Science: Atomic Furnace

Talk of atomic power for peaceful purposes is usually treated only as a hope for the distant, peaceful future. At last week’s Chicago meeting of the American Chemical Society, Atomic Energy Commissioner Eugene M. Zuckert had better news. Said Zuckert: “Scientists had thought of atomic power as being economically practical ten or 15 years hence. We suddenly find that power from atomic energy seems closer at hand . . . Even in the six months I have been with the commission there is a noticeable quickening of interest in atomic energy.”

Most estimates of the cost of atomic power, said Zuckert, have been based on the amount of plutonium that is produced, along with energy, when Uranium-235 is “burned” in a reactor. The operation can be made profitable for a power company if the Government will buy the plutonium at a high enough price and stockpile it for atomic weapons. Now, said Zuckert, “we may hit upon the development of power at competitive cost from non-plutonium-producing reactors . . . The strides that engineers and scientists are making are so great that ‘power only’ reactors may be nearer than we dare hope for.”

Core & Blanket. Zuckert did not explain what he meant by a “power only” reactor, but in the current issue of Nucleonics, Dr. W. H. Zinn, director of the AEC’s Argonne National Laboratory, described the experimental “breeder” reactor built and operated by the University of Chicago at Arco, Idaho. It produces “power only” by burning its own byproduct, plutonium.

The active core of the Arco breeder is about the size of a football. It is made of “enriched uranium,” i.e., uranium rich in fissionable 11-235. Around the core is a “fertile blanket” of 11-238, the spent metal that remains when U-235 is extracted from natural uranium to make atom bombs. Through both blanket and core circulates a sodium-potassium alloy that is liquid at ordinary temperatures. This coolant carries away the heat of the nuclear reaction. The fluid metal leaves the reactor at 660° F., and produces enough steam to generate 250 kw. of power.

More important is what happens in the blanket of U-238. The fissioning U-235 in the core sends out a dense flux of highspeed neutrons. They are absorbed by the blanket, turning some of its U-238 into plutonium. Since this is also fissionable, it can be extracted chemically and used as fuel in the heat-giving core.

Burning Plutonium. The purpose of the Arco breeder is to “breed” more plutonium than is needed to replace the U-235 that it consumes. Dr. Zinn did not say so directly, but his and Commissioner Zuckert’s optimism suggests that it can be done. If so, the “power only” reactors of the future can burn all of their uranium, not merely the .7% that is naturally fissionable. There will be no need for the Government to buy their plutonium; it will be burned too. If uranium gets scarce, the “fertile blanket” can be made of thorium, which neutrons turn into fissionable U-233-Dr. Zinn did not give the cost of natural uranium, but he estimated that if it cost $35 a Ib. (probably a generous figure), the fuel cost of the power produced from it would be only .0013¢ a kilowatt-hour. The fuel cost of electricity from coal is about .35¢ a kilowatt-hour—nearly 300 times as much.