Atomic Wings : A new mini-reactor revives the dream of a nuclear-powered aircraft
After more than six decades of research, the first atom-powered airplane is cleared for takeoff. Although details of the project remain classified, a description of this remarkable aircraft has begun to emerge from technical conferences and declassified engineering studies. The plane will be both familiar and unique. Familiar in that it will resemble a Northrop Grumman Global Hawk, the bulbous-nosed unmanned aerial vehicle (UAV) that the U.S. Air Force has used to track enemy movements in Afghanistan and Iraq. Unique because its nuclear reactor is unlike any other. Rather than split heavy elements or fuse light atoms–as in fission and fusion reactors–it will use what is known as a triggered isomer reaction. If this new powerplant, called a quantum nucleonic reactor, performs as scientists expect, its effect on the aircraft industry may prove as revolutionary as the introduction of the jet engine.
Ungainly Elegance
To the trained eye, the ungainly Global Hawk is a thing of beauty. A triumph of function over form, its whale-snout nose presents a tiny radar cross section. The thickly shrouded rear-mounted engine, located high in the tail, presents a minimal heat signature. Even the paint, which appears faded, serves a purpose: It helps dissipate heat from the plane’s electronic bay. Together, these design features make the Global Hawk virtually invisible as it loiters at 45,000 ft., directing its powerful radar and high-resolution cameras on trouble spots.
One improvement would make the Global Hawk the perfect surveillance platform: eliminating the need to top off its fuel tanks. For UAVs operating deep within hostile airspace, refueling requires dashing hundreds, sometimes thousands, of miles to a friendly landing field. It is chiefly for that reason that the Global Hawk has been selected as a testbed for one of the boldest experiments in aviation history. Project managers for Northrop Grumman and the U.S. Air Force Research Laboratory tell people they have begun discussions that could lead to the conversion of a Global Hawk to a nuclear-powered aircraft.
If the plan takes shape, a Global Hawk will be pulled off the production line and undergo extensive airframe and powerplant modifications. Chief among these will be the addition of some 2700 pounds of radiation shielding. Installed between the tail section and the main electronics bay, the shielding will create a “hot cell.” In this area, which will be designed to minimize leakage of radiation, engineers will install the world’s first airborne quantum nucleonic reactor.
A solar cell or engine-mounted generator sends electricity to run a small X-ray machine. The X-rays strike a block of hafnium-178, triggering a drop in the energy levels within the nucleus of the hafnium atoms. This change in energy levels is accompanied by the release of a burst of gamma radiation. The gamma rays heat the core of a heat exchanger. Superheated air from the exchanger floods into the jet engine, performing the same function as the expanding gases created by burning jet fuel. For safety reasons, conventional jet fuel will power the engine when it is below cruising altitude.
Flying Nukes
A jet engine is the essence of mechanical simplicity. Fuel and air are mixed, compressed and ignited. As the gas burns, it moves rapidly rearward, propelling the aircraft forward. Normally, this is done by burning jet fuel, which is exactly what the new nuclear plane will do when it takes off, climbs and lands. When it reaches cruising altitude–in the vicinity of 45,000 ft. and above trans-Atlantic airline traffic–the engine will switch over to running on hot air created by the reactor. Using this power source, an unmanned version could remain on station for months on end. A manned version, the logical next step, could operate as long as the crew had food.
Building a nuclear aircraft poses daunting engineering challenges. The underlying operating principle, however, is straightforward. In a fission reactor, atoms of a very heavy element, such as uranium, are persuaded to split apart, casting off neutrons that split other atoms and produce heat. In a fusion reactor, atoms of a very light element, such as hydrogen, are cajoled to join. Here, too, the conversion of mass into energy obeys the tenets of Einstein’s famous E=mc2 equation. The immense heat release keeps the reaction going.
Fusion reactors are in their infancy. But as early as 1940, scientists were thinking about ways of using the heat from nuclear fission to power airplanes. From the late 1950s through the 1980s, the Air Force and the Navy drew up blueprints and got as far as testing components for nuclear craft. At one point, a converted Convair B-36 Peacemaker flew with an operating reactor. However, none of these components were ever connected in the same airplane and a nuclear-powered aircraft never flew. The snag was the shielding needed to protect air crews from radiation–principally neutrons–streaming from the reactor. Planes with enough shielding to protect humans were too heavy to carry weapons. The quantum nucleonic reactor neither splits nor fuses atoms. Rather, it creates its power by triggering a massive release of gamma radiation. This is dangerous to humans, but requires less shielding to control.
Radical Reactor
The fuel for the quantum nucleonic reactor is a form–or isomer–of hafnium. Paradoxically, hafnium is the same element used to slow chain reactions in some fission reactors. A nuclear chain reaction occurs when neutrons emitted by a splitting atom strike an adjacent atom, causing it to split as well. Hafnium has a considerable capacity to absorb neutrons without splitting, hence its use as a brake or control rod in fission-type reactors.
In the late 1990s, researchers at the University of Texas in Dallas made a remarkable and unexpected discovery about the hafnium isomer known as hafnium-178. When they bombarded the metal with “soft” X-rays like those your dentist uses to examine your teeth, the metal released a burst of gamma rays 60 times more powerful than the X-rays. While this may seem impossible, it is permitted by the laws of physics. On the subatomic level, bombarding hafnium-178 with X-rays has an effect similar to triggering a small avalanche by tossing a snowball onto a snow-covered roof.
One of the most useful aspects of this newly discovered type of nuclear reaction is that the gamma ray output drops precipitously the moment power to the X-ray machine is turned off, explains Capt. Christopher Hamilton. He conducted research on a hafnium reactor at Wright-Patterson Air Force Base in Ohio, and was the first to propose using that device to power a Global Hawk.
A hafnium-fueled reactor has two other attractive features, Hamilton says. Since it produces only gamma radiation, less shielding is required. And should an accident occur, there is less of an environmental concern than with fission. Hafnium-178 has a half-life of only 31 years compared to thousands of years for other reactor fuels. In addition, unlike uranium or plutonium, hafnium-178 cannot support a chain reaction, which means it cannot be used to make rogue nuclear weapons.
In his report on the potential for the new reactor, Hamilton calculated that a small X-ray machine could be used to generate gamma radiation and create sufficient heat to run a conventional military jet engine. The Los Alamos and Sandia nuclear weapons laboratories in New Mexico have since taken up research for the project, supported by funding from the Department of Energy. Researchers involved with these projects have been instructed to discourage public discussion of the new type of reactor. Los Alamos scientists have expressed suspicion that the triggered isomer reaction process may not release useful amounts of heat. The Department of Defense, on the other hand, has put the reactor on its Militarily Critical Technologies List, which means it is on the fast track for future funding.
Executives for Northrop Grumman tell the press that while they have not yet signed a contract to convert a Global Hawk to nuclear power, they are aware of discussions taking place within the Air Force. Conventional aircraft can take a decade to move from concept to the runway. The civilian atomic airplane has, in one form or another, been under discussion for more than 60 years. With the emergence of a new type of power-plant, that decades-old dream may at long last take wing.
The quantum nucleonic reactor neither splits nor fuses atoms.
Hafium-178 has so low radiation levels, that its applications in passenger carrying aircrafts is being evaluated.
– Sourced from popular mechanics
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