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March 24, 2011

Plutonium in perspective

Bernard L. Cohen, describes the situation with Plutonium

One often hears that in large-scale use of plutonium we will be creating unprecedented quantities of poisonous material. Since plutonium is dangerous principally if inhaled, it should be compared with other materials which are dangerous to inhale. If all of our electricity were derived from breeder reactors, we would produce enough plutonium each year to kill a half trillion people.* But as has been noted previously in Chapter 5, every year we now produce enough chlorine gas to kill 400 trillion people, enough phosgene to kill 18 trillion, and enough ammonia and hydrogen cyanide to kill 6 trillion with each. It should be noted that these materials are gases that disperse naturally into the air if released, whereas plutonium is a solid that is quite difficult to disperse even intentionally. Of course, plutonium released into the environment will last far longer than these gases, but recall that the majority of the harm done by plutonium dispersal into the environment is due to inhalation within the first hour or so after it is released. The long-lasting nature of plutonium, therefore, is not an important factor in the comparisons under discussion.



I have been closely associated professionally with questions of plutonium toxicity for several years, and the one thing that mystifies me is why the antinuclear movement has devoted so much energy to trying to convince the public that it is an important public health hazard. Those with scientific background among them must realize that it is a phony issue. There is nothing in the scientific literature to support their claims. There is nothing scientifically special about plutonium that would make it more toxic than many other radioactive elements. Its long half life makes it less dangerous rather than more dangerous, as is often implied; each radioactive atom can shoot off only one salvo of radiation, so, for example, if half of them do so within 25 years, as for a material with a 25-year half life, there is a thousand times more radiation per minute than emissions spread over 25,000 years, as in the case of plutonium.

A pound of Plutonium on a city would be about 11-27 deaths

In evaluating the hazards from plutonium toxicity, it gives little insight to say that we can expect 2 million cancers per pound of plutonium inhaled unless we specify how much plutonium would be inhaled in various scenarios. This, of course, depends on the type of release, the wind and other weather conditions, as well as the number of people in the vicinity. But let us say that one pound of plutonium oxide powder gets released in the most effective way in an average big city location under average weather conditions. In the hour or so before the wind blows dust out of the densely populated areas, only about 1 part in 100,000 would be inhaled by people, enough eventually to cause 19 cancers. If people know about the plutonium, as in a blackmail situation, they could breathe through a folded handkerchief or piece of clothing, which would reduce the eventual death toll from 19 to 3. Better yet, they could go inside buildings and shut off outside air intakes for this critical short time period.

Eventually all of the plutonium dust would settle down to the ground, but there would still be the possibility of its later being resuspended in air by wind or human activities. Its ability to be resuspended is reduced by rain, dew, and other natural processes, as a result of which the principal threat from this process diminishes rapidly over the first year and essentially disappears thereafter. All in all, this resuspended plutonium dust eventually causes about seven deaths.

Within a few years the plutonium works its way downward into the ground, becoming a permanent part of the top layers of soil. As is well known, it remains radioactive for a very long time. How much harm it does over that period depends on its probability of getting suspended in air by plowing, construction, or natural processes, and then being inhaled by humans. Due to these processes, an average atom of a heavy metal in the top eight inches of soil has 13 chances in a billion of being inhaled by a human each year. If this probability is applied to the plutonium, it will cause a total of only 0.2 additional deaths over the tens of thousands of years that it remains radioactive.

During this period, plutonium in the soil can also be picked up by plant roots, thereby getting into food. This process has been studied in many controlled experiments and in various contamination situations such as bomb test sites and waste disposal areas. Its probability is highly variable with geography, but even under the most unfavorable conditions, this would lead to less than one additional fatality over the tens of thousands of years.

In summary, a pound of plutonium dispersed in a large city in the most effective way would cause an average of 19 deaths due to inhaling from the dust cloud during the first hour or so, with 7 additional deaths due to resuspension during the first year, and perhaps 1 more death over the remaining tens of thousands of years it remains in the top layers of soil. This gives and ultimate total of 27 eventual fatalities per pound of plutonium dispersed.

It has often been suggested that plutonium dispersion might be used as an instrument for terrorism. But this is hardly realistic because none of the fatalities would occur for at least 10 years,* and most would be delayed 20 to 40 years. It could not be used for blackmail because if the dispersal is recognized, protective action is easily taken — breathing through handkerchiefs, or going indoors. Terrorists would do much better with nerve gas, which can be made from readily available chemicals; it leaves dead bodies at the scene.

There have been fears expressed that we might contaminate the world with plutonium. However, a simple calculation show that even if all the world's electric power were generated by plutonium-fueled reactors, and all of the plutonium ended up in the top layers of soil, it would not nearly double the radioactivity already there from natural sources, adding only a tiny fraction of 1% to the health hazard from that radioactivity. As is evident from the previous discussion, plutonium in the ground is not very dangerous, because there is no efficient mechanism for transforming it into airborne dust.

Current Environmental Protection Agency (EPA) regulations require that no more than about one part in a billion of the plutonium handled by a plant escape as airborne dust.43 All plants now operate in compliance with that regulation. It is 100,000 times less than the releases Gofman has been assuming. If all of the electricity now used in the United States were derived from breeder reactors, the maximum allowable releases would be 0.0007 pounds per year. If all plants were in large cities, where we have shown that plutonium releases cause 27 deaths per pound, this would correspond to one fatality every 50 years somewhere in the United States. Since these facilities would not be in cities, the consequences would be considerably lower, much less than one death per century.

Of course, the EPA regulations do not cover releases in accidents, and there have been some of these. Two of the most notable were fires in a Rocky Flats, Colorado, plant for fabrication of parts for bombs, where plutonium is handled in a flammable form (the forms used in the nuclear power industry are not flammable).44 In the earlier fire in 1957, about 1 part in 300,000 — .002 ounces — of the plutonium that burned escaped as dust.* After that, many improvements were made, so that in the much larger fire in 1969, only 1 part in 30 million of the plutonium that burned escaped. Safety analyses indicate that new improvements will considerably reduce even this low figure.

The most important effects of plutonium toxicity by far are those due to nuclear bombs exploded in the atmosphere. Only about 20% of the plutonium in a bomb is consumed, while the rest is vaporized and floats around in the Earth's atmosphere as a fine dust. Over 10,000 pounds of plutonium has been released in that fashion by bomb tests to date, enough to cause about 4,000 deaths worldwide. Note that the quantity already dispersed by bomb tests is more than 10 million times larger than the annual releases allowed by EPA regulations from an all breeder reactor electric power industry.

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