Nuclear Reactors
The development of the nuclear chain reaction was not in the direction of bombs only. Nuclear reactors designed for the controlled production of useful energy multiplied in number and in efficiency since Fermi’s first “pile”. Many nations now possess them, and they are used for a variety of purposes.[2]
The USS Nautilus, the world’s first nuclear powered submarine, in New York harbor.
In 1954 the first nuclear submarine the USS Nautilus was launched by the United States. Its power was obtained entirely from a nuclear reactor, and it was not necessary for it to rise to the surface at short intervals in order to recharge its batteries. Nuclear submarines have crossed the Arctic Ocean under the ice cover, and have circumnavigated the globe without surfacing.
In 1959 both the Soviet Union and the United States launched nuclear-powered surface vessels. The Soviet ship was the icebreaker, Lenin, and the American ship was a merchant vessel, the NS Savannah.
In the 1950s nuclear reactors were also used as the source of power for the production of electricity for civilian use. The Soviet Union built a small station of this sort in 1954, which had a capacity of 5,000 kilowatts. The British built one of 92,000 kilowatt capacity, which they called Calder Hall. The first American nuclear reactor for civilian use began operation at Shippingport, Pennsylvania, in 1958. It was the first really full-scale civilian nuclear power plant in the world.
The world appeared to have far greater sources of energy than had been expected. The “fossil fuels”—coal, oil and natural gas—were being used at such a rate that many speculated that the gas and oil would be gone in decades and the coal in centuries. Was it possible that uranium might now serve as a new source that would last indefinitely?
It was rather disappointing that it was uranium-235 which underwent fission, because that isotope made up only 0.7% of the uranium that existed. If uranium-235 were all we had and all we ever could have, the energy supply of the world would still be rather too limited.
There were other possible “nuclear fuels”, however. There was plutonium-239, which would also fission under neutron bombardment. It had an ordinary half-life (for a radioactive change in which it gave off alpha particles) of 24,300 years, which is long enough to make it easy to handle.
But how can plutonium-239 be formed in sufficient quantities to be useful? After all, it doesn’t occur in nature. Surprisingly, that turned out to be easy. Uranium-238 atoms will absorb many of the neutrons that are constantly leaking out of the reactor and will become first neptunium-239 and then plutonium-239. The plutonium, being a different element from the uranium, can be separated from uranium and obtained in useful quantities.
Such a device is called a “breeder reactor” because it breeds fuel. Indeed, it can be so designed to produce more plutonium-239 than the uranium-235 it uses up, so that you actually end up with more nuclear fuel than you started with. In this way, all the uranium on earth (and not just uranium-235) can be considered potential nuclear fuel.
The Shippingport Atomic Power Station, the first full-scale, nuclear-electric station built exclusively for civilian needs, provides electricity for the homes and factories of the greater Pittsburgh area. The pressurized-water reactor, which now has a 90,000-net-electrical-kilowatt capacity, began commercial operation in 1957. The reactor is in the large building in the center.
The lights of downtown Pittsburgh.
The first breeder reactor was completed at Arco, Idaho, in August 1951, and on December 20 produced the very first electricity on earth to come from nuclear power. Nevertheless, breeder reactors for commercial use are still a matter for the future.[3]
Another isotope capable of fissioning under neutron bombardment is uranium-233. It does not occur in nature, but was formed in the laboratory by Seaborg and others in 1942. It has a half-life of 162,000 years. It can be formed from naturally occurring thorium-232. Thorium-232 will absorb a neutron to become thorium-233. Then 2 beta particles are given off so that the thorium-233 becomes first protactinium-233 and then uranium-233.
If a thorium shell surrounds a nuclear reactor, fissionable uranium-233 is formed within it and is easily separated from the thorium. In this way, thorium is also added to the list of earth’s potential nuclear fuels.[4]
If all the uranium and thorium in the earth’s crust (including the thin scattering of those elements through granite, for instance) were available for use, we might get up to 100 times as much energy from it as from all the coal and oil on the planet. Unfortunately, it is very unlikely that we will ever be able to make use of all the uranium and thorium. It is widely and thinly spread through the crustal rocks and much of it could not be extracted without using up more energy than would be supplied by it once isolated.
Another problem rests with the nature of the fission reaction. When the uranium-235 nucleus (or plutonium-239 or uranium-233) undergoes fission, it breaks up into any of a large number of middle-sized nuclei that are radioactive—much more intensely radioactive than the original fuel. (It was from among these “fission products” that isotopes of element 61 were first obtained in 1945. Coming from the nuclear fire, it reminded its discoverers of Prometheus, who stole fire from the sun in the Greek myths, and so it was called “promethium”.)
The fission products still contain energy and some of them can be used in lightweight “nuclear batteries”. Such nuclear batteries were first built in 1954. Some batteries, using plutonium-238 rather than fission products, have been put to use in powering artificial satellites over long periods.
Unfortunately, only a small proportion of the fission products can be put to profitable use. Most must be disposed of. They are dangerous because the radiations they give off are deadly and cannot be detected by the ordinary senses. They are very difficult to dispose of safely, and they must not be allowed to get into the environment, especially since some of them remain dangerous for decades or even centuries.
The Experimental Breeder Reactor No. 2 building complex in Idaho. The reactor is in the dome-shaped structure.