An article published today in the scientific journal Nature warns the United States Government about the possible long-term risks of burying 34 tons of plutonium from nuclear weapons in a deposit more than 600 meters deep in Carlsbad, New Mexico.
The US Department of Energy, which is obliged to take charge of these wastes under an agreement signed with Russia in 2000, is evaluating confining this waste material in its Waste Isolation Pilot Plant (WIPP), the only Geological Warehouse. Deep (AGP) that exists in the world.
Hundreds of thousands of plastic-lined steel drums already line the bottom of that facility, carved out of rock to the level of a 250-million-year-old saline bed.
The deposit has reached half its capacity and will be permanently sealed in 2033, so that the residues of plutonium-239 and other radioactive materials, with a half-life of more than 24,000 years, will be encapsulated for millennia.
The original plan of the United States was to convert this military waste into fuel for fission reactors, but the high cost of the plant projected for that purpose in South Carolina has led the Department of Energy to consider an alternative plan.
The scientists signing the Nature paper, led by Stanford University Nuclear Safety Professor Rodney Ewing, warn that long-term risks of storing plutonium in WIPP, such as unexpected chemical reactions, have not been taken into account. in waste materials.
The brief stresses that the United States has a responsibility to ensure that the facility is safe for at least 10,000 years, an extreme that was questioned after an incident in February 2014.
One of the nuclear waste by-products reacted unexpectedly with the material in the drum containing it, causing a radioactive gas leak through the ventilation channels that expanded about 900 meters and exposed 21 workers to levels. low radioactivity.
Scientists consider that this accident, although not very serious, illustrates the difficulty of predicting potential failures of a facility that must operate for millennia.
“The Department of Energy has perfectly identified the causes (of that incident) and has implemented corrective measures. Incompatible chemicals are no longer mixed in the drums, ”the experts agree.
"However, once the repository is closed, it will not be possible to monitor its content or correct problems," they warn.
The reservoir's design is confident that the saline bed on which it sits would prevent radioactive material from leaking out in the event the barrels broke, a scenario that scientists say has not been studied enough.
In addition to the danger of an accident occurring inside the facility once sealed, scientists warn that in thousands of years someone could drill in that area for gas or oil, causing a radioactive leak.
“We cannot be sure that future inhabitants of that area will know that the WIPP is there. To put the time scale we are talking about in perspective, agriculture developed only 10,000 years ago, ”the letter states.
Saline sediments often indicate the presence of mineral and energy resources, so the possibility of someone trying to drill at that location in the next few millennia is "significant."
Given those risks, scientists believe that to store military plutonium in WIPP its ability to stay safe for at least 24,000 years must be reassessed.