The matter in an atom is all energy, as Einstein indicated in 1905 with his famous formula E = mc2. Scientists have now learned to release about one thousandth of this energy by the process of nuclear fission, and as much as a hundredth by nuclear fusion. Even these small fractions are millions of times greater than those released in chemical combustion by fire, which taps only the external reaches of the atom.
In a nuclear chain reaction, explosion of a complex and unstable nucleus such as that of uranium releases neutrons which, when slowed down by colliding with other atoms (such as carbon or deuterium) used as "moderators," react with the nuclei of neighboring explosive atoms to cause them to rearrange into new patterns and release still further showers of neutrons. A pound of U 235, the isotope of uranium which, when separated from ordinary uranium, was first found able to support a nuclear chain reaction, can thus be made to release as much energy as 3 million pounds of coal gives when burned. But only one atom out of 139 of mined uranium consists of this isotope. This scarcity is offset by the fact that U 238, a more plentiful isotope, can be converted into plutonium atoms by bombarding its atoms with neutrons, and the newly produced atoms can then be used as nuclear fuel. The development of the breeder pile, which produces this nuclear fuel, has greatly increased our visible energy stores. The operator of a breeder pile is somewhat in the position of a householder who shovels coal and ashes in to his furnace, heats his house adequately, and then shovels out, instead of ashes, tons of coke that he can sell to the neighbors.
If it were not for the dangerous radiations produced by its activity, a nuclear reactor could be rather light. As it is, heavy shields are needed to protect its operators from radiations which, besides being directly damaging to living cells, produce lethal rays when they strike sand or air or any other surrounding material. Nearby innocuous atoms may be converted into unstable atoms, many of which are likely to explode and emit more rays at some future time. The automobiles powered by "pea‑sized plutonium engines" predicted by some journalists have lost much of their appeal because of the necessity of placing a concrete shield several feet thick under the driver's seat, and of providing heavy concrete fenders to protect the passers‑by.
Any nuclear reactor must be carefully supervised in its operation, because of the dangers of contamination from waste products that might escape after an accident. This dampens our enthusiasm for nuclear‑driven locomotives. Mopping up contaminated wreckage is a tedious and, if care is not taken, a dangerous job; and it is not always feasible.
Literally hundreds of different types of nuclear reactors have been designed, and these will soon evolve into as great variety as have ordinary engine‑driven vehicles, which are differentiating into thousand forms from tractors to helicopters. Airplanes driven by nuclear power seem practicable if the shielding problem for personnel can be solved, as by putting the power plant in a tractor plane, and the pilots and passengers into one or more gliders far enough behind to escape dangerous rays. Ships are already being driven by nuclear power, though their ability to carry enough stored energy to propel them for life will be limited by the need for occasionally sifting out nuclear ash from the fuel. Nuclear fuel can already compete in cost with oil for driving ships, but the first cost of a nuclear power plant is still much greater than that of an oil-burning power station.
Reactors to produce electric power from nuclear fuels are now being built both here and abroad, and some soon to be designed should give enough power to fill the needs of the largest city. All of the electrical power now used in the United States could in theory be produced from 60 tons of uranium. Though this nuclear fuel would last for many years, it would need repurification occasionally when it became too full of spent nuclei. Reactors for producing electric power now being built in England are expected to save 20 million tons of coal a year.
Nuclear power can already compete with domestic power costs for fuel and upkeep where these are above 2 cents a kilowatt‑hour wholesale, but the first cost and carrying charges are still too high. In Europe, where anything approaching a cent per kilowatt‑hour can compete, the price of uranium need only be cut in half to make it a commercial success as a fuel for power. Though it is unlikely to put the coal or oil industries out of business, it should by 1975 compete with them strongly in large power operations, especially in regions far from marine transportation.
There is a great deal of uranium in the world. Some living cells tend to concentrate it, and it is likely to be found with coal. Though sea water contains only 2.5 parts per billion of uranium, one ton of the granite of the hills could give the energy of 50 tons of coal once its content of these atoms was separated out.
A few years ago, when only uranium atoms of the U 235 isotope seemed fit for industrial energy release, the nuclear fuel in sight was equivalent to about 600 billion tons of coal, or one sixth of the world's reserves of fuel. The breeder pile, however, has raised visible nuclear energy reserves to the equivalent of 90 trillion tons of coal, and our visible energy store of all kinds is increased perhaps 25-fold over what could be seen a few years ago. Thus man is given extra ability either to destroy himself or to build more stately mansions for his soul.
Basking in the sunshine on a bright June day, we are not likely to think of our sun as the stabilized H‑bomb that it is. If all the light and heat radiated by this hydrogen reactor were focused on the earth, it would vaporize the oceans and shrivel our planet in a matter of seconds. At the center of the sun, at temperatures like those in the center of an A‑bomb, the nuclei of hydrogen atoms fuse into helium nuclei, thus converting about one per cent of the matter in each nucleus into energy ‑just enough to keep the earth comfortably warm.
The sunlight that falls on a single acre of the welcoming earth contains enough energy to keep a thousand people healthy, active, and comfortable. Instead of doing this, most of it is wasted, and the remainder now serves only one or two persons. A 16‑mile‑square area in any desert receives enough sunshine to satisfy all the energy needs of the American people today. Someone has calculated that the sun gives the earth every three days as much energy as would be released by burning all the forests and all the coal and oil and gas in the world.
Thus there is lots of solar energy, and it appears to be free to anyone who wishes to scoop it up. But anyone who tries is likely to become disheartened by the many ways in which sunshine eludes his grasp, and is missing when he needs it most. The sun is overhead only part of the time. To light a city at night, solar energy should be held for at least twelve hours. To heat houses, it should be stored for days or months. We lack a cheap and efficient method of storing energy in quantity. In the photosynthesis on which all life depends, nature has developed a storage system that will hold energy for years in plant cells, but this operates at too low an efficiency to compete with the coal and oil that took thousands of times longer to produce than it does to burn. Fuel alcohol from potatoes or other crops, one of the best methods of storing solar energy, now costs four or five times as much as gasoline to produce.
Seventy‑four hundred horsepower flow continuously into the top of the atmosphere above each acre of land or sea facing the sun; but absorption and scattering by the molecules of the air and the inclination of the earth's axis in the latitude of New York reduce this to less than 4000 horsepower by the time it reaches the ground. Cloudy weather cuts it further to a yearly average of about 800 horsepower per acre. This is still a great deal of energy, but unfortunately storing it, carrying it to where it is to be used, and transforming it into the chemical, electrical, mechanical, and thermal forms we want for industry are likely to waste more than 85 per cent of the remainder, or to require setting tip installations which are too expensive to be practical. Some of the losses arise from immutable laws of nature, but others can be avoided by ingenuity and scientific acumen, and therein lies great hope for the future.