The possibility of catastrophic nuclear power-plant "accidents" isn't the only reason why we and many other scientists are apprehensive about the spread of nuclear power. Perhaps an even greater danger exists in the radioactive wastes produced within the power generators themselves. Until a means of safely disposing of these materials is found, the production of "no risk" nuclear-generated electricity will be impossible.
Remember that most reactors split uranium 235 (U-235) nuclei to produce heat energy. That heat provides steam, which in turn spins generator turbines. However, when the uranium atoms split they create fragments (called "fission products"), and the nuclear waste disposal problem begins. The fragments, for example, contaminate the reactor's fuel rods so badly that the rods must be replaced about once a year. (This replacement is necessary because the fission products "poison" the chain reaction by absorbing neutrons without fissioning. The trapped neutrons are then unable to sustain the "atomic" reaction.)
Furthermore, because many of these fragments remain highly radioactive after they're formed, the fuel rods (in which most of the fragments become embedded) are also radioactively "hot" by the time they're removed from the reactors. These used rods, in fact, are so radioactive that they're normally stored at the power plants for a period of several months until some of their most dangerous contaminants have had a chance to decay into somewhat less harmful materials.
The spontaneous changes in nuclei that result in the emission of radioactivity, you see, always transform an atom into something else. If its chemical properties are altered, the atom becomes another element. On the other hand, if an atom's nucleus is changed but its chemical properties remain the same, a different isotope of the same element is formed.
Uranium 235, for example, decays in a long series of steps that include the radioactive isotopes radium 226, radon 222, and polonium 218. The end result, finally, is the chemically stable, non-"hot" element lead 206.
The process of this breakdown is statistically predictable, even though the instant at which a single nucleus will be spontaneously transformed isn't. For this reason, atomic decay is measured in "half-lives," which indicate the time needed for one-half of the billions of atoms in a small quantity of material to undergo this transformation.
Let's take an example: One of the major short-lived isotopes in used nuclear fuel elements—iodine 131—has a half-life of 8.1 days. This means that, when 8.1 days have passed from any given time, half of the iodine 131 will be gone. After 16.2 days, only a quarter of the original quantity of isotope will be left; only one-eighth after 24.3 days; and so on. A period of 20 half-lives (which is less than six months in the case of iodine 131) will reduce the original radioactive isotope to one millionth of its initial mass.
You can see, then, that if all fission products had half-lives of about a week, the storage of these wastes wouldn't present much of a problem. They could simply be held at powerplant sites for a year or so, and could then be disposed of in any way suitable to their chemical characteristics. Residual radioactivity would by that time be practically nonexistent.
Unfortunately, however, many of the fission products regularly produced in nuclear reactors have extremely long half-lives. Those of strontium 90 and cesium 137 are 28 and 30 years respectively — which means that these isotopes would have to be stored for 1,000 years before their radioactivity could be safely ignored. And plutonium 239, which is formed in reactors by the non-fission absorption of neutrons into uranium 238, has a half-life of 24,400 years. This material, in short, should be kept out of the environment for at least one-half million years ... which is something on the order of 100 times longer than the human race has been recording its history!
The magnitude of our radioactive waste problem was made clear in a 1974 study by the now-defunct Atomic Energy Commission. The AEC calculated the amount of hot waste it expected would accumulate in the United States by the year 2000. Then the commission figured out how much air would be needed to dilute these materials to the so-called "maximum permissible concentration," or MPC. (At the MPC an individual who breathed the waste-polluted air would receive no more than four times the average exposure caused by natural radiation sources.)
And the AEC discovered that—by 2000 A.D.—the amount of air required to safely dilute the United States' inventory of atomic wastes would be 7,300,000,000,000 cubic kilometers ... approximately 1,750,000,000,000 cubic miles. This number represents a block of air 12,000 miles on a side: a mass large enough to cover the entire planet to a depth of 4,000 miles!
And one hundred years after that, 456,000,000,000 cubic miles would still be necessary. Add one thousand years, and the figure is still 36,000,000,000 cubic miles. And even a million years later (1,002,000 A.D), approximately a billion cubic miles of air would still be necessary to reach the MPC.
Remember, too, that these incredible volumes of atmosphere would only serve to dilute the radiation that still remained in wastes that the AEC expected to have accumulated by the year 2000. The figures don't even take into consideration any wastes that might be produced after that cutoff date!
The staggering size of these numbers helps to drive home the magnitude of our nation's nuclear waste disposal problem. Still, there are those in the government/industry/nuclear establishment who would prefer that the public didn't understand how overwhelming this problem actually is.
General Electric, for example, states reassuringly that the annual wastes produced by a nuclear power plant are equivalent in size to about one aspirin tablet for every person served by the installation.
This statement is a two-dimensional lie. In the first place, University of California physicist John P. Holdren has calculated (using AEC data) that "high level" wastes—in their most concentrated form—actually amount to a mass the size of about ten aspirins for every person served.
And those high level wastes are only the most radioactive residues of the fuel. There is an additional five tablets' worth of waste per person in the form of the intensely radioactive remains of the alloy tubes that held the fuel. Furthermore, intermediate-level and low-level wastes—which contain some very dangerous and long-lived isotopes—amount to well over 3,000 of those aspirin-tablet-sized portions of deadly material per person each and every year.
And this "understatement" of the volume of radioactive wastes (by a factor of more than 3,000) is actually the less dangerous side of General Electric's lie. The company committed an even more serious deception when it placed emphasis on the amount of the radioactive materials, rather than on the extremely high toxicity of these wastes. As Professor Holdren put it, "If a tablet were to be an apt comparison, it would have to be a cyanide tablet. And even that would not do justice to the actual toxicity of the fission products." (As a matter of fact, one-year-old radioactive waste is at least 100 times more toxic, by volume, than cyanide.)
We look forward to the day when the nuclear industry will be honest enough to announce that "The wastes produced annually by a nuclear power plant are equivalent in size to only several hundred cyanide tablets per person served." But even that unlikely candor would be misleading, because cyanide can be easily detoxified.
Radioactive isotopes, on the other hand, can't be decontaminated either easily or rapidly. In many cases the only practical thing to do with these dangerous poisons is to wait until their own slow decay can render them harmless, which takes a very, very long time.
If humanity does embark on a full scale fission power program it will, in essence, be grabbing an almost immortal tiger by the tail. Our next column will examine the question of whether or not—if we do grab the beast—there's any safe way to let go.
Details on the nuclear waste problem, radioactivity, and related subjects may be found in Ecoscience: Population, Resources, Environment by Paul R. Ehrlich, Anne H. Ehrlich, and John P. Holdren ($19.95 postpaid from W.H. Freeman and Co.), especially Chapter 8. Professor Holdren's analysis of the "aspirin tablet" fraud appears on page 450.
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