National Geographic : 1954 Jan
Man's New Servant, the Friendly Atom change the U238 into plutonium, a man-made element, which is fissionable like U235. This plutonium then enters into the chain reaction; its atoms are split by neutrons, releasing both energy and more neutrons. Some of these neutrons change still more uranium 238 into plutonium, which releases still more energy and neutrons; and so on. The breeder reactor is the kind which prob ably will be used eventually in making elec tric power because it can utilize the abundant supplies of uranium 238 as well as the scarcer uranium 235. An experimental breeder re actor already has been operated in Idaho for more than two years, producing all the elec tricity needed to supply light and power for the building in which it is housed. Actually, the breeding is not quite as simple as it sounds. The newly created plutonium fuel must be separated from U238 before it can be used to fuel another reactor, and a breeder may have to run several years before it yields as much new fuel as was put in originally. Uranium to Power Atomic Submarine The first practical use of atomic energy to manufacture power will be to drive the Navy's two new submarines, Nautilus and Sea Wolf. The "firebox" of the Nautilus's engine will be a reactor in which the fissioning of uranium atoms creates great quantities of heat. This type of reactor is much smaller than the big ones used in making radioisotopes and is of different design. Water, circulating through the reactor, will absorb the heat and carry it out to a boiler to heat more water and make steam. The steam will operate turbines, which will turn the propeller shafts. Nautilus will be the world's first true sub marine, a craft which can operate deeply sub merged for months at a time if necessary, with out ever having to come to the surface. This is possible because no oxygen is needed for the production of atomic energy. A few pounds of uranium will run an atomic submarine for months without refueling. Her range of operation will be limited not by her fuel supply but only by the crew's endurance and the supplies of bottled oxygen, food, and weapons she can carry. In a recent test, 23 members of a crew stayed below battened hatches for two months in a submarine along side the dock at Groton, Connecticut. They suffered no serious ill effects. Running a submarine by atomic power has created special problems. Since the water that circulates through the reactor and boiler will become radioactive, pipes, valves, and pumps must be absolutely tight, and strong enough to withstand even the shock of depth charges exploding near by. A leak of radioactive water would endanger the crews' lives. The reactor itself must be heavily shielded by thick concrete, lead, or some similar material, to protect the crew from deadly radiation. Sea Wolf Will Use Liquid Metal U. S. S. Sea Wolf, the second atomic sub marine, will be powered by a slightly different type of reactor, using liquid sodium metal in stead of water to carry heat from the reactor to the boiler. To make Nautilus's atomic submarine en gine work successfully, scientists had to find a way to produce in quantity a metal which was little more than a laboratory curiosity only a few years ago. This is zirconium, long known but little used because it was difficult to produce in pure form. Most metals, if used in construction of cer tain types of atomic reactors, absorb so many neutrons that the chain reaction is badly slowed down. But zirconium absorbs very few neutrons and is also highly resistant to corrosion. Under the lash of urgent necessity, scientists developed methods of producing pure zirconium at much lower costs and in large quantities. Five years ago the entire world supply could be set on an ordinary table. Today we are producing about 300,000 pounds a year. Driving airplanes with atomic power is being studied, but is a far more difficult prob lem. Such planes would use nuclear energy simply as another way of supplying heat, in stead of burning gasoline or jet fuel.* For propeller-driven aircraft, the atomic heat would be used to make steam or hot air for driving turbines, which would turn the "props." In atomic-powered jet planes, small reactors probably would heat the air that is compressed and released in the jets. Chief difficulty in designing atomic-powered planes is that the intense radioactivity from the engines would be highly dangerous to the crew unless they were protected by some very dense shielding material, such as concrete or lead. The weight would be a serious handi cap in a plane. Ground crews, too, would be * See, in the NATIONAL GEOGRAPHIC MAGAZINE: "Fact Finding for Tomorrow's Planes," by Hugh L. Dryden, December, 1953, and "Flying in the 'Blow torch' Era," by Frederick G. Vosburgh, September, 1950.