With Yucca Mountain now an afterthought for disposing the nation’s highly radioactive waste, one federal geologist says he might have other places to put it than the volcanic-rock ridge 100 miles northwest of Las Vegas.
One of the many shale formations in the midcontinental United States where water is slow to escape and slow to re-enter could provide geologic containment of the 77,000 tons of used nuclear fuel and highly radioactive defense waste.
Moving the waste from reactor sites and surface storage facilities to a maze of tunnels planned for Yucca Mountain was put on hold indefinitely when the Obama administration halted the Yucca Mountain Project in 2009.
“Shale probably makes for much larger areas to consider. I’m not saying politically, but geologically shale is probably one of the most abundant rock sources there is. It’s all over,” said Chris Neuzil, a hydrogeologist with the U.S. Geological Survey in Reston, Va.
Neuzil will present his research on the topic today to colleagues attending this week’s Geological Society of America conference in Denver.
His associate, Alden Provost, provided modeling for their analysis.
The Department of Energy invested heavily in scientific studies of Yucca Mountain, spending $13 billion over a quarter of a century, only to realize that surface water moving downward through the porous ridge would require expensive titanium drip shields to prevent metal waste containers from corroding.
Meanwhile, little attention was paid to studying shales and other clay-rich rocks, unlike the efforts of scientists from European countries saddled with a nuclear waste disposal burden.
“Shale has essentially been off the radar for the whole repository program. That’s the contrast with countries like France, Belgium and Switzerland,” Neuzil said Thursday. “Once that Yucca Mountain was killed, I said, ‘Let’s look at this. Maybe we need to consider shale.’ ”
What makes shale a good medium for containing nuclear waste is its low permeability, he said.
The key to selecting a shale site is to find one thick enough and deep enough to drill a large shaft for lowering equipment and crews to mine a horizontal tunnel that follows the middle of the formation. The consensus among European scientists who have been studying shale sites is to find ones that are 1,500 feet to 3,000 feet deep, enough for safe isolation of the waste but “not so deep that it becomes a technical nightmare,” Neuzil said.
He explained that shale acts like a sponge in slow motion. Once water has been squeezed out, it takes a relatively long geologic time for the shale to soak it back up.
Entombing waste containers in shale for the time it takes their radioactive contents to decay to safe levels hopefully wouldn’t require drip shields to protect the containers.
“My understanding suggests if it did, that would be a major disappointment,” he said.
U.S. researchers are intrigued by what Canadian scientists learn from shale permeability observations at a proposed, 1,200-foot-deep nuclear waste repository, the Bruce Nuclear Site in Ontario.
“This is usually difficult to demonstrate, but some shales have natural groundwater pressure anomalies that can be analyzed — as if they were permeability tests — on a very large scale,” Neuzil said in a news release about the Geological Society of America conference.
Contact reporter Keith Rogers at firstname.lastname@example.org or 702-383-0308.