[I recommending you also read my book review of Too Hot to Touch: The Problem of High-Level Nuclear Waste by William M. Alley & Rosemarie Alley. 2013. Cambridge University Press to understand how serious the problem is. Alice Friedemann www.energyskepticlcom ]
Cornwall, W. July 10, 2015. Deep Sleep. Boreholes drilled into Earth’s crust get a fresh look for nuclear waste disposal. Science Vol. 349: 132-135
One of the world’s biggest radioactive headaches sits in an aging cinderblock building in the desert near Hanford, Washington, at the bottom of a pool of water that glows with an eerie blue light. The nearly 2000 half-meter-long steel cylinders are filled with highly radioactive cesium and strontium, leftover from making plutonium for nuclear weapons. The waste has been described as the most lethal single source of radiation in the United States, after the core of an active nuclear reactor. It could cause a catastrophe if the pool were breached by an unexpectedly severe earthquake, according to the U.S. Department of Energy (DOE), the waste’s owner.
For decades, the federal government has been floundering over what to do with the cylinders. They’re too hot to be easily housed with other waste. And the government’s quest to create a single permanent burial ground for all the nation’s high-level nuclear waste, from both military and civilian activities, is in disarray. U.S. high-level nuclear waste:
70,000 metric tons of civilian waste stored at 75 sites
13,000 metric tons of military waste stored at 5 sites
Now, a deceptively simple-sounding solution is emerging: Stick the cylinders in a very deep hole. The approach, known as deep borehole disposal, involves punching a 43-centimeter-wide hole 5 kilometers into hard rock in Earth’s crust. Engineers would then fill the deepest 2 kilometers with waste canisters, plug up the rest with concrete and clay, and leave the waste to quietly decay.
The idea has been around for decades, but not long ago scientists had all but abandoned it. Over the past 5 years, however, as improved drilling technologies converged with the political and technical woes bedeviling other nuclear waste solutions, boreholes have regained their allure. DOE has gone from spending almost nothing on borehole research to planning a full-scale field test, costing at least $80 million. And earlier this year U.S. Energy Secretary Ernest Moniz gave boreholes a dash of publicity during a major speech, mentioning them as a promising way to deal with the cesium and strontium waste at DOE’s Hanford Site nuclear complex.
Boreholes have “been plan B and just missed the boat for years,” says nuclear engineer Michael Driscoll, a retired professor from the Massachusetts Institute of Technology (MIT) in Cambridge and one of the concept’s leading advocates. “Maybe now is the time.
Many nuclear waste veterans, however, are skeptical. The technical challenges are daunting, they argue, and boreholes won’t end political opposition to building new nuclear waste facilities. “The borehole thing to me is a red herring,” says attorney Geoff Fettus of the Natural Resources Defense Council (NRDC) in Washington, D.C., which supports underground disposal in a shallower mine, but has sued DOE over now abandoned plans to bury the waste inside Nevada’s Yucca Mountain.
Still, even some doubters say that given the current deadlock over nuclear waste, boreholes deserve a second look, at least for those troublesome cylinders at Hanford.
“If we can move forward with disposing of some of the DOE waste, that’s a good thing,” says geoscientist Allison Macfarlane, director of the Center for International Science and Technology Policy at George Washington University in Washington, D.C., and a former chair of the U.S. Nuclear Regulatory Commission. “We have to make some progress somewhere.
IF ONE PERSON deserves credit for helping revive U.S. borehole research, it’s Driscoll, the retired MIT engineer. Now 80, he has spent more than 25 years quietly exploring the potential for depositing radioactive waste deep in granite bedrock.
Driscoll wasn’t the first to pursue the idea; since the 1950s, boreholes have vied with other nuclear waste disposal options, ranging from the improbable (shoot it into outer space or melt it into an ice sheet) to the mundane (stash it in a shallow mine). Ironically, by the time Driscoll got interested in boreholes, U.S. policymakers thought they had settled the issue. In 1987, after years of fierce debate, Congress approved legislation creating a national repository for high-level nuclear waste in a mine carved into Yucca Mountain, roughly 110 kilometers northwest of Las Vegas, Nevada. With that decision, U.S. funding for borehole research largely evaporated.
