Tech + Engineering

27
Aug

A Salty Solution for Nuclear Waste

Our caravan of SUVs pulls into a parking lot in the middle of four square miles of scruffy, unassuming brown desert 26 miles outside Carlsbad, New Mexico. Through the front window, I can see a row of semi-trailers loaded with drab, hulking metal and concrete casks. As I step out, the sun beats down on me with unrelenting intensity, despite the air’s slight spring chill. Above, jets streak across the cloudless, blue sky. Below, the ground conceals a national legacy, though it’s not the kind we tend to brag about. Entombed in a labyrinth of tunnels that wend their way through a 250-million-year-old salt deposit are decades of radioactive waste.

This is the only working underground nuclear waste repository in the United States. It’s failing structurally—flowing under pressure, as every salt mine does—and I’m about to go inside.

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The Waste Isolation Pilot Plant holds decades of nuclear waste.

Hardhats, headlamps, and emergency respirators secured, my tour group of college students and professors is ready for the journey below. Just before we depart, we’re given collection bags so we can snag some Permian-age salt souvenirs. We’re told that the luckiest among us will collect pieces containing ancient water droplets trapped inside air bubbles in the salt. But first we’ll need to cram into the cage-like elevator that will lower us 2,150 feet down into the mine where salt walls are slowly sealing the nuclear waste entombed within.

One Working Solution

The Waste Isolation Pilot Plant, known locally as WIPP (pronounced “whip”), opened in 1999 after decades of back and forth between state and federal regulators. Today, it holds more than 85,000 cubic meters of radioactive waste arriving from as far away as South Carolina. Currently, WIPP is only authorized to handle waste containing elements with atomic numbers higher than 92—primarily plutonium—that originated from the development and manufacture of nuclear weapons. Between 1944 and 1988, the U.S. produced about 100 metric tons of plutonium, most of which was used to develop nuclear weapons.

“We are disposing of long-lived materials here, not short-lived materials,” says Ned Elkins, WIPP program manager for Los Alamos National Laboratory, referring to the half-lives of the radioactive elements in the materials. Waste received from plutonium production facilities might include contaminated equipment, pipes or shielding, and other materials used in cleaning up or decommissioning weapons facilities.

WIPP’s operators stack waste containers in rooms dug into the salt formation and then let geology do the rest. Under pressure from the ground above, salt formations flow into cracks and open spaces. Over several dozen years, salt will settle around the containers, forming a rocky seal. That self-sealing ability also protects the site from cracks caused by earthquakes—any that open will quickly close. So far, the site has been successful in containing radiation from the waste. A monitoring center in nearby Carlsbad sensed radioactive iodine in the atmosphere in 2011, but it wasn’t from WIPP—it was from the Fukushima disaster halfway around the globe.

While WIPP has been accepting nuclear waste from weapons programs, no central repository currently exists in the U.S. for spent nuclear fuel and related waste from commercial reactors. Until one opens, waste has been sitting in interim storage at or near each of the nation’s 65 nuclear power plants. At the end of 2011, these sites and others held more than 67,000 metric tons of spent nuclear fuel, according to a report issued by the Congressional Research Service.

For decades, politicians, regulators, and scientists have been pitching, probing, and testing a ridge in the Nevada desert known as Yucca Mountain, hoping that it might be a suitable burying ground for our stockpiles of waste. But in 2009, the Obama administration moved to shelve the project by defunding it, citing concerns about the site’s safety. As the controversy over Yucca Mountain simmers, eyes are turning to the working repository I’m about to enter here in the New Mexican desert. WIPP might be the nuclear waste solution we’ve been looking for. And here’s the kicker, the residents of New Mexico are generally happy about it.

Unlike Yucca Mountain, which was selected for the area’s stable geology, the mine’s eventual structural failure is welcomed. “We did not design WIPP to stay open,” Elkins says. “Our design is centered around accentuating and speeding the process of closure, encapsulation, and re-annealing,” he adds.

Proponents of a centralized repository for nuclear waste argue that storing waste in multiple sites across the country has myriad problems, from the potential for proliferation to widespread environmental contamination. A central location may also require less security than numerous sites dispersed across the U.S., making it cheaper to operate than many distributed sites. Though Yucca Mountain may be a dead end, there’s room for expansion at WIPP, Elkins says. Other opportunities could open up, too—New Mexico is home to other suitable salt formations.

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Waste arrives at WIPP from all over the country on board trailers, which are visible near the facility's entrance.

The Department of Energy’s (DOE) Office of Nuclear Energy is again expected to take up the task of evaluating a variety of underground options for waste isolation and management, according to a report released in January. These will likely include salt, clay, and granite. With WIPP’s success, salt could be a frontrunner, says Abraham Van Luik, senior scientist and director of international programs for the DOE Carlsbad Field Office.

In April, four U.S. senators released a discussion draft of a bill that would create a new government organization—the Nuclear Waste Administration—to deal specifically with the disposal of nuclear waste, a responsibility that currently falls within the Department of Energy. The draft received more than 2,500 public comments, and in late June, an updated version was sent to the Senate Committee on Energy and Natural Resources as the Nuclear Waste Administration Act of 2013.

In July, the committee heard testimony from Energy Secretary Ernest Moniz and a number of others, including representatives for state legislators, utilities, and environmental and science advocacy groups. Most agreed that advancing nuclear waste policy was a good thing, but hammering out the details will take some time.

Based on the recommendations of the Blue Ribbon Commission on America’s Nuclear Future released early last year, the Nuclear Waste Administration would need to obtain consent from surrounding communities when selecting disposal sites, a move intended to cultivate goodwill.

