Nuclear Energy and the First Law
Energy can be neither created nor destroyed, although it may be changed from one form into another. (First Law of Thermodynamics)
In this century, the First Law, and a similar law that states that mass can be neither created nor destroyed, have been modified a bit -- we now know that it is possible to change small amounts of mass into large amounts of energy and vice versa. In fact, we now recognize that this conversion of some of the tiny amount of the mass that holds atomic nuclei together into energy provides virtually all of the energy we use.
No, I don't mean that we have a hidden atomic power plant in every city. We have only a few plants that generate a small amount of energy by splitting heavy, unstable atoms such as uranium into two or more pieces. A small part of the mass, the part that held the unstable nucleus together, is released and turned to heat energy in the process, and that heat is then used to generate electricity.
Our main source of atomic power, the sun, is 93 million miles away, and operates by combining four hydrogen nuclei into a single nucleus of helium. In this case, the mass that binds the helium nucleus together is negative -- a helium nucleus weighs less than the four hydrogen atoms that formed it. The missing mass is released as energy -- energy which is eventually radiated from the surface of the sun as x-rays, ultraviolet light, visible light, infrared light, and radio waves. A tiny fraction of that solar energy reaches the earth, and that tiny fraction, converted to more familiar forms, provides us with almost all of the energy we use.
Water power? The sun's heat evaporated the water which later fell as rain on high ground. As the water runs downhill, some of the gravitational potential energy given to it by the sun's radiant energy can be extracted by human engineering and turned into mechanical energy and then into electrical energy.
Wind power? Winds are generated by the differential heating of the earth's surface by the sun. Cold air tries to flow under warmer, lighter air, and the earth's rotation twists this simple direct flow into the endless swirl of winds around our planet. A small part of the kinetic (motion) energy of the winds can be harnessed to pump water or generate electricity.
How about the wood, coal, and oil that provide the bulk of the energy we use? Certain wavelengths of the sun's radiation are absorbed by the chlorophyll in living plants, and this energy is stored in the chemical bonds of the carbohydrates making up most of the plants. This stored energy may be obtained directly by burning the plants (wood fires), or it may go to nourish an animal. A very small fraction of the mass of plants and animals that have died during the last few hundred million years has been buried without decaying, and the heat and pressure deep within the earth have changed some of the stored solar energy in their bodies into coal, oil, and gas. All of the fuels we burn obtained their energy originally from the sun.
A tiny fraction of our energy needs are met by direct use of solar radiation for heating. Direct transformation of solar radiation into electricity is also possible. If you've driven the Parks Highway you may have noticed that some of the more remote crossing lights on the Alaska Railroad are powered by batteries charged by solar cells.
Geothermal energy doesn't rely on the sun, but it is of nuclear origin. The same unstable heavy elements that drive nuclear power plants exist in minute quantities in almost all rocks. In addition to providing the radon that leaks into our basements, the slow breakdown of these elements produces the heat we tap for geothermal energy.
People disagree -- usually with good reasons on both sides -- on almost everything to do with nuclear energy. But we'd be in pretty sad shape without nuclear reactions, especially the ones in the sun.
