The contaminated Molten Salt Reactor Experiment at the Oak Ridge National Laboratory in Tennessee could be encased in concrete, according to the top nuclear cleanup official at the Department of Energy site.
Oak Ridge Office of Environmental Management (OREM) Manager Jay Mullis told an environmental advisory board in November that DOE is considering the plan.
“It’s simply an evaluation at this point,” Mullis said of the entombment idea, which came up during OREM’s 45-day review, an assessment DOE uses to identify areas of improvement in environmental management.
Inspired by a 1950s molten fluoride salt reactor design for aircraft, Oak Ridge engineers built the experimental reactor as the United States began weighing its options for atomic energy production. The Molten Salt Reactor Experiment went critical in 1965 and operated for the next four years, first using plutonium and weapon-grade uranium for fuel, and then depleted uranium-233
“There are trace amounts of those fuels left,” Mullis told the board. The reactor’s salt and flush tanks are also contaminated with fission products such as cesium and strontium.
Should the plan pass muster, those tanks would be entombed in concrete to contain the contamination until it decays.
OREM’s primary cleanup challenge with the reactor is that the fuel is disseminated between the salt grains. The Energy Department removed some the fuel about 10 years ago by heating it up and sparging it. Mullis said attempts to remove the remnants risk dispersing the material.
The drain tanks run up to 1,000 Roentgens, about 200 times the calendar year exposure limit recommended for radiation workers.
“It’s a very hazardous operation for us,” Mullis said. “Because I’m not going to heat it up and drain the salt out at this point.”
Right now, the tanks are underground and covered by shield plugs, and OEEM spends money maintaining and securing the site near the lab’s High Flux Isotope Reactor.
OREM spokesman Ben Williams said the office spends about $26 million each year maintaining contaminated facilities within the Oak Ridge Reservation, including the Molten Salt Reactor Experiment at the Oak Ridge National Laboratory.
Cleaning up the reactor’s tanks could cost as much as $200 million.
“If there’s some way to get us to a safer posture much quicker, I’m certainly wanting to look at that,” Mullis told the board. The Energy Department might make a decision on the entombment by the end of the year.
The office does not yet have renderings of what it might look like, but Mullis compared it to cocoons used to contain old plutonium reactors at the Hanford Site in Washington state.
