In the public controversy over storage of depleted uranium at Energy Solutions' site west of Salt Lake City, none of the participants have explained why DU becomes more radioactive over time, nor how fast, nor how hazardous that material is.

Uranium is a heavy metal, found in small quantities everywhere -- in the soil, the water, our foods and our bodies. An average human being has about 0.000002 of a pound of uranium in her/his body, two-thirds of which is in the bones, the rest distributed throughout the body. All uranium is radioactive; your body is slightly radioactive because of the uranium it contains. At a world-average concentration, an acre-foot of fresh water contains about a 0.0001 pound of uranium; seawater has about 100 times as much.

Some geologic processes concentrate the uranium in minerals; those with more than about 0.1 percent uranium are commercial uranium ores. From these ores, pure metallic uranium can be extracted. Since the 1940s we have known that one isotope of natural uranium --U235 -- can be used to run electric power plants or to make atom bombs. But this isotope is only about 0.7 percent natural uranium; most of the rest -- U238 -- has little use.

Processing plants enrich the U235, making 2 percent mixes for power plants or 90 percent mixes for weapons. The waste product from the enriching plants, called depleted uranium, normally contains about 0.2 percent U235; it is uneconomical to try to get it all. For long-term storage the uranium in DU is converted to a stable uranium oxide powder and packed in steel containers.

If we bring large amounts of DU to EnergySolutions it will probably be in that form. A pound of this DU has about as much radioactivity as 500 household smoke detectors.

Natural uranium, as found in uranium mines all over the world, is intimately mixed with its daughter compounds, formed inside it by radioactive decay. The most dangerous of these is radon gas, which can move into mineshafts and basements, contributing to lung cancer. These daughter products were removed in the processing to make fuels or weapons, so that DU is much less radioactive than the natural uranium from which it was made.

Over time, DU continues to decay, forming new daughter products, so its radioactivity roughly triples in the first year after processing (which has presumably already happened with the DU proposed for storage in Utah). Then, for the next 1,000 years, its radioactivity remains practically constant. In the period from 1,000 to 1 million years, delayed radioactive daughter products accumulate, increasing the radioactivity of the DU by a factor of about six (depending a bit on how thoroughly the DU was processed). Most of that radioactivity is due to radon and its immediate daughter products.

From now to forever, the radioactivity of the DU will be less than that of the uranium ore from which it was made, because of the removal (depletion) of U235, for fuel or weapons.

If we bury the DU at the EnergySolutions facility, as long as someone maintains the soil cover and clay water barrier, the DU can't escape. After about 1,000 years, some part of the newly produced radon gas will work its way out of the landfill to the surface.

If the soil and clay covers are intact, most of that radon will remain inside the buried waste and continue its decay, but some of it will mix with the global atmosphere (which already has a little radon gas in it).

If our descendants have forgotten what is buried there, and have forgotten how to make and use radon detectors, then they might build on top of that buried waste. The radon seeping out of the ground could enter their houses and increase their lung cancer rate. That possibility is the principal hazard of this material. It will never emit as much radon as it would have if left in the ground as uranium ore, but at EnergySolutions we will have collected much of it in one place, instead of leaving it dispersed as dilute ore, and much of it will be buried closer to the surface than it would have been if we had left it in the uranium ore deposits.

I take no stand on whether we should allow this material to be buried in Utah. But I do believe the discussion leading to that decision should be based on facts, not on misinformation and/or hysteria.

Noel de Nevers is a retired University of Utah professor of chemical engineering, with no connection to the nuclear industry or EnergySolutions.