More than 50 years ago, aerospace engineers spent over $1 billion—in 1950s money—designing atomic-powered airplanes in the hope that such superfast jets could remain aloft for 15,000 miles (21,150 kilometers) at a time. They expected one pound (half a kilogram) of nuclear material would eliminate the need for refueling stops. An intriguing concept, but nuclear aircraft were grounded before the end of the Cold War due to, among other things, concerns about passenger and crew exposure to radiation. As airlines grapple with the high cost of petroleum and the growing demand for a cleaner form of fuel, might it be time to take another look at nuclear?



Between 1946 and 1961 the U.S. Air Force and the now-defunct Atomic Energy Commission (whose regulatory duties were taken over by the Nuclear Regulatory Commission, or NRC in 1975) oversaw the Aircraft Nuclear Propulsion (ANP) program. But ANP engineers and management were mired in debate over reactor technologies, how best to transfer nuclear power to a conventional engine, and the best material to shield the crew from radiation. Ultimately, they retrofitted the Convair B-36, a hybrid prop/jet-engine bomber weighing more than 400,000 pounds* (181,435 kilograms) and with a wingspan of 230 feet (70 meters), to house an air-cooled reactor in the aft bomb bay. Up front, the plane was outfitted with a 12-ton lead-and-rubber-shielded crew compartment. The atomic version of Convair's plane, called "Peacemaker," made 47 test flights over Texas and New Mexico between July 1955 and March 1957.



But by the end of the decade, advances in conventional aircraft and engine design outmoded the atom-powered B-36 and the public became concerned about the dangers of a nuclear reactor flying overhead. The program also failed to yield a commercial aircraft due to its steep cost (hundreds of millions in today's dollars, says Stephen Schwartz, editor of The Non Proliferation Review, published by California's Monterey Institute of International Studies), prompting Pres. John F. Kennedy to cancel the ANP in 1961. The U.S. government promptly redirected much of the project's resources toward space exploration and the race with the Soviet Union to reach the moon.



Recently, however, the search for cleaner fuels has once again raised the specter of such airships. Ian Poll, professor of aerospace engineering at the Cranfield University in England, in a recent lecture covered by the Times of London called for a "big research program to help the aviation industry convert from fossil fuels to nuclear energy." Poll, head of technology for the British government–funded Omega Project, a division of Manchester Metropolitan University that partners with industry to study the environmental impact of aviation and offer possible solutions, pointed out the need for nonkerosene-powered aircraft



"I think nuclear-powered airplanes are the answer beyond 2050," he said, concluding, "If we want to continue to enjoy the benefits of air travel without hindrance from environmental concerns, we need to explore nuclear power. If aviation remains wedded to fossil fuels, it will run into serious trouble."



Sharing the friendly skies with a nuclear reactor is probably enough to keep even the most seasoned travelers awake throughout an overnight flight, but nuclear power would have a few advantages. In addition to not needing to refuel between flights, a nuclear-powered airplane in theory would not pollute the environment as long as the radioactive waste from its reactor could be contained (the Air Force's project never progressed far enough to come up with a practical way to address this).



Nuclear reactors are routinely used by the U.S. Navy to power its aircraft carriers and submarines. The U.S. commissioned the first of its nuclear sub fleet, the USS Nautilus, in 1954, and continues to rely on them today as part of its nuclear war deterrent. The U.S.S.R. reportedly built 245 nuclear subs during the Cold War, according to the Monterey Institute of International Studies's Center for Nonproliferation Studies.



Poll proposes nuclear-powered airplanes using reactors with engines on the wings. "The risk of reactors cracking open in a crash could be reduced by jettisoning them before impact and bringing them down with parachutes," he told the Times of London, adding that, in the worst-case scenario, if the armor plating around the reactor was pierced "there would be a risk of radioactive contamination over a few square miles." Poll declined to be interviewed for this article.



But many nuclear physicists and engineers are not on board with nuclear airplanes, especially in the aftermath of the September 11, 2001, attacks during which terrorists plowed jumbo jets into the World Trade Center and Pentagon. "We've been worried since 9/11 about how to protect against bad guys hijacking an aircraft and crashing it into a nuclear power plant upwind of a heavily populated area," says David Lochbaum, director of the Union of Concerned Scientists's Nuclear Safety Project, a group that monitors the performance of nuclear plants and the NRC, which regulates them. "Let's now put the nuclear reactor in the plane itself, so they can target big cities without a nuclear plant upwind," he adds, with sarcasm. "What a Christmas present for the terrorists of the world."



Lochbaum worries that terrorists could hijack and use jets as nuclear missiles or take them apart for materials to build their own so-called dirty bombs.



No matter how well shielded, crew and passengers would still run a high risk of exposure to radiation (on top of cosmic radiation that all travelers are exposed to simply from taking to the skies). What's more, the planes would have to be so large—about twice the size of a 747—that airports would have to build special docking stations apart from their existing terminals.



Nuclear planes are "not good for anybody," says Theodore Rockwell, founder of Radiation, Science & Health, Inc., a non-profit organization in Chevy Chase, Md., that advocates for objective review of low-level radiation science policies. During World War II, Rockwell worked a program at the U.S. Department of Energy's Oak Ridge National Laboratory, where he helped develop new materials and designs for radiation shielding. Although a supporter of nuclear power, he draws the line at using it to fuel aircraft.



In addition to the potential passenger dangers, he says that pilots could only fly a limited number of flights to prevent overexposure to nuclear radiation, noting that after a few flights, they would have been exposed to far more radiation than nuclear power plant workers. "Power has to be predicable to be useful," he says, "and nuclear is by far easiest to predict on Earth."



A more promising green fossil-fuel alternative is biofuel. Richard Altman, executive director of the Commercial Aviation Alternative Fuels Initiative (CAAFI), a consortium sponsored by the FAA that promotes the move away from petroleum-based jet fuel. CAAFI favors "drop-in" fuels that work within existing infrastructures—that is, they are interchangeable with fossil fuels and require no alterations to aircraft or airports. These alternatives include liquids from both renewable (plants) and nonrenewable (coal and natural gas) sources that are better than an oil refinery on a greenhouse gas (GHG) life-cycle basis. They have the same safety and density as fossil fuels, Altman says, and would not alter planes’ performance, range, or capacity to carry passengers.

*Note (12/5/08): The weight given for the B-36 was corrected after publication of this article.