Conventional power sources produce electricity by creating steam to power a turbine. The turbine is attached to an electrical generator which creates electricity. The heat that turns water into steam in most plants is created by burning fossil fuel. In the United States the fossil fuel is usually coal or natural gas. In some countries, such as Japan, oil is more frequently used.
In a nuclear power plant, the heat that turns water into steam is generated by a nuclear reactor, where natural radiation from nuclear fuel creates heat. The heat produced in nuclear reactors can also be used for purposes other than generating electricity, such as propelling ships and submarines in our navy, giving them extensive range without refueling. More than 200 such ships have been built.
Background Nuclear Physics
To see how a nuclear reactor generates heat, we must review some elementary physics. The smallest entity of a chemically homogenous substance that still has the same physical and chemical properties as the substance in bulk is called a molecule. In all but a handful of cases, a molecule is a combination of atoms, of which there are 92 occurring naturally on the planet, which we call elements. Nearly two dozen additional elements have also been created by scientists in laboratories.
The lightest atom is hydrogen, the heaviest is uranium. Each atom consists of a positively charged nucleus and a shell of negatively charged electrons which in artists’ conceptions are usually depicted as a little solar system.
The nucleus of an atom is much heavier than its electron shells, but the negative electric charge of the electron shell, in a stable atom, just equals the positive charge of the nucleus, so the two charges cancel out and the atom is electrically neutral. The number of electrons, which is the same as the number of protons in the nucleus, is called the atomic number. Hydrogen, with one proton in the nucleus and a single electron in orbit, has an atomic number of one. Uranium has 92 of each and thus an atomic number of 92.
It is this atomic number that determines the chemical and most physical properties of the element.
Some elements may have different numbers of electrically neutral neutrons in their nuclei, giving them added weight though still the same electrical properties. These different forms are called isotopes. One isotope of hydrogen, for example, has two neutrons rather than one, and is called deuterium. When deuterium is combined with oxygen it forms heavy water. Another isotope of oxygen has three neutrons and is called tritium. Other isotopes are just designated by the number of protons and neutrons, such as Carbon 12, Carbon 13, and Carbon 14, with 6, 7, and 8 neutrons, respectively to go with the 6 protons.
When an isotope radiates atomic particles naturally, it is said to be fissionable. The only naturally occurring element that is fissionable and found in large quantities on the earth is Uranium 235 (92 protons and 143 neutrons). An atomic bomb is made of Uranium 235 or plutonium, which is a manufactured fissionable element.
In a uranium bomb, the material must be purified or enriched at great cost to more than 90 percent Uranium 235, because in natural uranium ore almost all the uranium is Uranium 238, which is not fissionable. Uranium ore is only about 0.7 percent fissionable U 235, and this small fraction must be increased to more than 90 percent to begin to make a bomb.
Even then, a small amount of nearly pure Uranium 235 will not create a chain reaction, which is the signature of an atomic bomb, because neutrons shooting out of the nuclei after each splitting or fissioning will simply leave the uranium instead of hitting other uranium nuclei, which is what creates a chain reaction.
To get a multiplicative chain reaction, the average number of neutrons absorbed by other nuclei per fission of a nucleus must be greater than one. There must therefore be enough of the material in the form of a sphere to ensure most of the liberated neutrons will strike other nuclei before they escape from the volume of uranium.
If the sphere of nearly pure Uranium 235 can be held together long enough for the chain reaction to take place rather than blow itself quickly apart, a nuclear explosion will take place. In a bomb, this is achieved by joining two pieces of uranium (or plutonium) of sub-critical size into a sphere of critical size, generally by firing them against each other with the assistance of an explosive. Obviously, this is a very complex process.
Nuclear Power Lacks Explosiveness
The uranium fuel used in power plants contains not 90 percent of Uranium 235, but only 3.5 percent, which of course is well below the critical minimum for an explosive nuclear reaction. Even in a runaway reactor, 100 fissions would cause no more than 101 fissions in the next generation. More importantly, the time elapsed between fissions of one generation and the next is about 100,000 times longer than in a nuclear explosion.
Simply put, inducing a nuclear explosion in 3.5 percent enriched uranium is absolutely impossible. It would defy the laws of nature. A nuclear power plant cannot produce a nuclear explosion.
Jay Lehr, PhD. ([email protected]) is science director of The Heartland Institute.