Proposals to bury plutonium from nuclear weapons must address chemical interactions and intrusion risks, say Cameron L. Tracy, Megan K. Dustin and Rodney C. Ewing. More than 600 metres below ground near Carlsbad, New Mexico, is the world’s only operating deep geological repository currently accepting transuranic nuclear waste: that contaminated by elements heavier than uranium. The Waste Isolation Pilot Plant (WIPP), run by the US Department of Energy (DOE), is used to dispose of laboratory equipment, clothing and residues from the nation’s nuclear-defence programme. In the past 15 years, around 91,000 cubic metres (equivalent to covering a soccer field to a depth of about 13 metres) of such transuranic waste, mostly of relatively low radiation levels, has been placed there. An arms-control agreement with Russia made in 2000 obliges the United States to dispose of 34 tonnes of plutonium from dismantled nuclear weapons. Following the terms of the agreement, the United States planned to convert the material into a fuel — mixed (uranium and plutonium) oxide, or MOX — to burn in commercial nuclear-power plants. But faced with soaring construction costs for a MOX fabrication facility at the Savannah River Site in South Carolina, the DOE has commissioned evaluations of alternatives. The most recent report, published in August 2015, recommends burying the weapons’ plutonium at WIPP. Judging the repository’s performance to have been “successfully demonstrated”, the DOE’s Red Team expert panel proposes that the 34 tonnes of weapons plutonium can be added to WIPP once it has been diluted to low concentrations comparable to that of the transuranic waste at WIPP. Before expanding WIPP’s plutonium inventory, the DOE must examine more carefully its safety assesment for performance that stretches to 10,000 years and beyond.
Nature 13th Jan 2016 read more »