While Yucca Mountain has been riddled with controversy, the people of Carlsbad asked for our nation’s nuclear waste back in the 1960s. Since then, the local economy has benefitted from the planning, construction, and maintenance of WIPP, according to a statement released by Representative Steve Pearce earlier this year. In May, Pearce introduced a bill to broaden the scope of WIPP to include government owned, non-defense waste. The list does not include uranium, though, the most common nuclear fuel used in the U.S. The bill is currently under consideration by energy and armed services subcommittees.

Even with New Mexico vying to take on more waste, an operating repository for commercial waste could be as far away as 2048, according to the proposed plan. Meanwhile, nuclear waste from power plants keeps piling up. The amount of spent fuel in temporary storage is expected to grow by roughly 2,200 tons each year, more than doubling the current amount.

Van Luik, who has built a career out of studying radioactive waste systems, spent 22 years working on Yucca Mountain before the program was halted. He now serves as a liaison for international collaboration on nuclear waste management, and he says the U.S. is falling behind. But he’s still optimistic.

Walking into WIPP

After a six-minute ride in a dark mine shaft elevator, I walk into a hazy, gray underground laboratory—WIPP is a test facility, after all. From the front seat of an electric cart, I can see that the walls carved in the salt are much smoother than I expected. As we move through a series of air-lock chambers deeper into the mine, our guide’s voice booms through the corridor. Looking up at the bulging ceiling, I’m suddenly reminded that 2,150 feet is a long way down.

WIPP Panel 7
A recently constructed corridor in Panel 7

According to the current plan, WIPP will eventually consist of eight large, excavated areas, known as panels, which are further divided into seven disposal rooms. The first five panels are already full, the sixth is currently being filled, and construction on the seventh was recently completed. The eighth panel will come later. We’re heading to Panel 6, where the action is.

Behind the immediately recognizable yellow and red radiological hazard signs, I can just make out ordinary-looking canisters and boxes in the disposal room’s darkness. They contain relatively safe waste, the kind you can snap a group photo with. The truly dangerous stuff that needs more shielding is kept in holes bored into the room’s walls and is handled remotely.

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Remotely-operated equipment loads highly-radioactive waste into holes bored in the walls.

From a distance, the walls appear smooth, but up close they are rough and brittle. When I pry at them, salt chips away easily. Golf ball sized chunks of the stuff—gray, white, pink, and yellow—litter the halls along the margins. From this perspective, it’s easy to envision how the walls are slowly closing in on us. Nothing illustrates that better than the story of Panel 1. In the 10 years that passed between when the first disposal area was excavated and when waste first entered, Panel 1 closed to the point where it could only be partially filled. Having learned from that experience, operators now begin excavations only when waste is ready and available to fill a room. It’s what Elkins calls “just-in-time” mining.

WIPP feels like it’s in constant motion—the continuous care needed to control the salt, the movement of the electric carts within the mine’s pathways, the loading of waste first into the walls and then the room, back to front. It all serves as a reminder that the place really is moving, just at a slower, inexorable pace. WIPP depends “on salt and the behavior of salt,” Elkins says. Salt flows under pressure, and it’s under a great deal of pressure this far underground. On a geologic time scale, it presses down with surprising speed, crushing and then encapsulating whatever is placed inside.

The motion that makes WIPP so valuable can also make it a daunting place to work. All that’s separating miners from collapsed tunnels are wire nets, bolts, and a series of closely monitored sensors attached to the walls and ceiling. A catastrophic collapse has never happened, but every salt surface in the mine is closing in by 2-3 inches per year. Just to keep the tunnels passable, floors are re-cut every eighteen months to maintain enough headroom.

The entire operation is balanced on a knife’s edge. “This repository can only operate as fast as we receive waste. Generally what limits, or what defines how long it takes [to fill a room], is not what we can do here but how fast sites are sending waste here,” Elkins says. “If we’re receiving waste at a rate that is consistent with what we can do, one of these rooms is about a month to a month and a half of work to fill.” But under normal working conditions, an entire panel might take as long as two years to fill.

Pressure to Solve the Problem

With Yucca Mountain now shelved, could salt be the answer for the United States? Van Luik, who has watched the rest of the world move ahead on waste burial, says yes. The first deep geological repositories for high-level waste and spent nuclear fuel are expected to begin operation in Europe between 2020 and 2025. In Finland, a site is being mined in granite. Later sites will be dug in clay in France and granite in Sweden. Germany has three salt repositories for nuclear waste, although two are now closed and a third was recently under investigation for safety reasons.

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Nuclear waste is placed in disposal rooms that are carved into the salt. In front, signs warn of the presence of radioactive material.

“Back in the 1980s, one of the three sites that was supposed to be characterized for a repository was in the Texas panhandle in a bedded salt formation,” Van Luik says. “Germany just completed 10 years of testing in a salt dome…and we’re very grateful to them for sharing their results. We learn from them,” he adds. “We make sure that we don’t repeat mistakes.”

Beyond the salt formations in Texas and at WIPP in New Mexico, there are also large salt domes and bedded deposits in Louisiana, Michigan, and Mississippi. But as we learned from Yucca Mountain, location and attitude are everything, and picking a final resting place for our nuclear waste is wrought with fear and loathing.

“It looks like some people in Congress—on both sides of the aisle—are really anxious to get this country moving forward again,” Van Luik says. “I think that this country will start to awaken to the fact that other countries are moving forward where we have been stymied by our own fears.”

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