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Deep-sea muds hold tight to 'hot' elements.

Deep-sea muds hold tight to 'hot' elements

No one wants nuclear waste in their backyard, so why not throw it into the sea? That may sound like environmental blasphemy, but two oceanographers report that seafloor sediments can lock away dangerous radioactive elements for hundreds of thousands of years.

Marine geologists have explored the possibility of "sub-seabed disposal" since 1974. According to the basic plan, nations could bury their high-level "rad-trash" below the ocean floor by sealing it in torpedo-shaped steel canisters, then dropping them off ships. The canisters would speed downward through 5 kilometers of water and plow tens of meters into the soft muds that blanket the deep ocean plains. Over the next 100,000 years, the sediment layer would have to prevent waste from leaking into the ocean.

To see how well the plan might work, Sarah Colley and John Thomson of the Institute for Oceanographic Sciences in Godalming, England, studied a 30-meter-long sediment core from an abyssal plain in the northeast Atlantic Ocean. These sediments naturally contain traces of uranium-238, some of which has decayed over time into uranium-234, thorium-230, radium-226 and finally lead-210.

Colley and Thomson compared the relative amounts of the radioactive isotopes to determine whether any had migrated appreciably through the sediments. They found that the uranium and thorium have not moved significantly during the last 500,000 years and the radium has moved only a short distance. Detailed in the July 19 NATURE, the study is the first to investigate migration of radioactive isotopes at depths where the waste would be buried, Thomson says. The findings contradict previous studies of shallower sediments, which suggested uranium-234 should be more mobile.

Thomson calls the new results a "positive sign" for sub-seabed disposal, but he notes that real waste could behave very differently. For instance, the canister's descent through the mud and the waste's radioactive heat might render the isotopes more mobile.

In 1986 -- the year after the deep-sea cores were drilled -- the U.S. Energy Department stopped funding studies on sub-seabed disposal. "The whole effort just vanished," says Charles D. Hollister of Woods Hole (Mass.) Oceanographic Institute, who led the U.S. work in this field. He believes the Energy Department did not want the prospects for sub-seabed disposal to slow momentum toward selecting Nevada's Yucca Mountain as a dump site. Under congressional mandate in 1987, the department began examining Yucca Mountain as the primary candidate for housing the nation's high-level radioactive waste, which comes from nuclear power plants.

Walter L. Warnick of the Energy Department says budgetary cuts led to the program's demise. Warnick heads the department's office of sub-seabed disposal research, a "ghost" office with neither funds nor staff.

In a more favorable political climate, sub-seabed disposal might gain renewed attention, Hollister says. "Eventually, the deep-sea sediments are going to be found very useful for isolating not only radioactive waste but other heavy metals as well," he predicts.
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Title Annotation:disposing of nuclear waste in the ocean bottom
Author:Monastersky, Richard
Publication:Science News
Date:Jul 21, 1990
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