Why Not Nuclear-Powered Aircraft?

Why Not Nuclear-Powered Aircraft?
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We have nuclear submarines and nuclear ships, so why not nuclear planes?

Well, that's a very good question, one the United States spent $1.04 billion back in the 1950s trying to answer.

The idea for a nuclear-powered plane was originally hatched in 1944, during a time when the Manhattan Project was astonishing everyone with the potential of nuclear energy. Three years later, engineers at the newly established U.S. Air Force were awarded with initial funding of $10 million to research methods of wielding atomic power for aircraft. The request was buoyed by an obvious advantage: Theoretically, such a plane could remain aloft for weeks at time.

Under the new Aircraft Nuclear Propulsion program, Air Force engineers immediately went to work, developing three experimental engines (two of which are pictured below). By 1951, they settled on a method for directly transferring heat from a reactor and using it to propel an aircraft, described thusly in a 1963 government report:

"Air enters through the compressor, is forced into the reactor, and is heated by the fuel elements. After passing through the turbine, where energy is extracted to drive the compressor, the heated air is expelled at high velocity through the exhaust nozzle."

Concurrently, engineers at General Electric built a 2.5 Megawatt nuclear reactor designed specifically for a plane. It was a molten salt reactor, the first of its kind. Unlike the typical light water reactors used today -- where the uranium fuel is submersed in water -- a molten salt reactor utilizes a uranium-containing salt mixture as both a coolant and/or a fuel, allowing for a much smaller design. 

With everything coming together on the technical end and funding continuing to pour in, it was time to face a key practical roadblock: how to protect the crew from the radiation emanating from their own plane. Thus, the early 1950s saw engineers affixing a gargantuan 11-ton cockpit lined with lead and rubber to the head of a Convair B-36 "Peacemaker" bomber. By the middle of the decade, Air Force personnel loaded General Electric's reactor onboard via the bomb bay and switched it on during the majority of 47 test flights. The reactor didn't propel the aircraft or power any of its systems, however. The flights were purely intended to test the radiation shielding, and their results were promising.

"All the data collected by these tests showed the program managers that the possibility of using a nuclear power plant to provide an aircraft with unlimited operational range was indeed at their disposal at this time," Raul Colon wrote for Aviation History. Reports from the time back Colon's assessment.

Meanwhile, January 1956 brought successful ground tests of the X-39 engine, powered completely by a nuclear reactor. Forecasts of atomic jets by 1980, published in Popular Science, were apparently on schedule!

But then the bipolar nature of politics abruptly intervened. Hesitance towards nuclear power supplanted excitement in the late 1950s and early 1960s, and politicians and a public nervous about the escalating Cold War started viewing nuclear planes less as a futuristic life changer and more as a recipe for mobile meltdown. President Kennedy canceled the Aircraft Nuclear Propulsion program in 1961.

Every so often, a call for nuclear-powered planes resurfaces, but it's either ignored or swiftly shot down. Given the current regulatory attitude toward grounded nuclear energy, the ubiquity and safety of fossil fuel-powered flight, and advancements in electric aircraft, it's difficult to imagine that nuclear power will ever take wing.

(Images: USAF, Wtshymanski)

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