We know that it is possible to build a jet airplane powered by nuclear reactors. Whether it is possible to build it without killing the crew remains unclear.

In the early Cold War, before ICBM technology matured, the US Air Force seriously considered what now seems quite strange: building a nuclear-powered aircraft that could remain airborne for extraordinary periods without dependence on conventional jet fuel.

The effort, initially known as the Nuclear Energy for the Propulsion of Aircraft (NEPA), later evolved into the Aircraft Nuclear Propulsion (ANP) program in 1951. The logic of the program was intuitive; if a bomber could remain airborne for days at a time, it could provide persistent nuclear deterrence against the Soviet Union, in much the same way that today’s nuclear submarines (SSBNs) do. A bomber perpetually in the air would be impossible to catch unawares in a preemptive strike; it would guarantee the United States a second-strike capability against the USSR, making a nuclear war unwinnable.

But things weren’t so simple from a technological side. For the project to succeed, engineers would have to put an operational nuclear reactor inside an aircraft and figure out how to use it to power the engines, while keeping the vehicle light enough to fly—and shielding the crew from radiation. After investing 15 years and about $1 billion in the project, the US canceled it in 1961; the program’s proposed nuclear-powered aircraft, the Convair X-6, was never built.

Is It Possible to Build a Nuclear-Powered Aircraft? Surprisingly, Yes

The Air Force wanted nuclear propulsion because conventional strategic bombers were limited in range and endurance by their fuel. A nuclear-powered aircraft could theoretically remain aloft for much longer because its engine heat would be generated from fission rather than burning jet fuel. That would have meant incredible endurance, persistent nuclear patrols, less dependence on vulnerable forward air bases, and a bomber that could remain airborne while waiting for orders during a crisis, thereby equating to less lag time. As noted, this would have also guaranteed US second-strike capability in an era before reliable ICBMs or SLBMs, meaning that only air-delivered bombs were the only reliable arrow in America’s nuclear quiver.

Surprisingly, the technology for building the aircraft was not as far-fetched as one might think. In a normal jet engine, fuel is ignited inside the engine, raising the temperature of the air and causing it to expand. The expansion propels the air out of the back of the engine at a higher speed than it entered, giving the engine thrust. A nuclear-powered jet engine would rely on the nuclear reactor to heat the air instead of a combustion reaction, but the basic underlying principle would remain the same. For the project, the Air Force tested two different nuclear jet designs: a shielded reactor that transferred heat via a heat exchanger, and an unshielded reactor that heated the air directly. The former design was somewhat safer, but heavier and more costly; the latter was far simpler and cheaper, but had the side effect of producing highly radioactive exhaust.

Ultimately, the ANP program fell short of its goal, but it did yield an important achievement: the Aircraft Reactor Experiment (ARE). ARE was designed to prove that an aircraft reactor could combine high power density with very high operating temperatures. It produced up to 2.5 MW thermal and operated for 221 hours. These were impressive numbers, and the project was historically significant because it happened to be the first molten-salt reactor ever built and operated. Using molten fluoride salts with uranium fuel, the ARE safely reached temperatures as high as 860 degrees Celsius (1,580 degrees Fahrenheit).

It’s important to note that, though the program was canceled before the X-6 was ever flown, the US did fly a nuclear reactor. The Convair NB-36H Nuclear Test Aircraft, a modified B-36 Peacemaker bomber, served as the test platform; although it was conventionally powered, it proved that nuclear reactors could be made light enough for flight operations. Completing 47 missions over West Texas and southern New Mexico, the modified B-36 enjoyed relative longevity, too.

Why Did the Air Force Shut Down the ANP Program?

The program was shuttered for multiple reasons.

• First, the technology was difficult. Reactor weight, crew shielding, heat management, and aircraft complexity were all significant hurdles.
• Second, safety concerns mounted as the project continued. Air accidents, while rare, are a fact of life, and the 1950s had already seen several “broken arrow” incidents in which nuclear-armed bombers had crashed. A crash by a nuclear-powered aircraft would destroy the reactor and spew its contaminants into the environment, instantly creating a nuclear catastrophe far more serious than any nuclear accident up to that point in time.
• Third, the need for a nuclear-powered bomber was ultimately undone by the arrival of operational ICBMs starting in 1959. The ICBM was simple, reliable, and effective; it didn’t need pilots or radiation shielding or a giant airborne reactor.

Accordingly, John F. Kennedy killed the ANP program on March 26, 1961. In the 60-plus years since, no other nuclear-powered aircraft has ever been built. However, Russia recently developed a nuclear-powered cruise missile, the “Burevestnik,” based on the same principle of propulsion—and with the same radioactive environmental consequences!

About the Author: Harrison Kass

Harrison Kass is a writer and attorney focused on national security, technology, and political culture. His work has appeared in Tablet, City Journal, The Hill, The Spectator, and The Cipher Brief. He holds a JD from the University of Oregon and a master’s in Global & Joint Program Studies from NYU. More at harrisonkass.com.

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