the other because they had a replica working model.

[dad29]

That also 'splains the nuker-captain qualification-test question "What do you do if the sub turns upside-down?"--in a natural system, that might create real cooling problems.