Sodium at sea

One of nuclear power’s forgotten historical byways is General Electric’s pursuit, for over a decade after WWII, of what they called an “intermediate” reactor cooled by liquid sodium. Most nuclear machines slow down the “fast” neutrons expelled by nuclear fission, resulting in “thermal” or slow neutron reactors. More futuristic breeder reactors deliberately do not slow neutrons down at all. GE had the bright idea of using neutrons of “intermediate” speed, between the two extremes. It’s fair to say nobody outside GE held much hope for this concept, and GE tried various incarnations of its idea, desperately seeking ways to obtain U.S. government funding. They successfully sold the notion to Admiral Rickover, then designing and building the first nuclear submarines. Rickover ran a beauty contest between GE’s design and his own preferred design utilizing plain old water.

GE ran into two problems when designing firstly a land prototype reactor, and secondly a larger submarine reactor, based on intermediate neutrons. Firstly, they got the theory wrong and discovered such halfway-speed neutrons don’t work well at all. Secondly, they used liquid sodium as coolant. Liquid sodium has since been used time and time again as coolant for fast neutron breeders, but what distinguished GE’s efforts, of course, is that they wanted to stick liquid sodium in a submarine that would spend its life underwater. Sodium and water do not coexist. They flash explosively. GE’s reactor ended aboard the USS Seawolf, a nuclear submarine that roamed seas for two years from 1957. Sodium kept leaking and by 1960, the GE concept was dead.

The reason GE’s Sodium Intermediate Reactor is now forgotten is that it never featured as a possible design for power reactors. It was military, and as a failed military experiment, soon vanished from public view. My book won’t cover it either, for that reason, but I do find the entire saga interesting as an example of a technological misstep. Rickover’s staff coined a few post-experiment jokes at GE’s expense, after the event of course. An exuberant GE engineer, Salomon Levy, even quipped in his memoirs, issued half a century later:

When questions arose about the use of a liquid metal for coolant aboard the submarine Seawolf, the joking response attributed to the Admiral was the General Electric (GE) would have invented a water-cooled reactor if the oceans were made up of liquid sodium.

Levy, Salomon. 2007. 50 Years in Nuclear Power: A Retrospective. American Nuclear Society, Chicago, Illinois, p. 14.