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. [Illustration: _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._] [Illustration: _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]