Plutonium May Be Hitching a Ride on Colloids

If nuclear waste leaks out of its underground containers, how far is it likely to migrate? That’s a critical question to answer, with hundreds of thousands of cubic meters of waste from nuclear power and nuclear weapons operations now awaiting permanent burial. It has long been thought that at least one of the more toxic contaminants—plutonium—would stay put. Because of its low solubility in water and its tenacious capacity to cling to mineral surfaces, some argued, plutonium would remain adsorbed on local rocks. That viewpoint has been challenged in the last 15 years by suggestions that plutonium can adhere to submicrometer‐sized colloids and thereby be transported considerable distances by groundwater. This suggestion, however, has not been strongly supported by field studies. A recent study by researchers from Lawrence Livermore National Laboratory and Los Alamos National Laboratory now provides the firmest evidence to date that, at least in one case, the plutonium has migrated 1.3 km from its source in 30 years—a speed that is consistent with the flow: of groundwater in the area.