Science: Breeding Atoms

Experts called it the biggest atomic news since the end of World War II. The Atomic Energy Commission revealed last week that it is now considered practical to build a nuclear reactor which will “breed” more atomic fuel than it consumes.

Uranium is a tricky element. As it comes from the mines, it contains only .7% of the active isotope U-235, whose atoms “fission” (split in two) with a big release of energy. Nearly all the rest is 11-238, an idle isotope which will not fission naturally, though its heavy nucleus contains about the same energy as 11-235.

When natural uranium is put in a chain-reacting pile, its U-235 atoms start splitting and yielding energy, “fission products” and free neutrons. Some of the neutrons are needed to split more U-235 atoms and keep the reaction going. Others are absorbed by impurities or escape from the pile. The rest enter the atoms of U-238, ultimately turn them into plutonium.

Burn-Out. Plutonium is fissionable and a fine nuclear fuel, but the first reactors did not produce enough of it to replace the U-235 consumed. So their nuclear fuel gradually “burned out,” leaving U-238 as a sort of ash. Thus, the reactors of the early atomic age could utilize only a very small part of the uranium fed into them.

The AEC’s new breeders, or converters, will lessen the waste, presumably by causing more neutrons to be absorbed byU-238. If the amount of plutonium or other nuclear fuel thus produced is larger than the U-235 consumed, the pile could continue in operation for a very long time. First the original U-235 would be consumed, yielding energy and plutonium made out of 11-238. Then some of the plutonium would fission, yielding energy and creating more atomic fuel. Theoretically, the process might continue until all the 11-238 is consumed. Natural uranium could yield something like 140 times as much energy as it would if only its U-235 were utilized.

No Ashes. The AEC does not claim immediate 100% efficiency. The accumulation of radioactive fission products as impurities in the uranium, for instance, will certainly cause trouble long before the action is complete. But the contaminated uranium could be purified and “recycled.” The AEC did not say so, but there is a possibility that when the breeding process has been refined, the uranium can be run through the reactor again & again until essentially all of it has been turned into energy. The world might thus have a practically inexhaustible source of nuclear fuel.

Although the AEC emphasized the peaceful aspects of its new process, the military aspects are important too. Fissionable material, however obtained, can be burned in a peaceful reactor or detonated in a bomb. If the new converter works as well as expected, it will help the U.S. make more bombs out of less uranium.

The commission is sure the converter will work. The theoretical calculations are complete; the engineering designs are almost complete. No fuel has been bred so far because the reaction will not work except in a full-scale plant. A $3,500,000 plant will soon be built at Arco, Idaho.