Nov 5

The Atomic Buoy Experiment

Thursday, November 5, 2015 12:01 AM


buoy batteries

Batteries being loaded into the Atomic Buoy. Curtis Bay, Maryland, December, 1962. USNI Archives.

It’s not every day that the deployment of a navigational aid is attended by great fanfare, but that is exactly what happened on December 15th, 1961 at the Coast Guard Yard in Curtis Bay, Maryland. That afternoon, the U. S. Coast Guard launched its grand experiment for the world of tomorrow: the new Atomic Buoy.

Wait–the new what?

Eight years earlier, on December 8th, 1953, President Dwight D. Eisenhower stepped to the podium in the U.N. General Assembly hall in New York City to deliver an address on a topic that had been weighing heavily on the minds of many for the past eight years: atomic warfare. In the few years since the first atomic bomb exploded in the desert near Alamogordo, New Mexico, on July 16th, 1945, the new weapons had proliferated throughout the world, and by 1953 stockpiles were increasing daily. To help assuage public fears, Eisenhower made a proposal for the peaceful use of atomic energy:

“It is not enough to take this weapon out of the hands of the soldiers. It must be put into the hands of those who will know how to strip its military casing and adapt it to the arts of peace.

The United States knows that if the fearful trend of atomic military buildup can be reversed, this greatest of destructive forces can be developed into a great boon, for the benefit of all mankind.”

Eisenhower’s announcement marked the beginning of a new program that came to be known as “Atoms for Peace” whose purpose was to study, develop, and supply harnessed nuclear energy for peaceful civilian purposes.

The Atomic Buoy being readied for deployment. Curtis Bay, Maryland, December, 1962. USCG Photo. USNI Archives.

The Atomic Buoy being readied for deployment. Curtis Bay, Maryland, December 15th, 1962. USNI Archives.

One of the focuses of these new research efforts, beyond civilian nuclear reactors, was the development of compact radioisotope-powered electrical generators. Called Systems for Nuclear Auxiliary Power (SNAP), the program sought to harness the thermal energy (heat) given off by the decay of radioactive elements.

The trick of the design came from using this heat given off by the radioactive decay to produce electricity via the thermoelectric effect. German scientist Thomas Johann Seebeck had discovered in 1821 that when two dissimilar metals are coupled together in a closed circuit, an electric voltage is produced when the two metals are kept at different temperatures. The same principle is also found to work with modern semiconductor materials. With one heat sink provided by the source, and one cold sink tied to the external environment, these thermocouples, as they are known, can generate a great deal of electricity in a fairly compact system.

What made atomic energy particularly attractive for this type of power generation was the potential long life of the power source. Radioactive elements can produce heat for many years as they decay; the time it takes for half of that element to break down is called the half life. For example, the radioactive isotope Strontium-90, used in the SNAP generators, which is available in large quantities from processed nuclear reactor wastes, has a half-life of 28.5 years, meaning that tens of years of useful service life could be obtained from the initial fueling. As the element decayed over time, though, the amount of power generated would naturally decrease.

But even in spite of the gradual loss of the energy source, the cost savings of such a system could be enormous. With no moving parts and just the radioisotope thermoelectric generator producing electricity, a system powered by the SNAP generator would require little human intervention or refueling to keep working for long periods after its initial setup. Even in accessible places, such is in Curtis Bay, the costs of transporting alternative energy sources to a system and providing routine service can be great. That is even more so in remote places, where navigational buoys were most necessary. In spite of the initial cost to build and install the atomic generator, the money saved over the years trough decreased servicing needs would more than make up for the initial investment–or so it was hoped.

An artists' conception of the Atomic Buoy. USCG Photo. USNI Archives.

An artists’ conception of the Atomic Buoy. USNI Archives.

It was for these reasons that the Coast Guard first became interested in an atomic-powered lighted buoy. With a stable, long-term power source and requiring limited servicing, the generators seemed like a perfect fit for lighted navigational buoys. And so the Atomic Energy Agency contracted with the Martin Marietta Corporation to design and build just such a buoy in 1961. The generator they designed, designated the SNAP-7A, was one of a lineage of those tested for other purposes, including for powering earth-orbiting satellites and a Weather Bureau arctic weather station. (A successor, the SNAP-7B, would power the Coast Guard’s Atomic Lighthouse in Baltimore). Outputting 10 Watts of power, the generator was wired to a 7500-candlepower beacon that could be seen for 15 miles or more and installed in a typical Coast Guard buoy as a very practical counterweight. Together with its other systems, it was hoped the beacon could operate maintenance-free for over two years.

buoy schematic

Schematic of the Atomic Buoy showing its major parts. USNI Archives.

That was the hope anyway. It was found soon after the buoy’s launch that the gradual power loss expected with the radioactive decay of the Sr-90 isotope power source was far greater than had been anticipated — so much so that the SNAP-7A generator would require renewal in an impractically short amount of time for the cost. The grand experiment was a dismal failure. The buoy was quietly removed from Curtis Bay in 1966, and the generator itself was disassembled in 1969.

Further experiments with other radioisotope thermoelectric generators, including in the Atomic Lighthouse, a Navy test with a NOMAD weather station buoy, and in an experimental, steam-powered underwater acoustic beacon, were also considered failures for a number of reasons — though the primary one being that seawater and electrical components do not mix well. Most terrestrial reactors were out of service by the 1970s, though some of the old SNAP reactors are still around in today.

That is not to say however that the idea of an atomic generator has been a total failure. Such reactors have proven quite valuable in space exploration, including on the New Horizons spacecraft that has been flying by Pluto since this past July. With increasing attention being paid to renewable and other non-fossil-fuel sources of energy, it is possible that we may yet see another Atomic Buoy in the future.