One of the risks of long-term storage of highly radioactive nuclear wastes could be reduced by a factor of 100 or more if the storage facility imitated the ocean chemically, a team of government and private researchers said last week.
Their discovery, which has been tested only in the laboratory, would be a modification of a storage method now used in France and Belgium, but only under consideration for the United States and other nuclear-powered countries. The current method involves mixing the sludgelike wastes, partly dissolved in acid, with melted glass and then pouring the mixture into stainless steel canisters. After the glass cools and hardens, the sealed canisters would be buried.
The steel is expected to resist corrosion for about 300 years. After that, however, it would be possible for ground water to reach the glass and slowly corrode it, releasing radioactive matter into the water table.
The modification "will prevent the glass from corroding for at least 25,000 years," according to Sidney Alterescu of NASA's Goddard Space Flight Center in Greenbelt.
The idea emerged from the work of John A. O'Keefe, a Goddard geophysicist who studies tektites, hardened droplets of natural glass formed when meteorites land with enough force to melt and splash rock.
O'Keefe and his colleagues have found that tektites recovered from the ocean, where some fell millions of years ago, are far less corroded than those of comparable age found on land. Experiments by Aaron Barkatt of the Catholic University of America have established that sea water's dissolved magnesium makes the difference. The magnesium-rich water forms a protective coating on the glass.
One way to use the discovery, the scientists suggest, would be to mix nontoxic magnesium compounds, such as Epsom salts, into the earth around the canisters. When the groundwater breaches the canisters, it will resemble the ocean chemically and coat the glass.