Driscoll wasn’t deterred. Boreholes, he thought, had some potential advantages over a single big facility. For example, they could spread the burden of storing waste that no one wanted, because suitable rock is found across the United States. So even as engineers began to plan the Yucca Mountain repository, Driscoll and a handful of graduate students kept churning out papers delving into borehole costs and technical feasibility.
In one scenario they explored, spent fuel rods are placed in slender canisters that are strung together like sausage links, then lowered into the hole. Even very radioactive material would be safe, advocates say, if placed in the right kind of deep rock: ancient crystalline granite with few cracks that might allow radioactive materials to seep into groundwater or reach the surface. The surrounding rock and the salty water would dissipate heat generated by the waste. And the top 3 kilometers of each hole would be plugged with a layer cake of cement, gravel, and bentonite clay, which swells when wet. The nation’s entire cache of high-level waste could fit into 700 to 950 boreholes, at a cost of $40 million per hole (not counting transportation), according to recent estimates by scientists at DOE’s Sandia National Laboratories in Albuquerque, New Mexico, who have worked with Driscoll.
Boreholes got their first big break in 2010, when the Obama administration announced that it was abandoning Yucca Mountain after years of delays and resistance from state politicians. The government began looking for other options. That year, Sandia made its first big investment: $734,000 to study how fluid and radioactive particles might behave in a borehole, and how best to seal it. In 2012, a presidential commission added its recommendation for more studies.
Soon after, Moniz became energy secretary. Moniz, a former colleague of Driscoll’s at MIT, had already heard his sales pitch about boreholes. In 2003, the two men served together on a study panel that endorsed “aggressively” studying the technology.
This past March, a White House policy shift opened the door further. Moniz announced that the Obama administration would abandon previous plans to put all high-level waste in one spot and instead would seek separate sites for disposing of commercial nuclear waste—about 85% of the total—and military waste. Moniz called some of the defense waste, including Hanford’s radioactive cylinders, “ideal candidates for deep borehole disposal.
CESIUM-137 AND STRONTIUM-90 are the hot potatoes of the nuclear waste world, packing a powerful radioactive punch in a relatively short half-life of 30 years. At Hanford, there’s barely enough to fill the back of a pickup truck. Yet it contains more than 100 million curies of radiation, roughly one-tenth the radiation in the core of a large nuclear reactor. And it produces enough heat to power more than 200 homes.
To prevent the tubes from causing trouble, they sit under about 4 meters of water in what resembles a giant swimming pool, emanating a blue glow known as Cherenkov radiation as high-energy particles slam into the water. The 1974 building housing the pool is past its 30-year life span, according to DOE’s inspector general. Bombarded by radiation, the pool’s concrete walls are significantly weakened in places. Some of the tubes have failed and been stuck inside larger containers. In a review of DOE facilities conducted after the 2011 disaster at Japan’s Fukushima Daiichi Nuclear Power Station, the department’s Office of Environmental Management concluded that the Hanford pool had the highest risk of catastrophic failure of any DOE facility, for example in a massive earthquake, according to a report from the department’s inspector general. DOE says it plans to move the pool waste into dry casks for safer storage, but it hasn’t said when.
“It’s an urgent situation and a huge safety risk,” says Tom Carpenter, executive director of the watchdog group Hanford Challenge in Seattle, Washington, which has been critical of DOE’s efforts to secure the waste.
Borehole advocates point out that the Hanford tubes are less than 7 centimeters in diameter, narrow enough to fit down a hole without extensive repackaging. All could fit into a single shaft. Other military waste could also go down a borehole, advocates add. One candidate is plutonium that DOE has extracted from dismantled nuclear weapons. Most of it is currently stored as softball-sized metal spheres at a DOE facility in Texas. In contrast to Hanford’s cesium and strontium, the plutonium is fairly cool, but extremely long-lived, with a half-life of 24,000 years. DOE is considering other options for the plutonium, including turning it into fuel for nuclear reactors or combining it with other nuclear waste and burying it. But boreholes could be an effective way to put it far out of the reach of anyone trying to lay their hands on bombmaking material.
Yet borehole disposal is not as straightforward as it might seem. The Nuclear Waste Technical Review Board, an independent panel that advises DOE, notes a litany of potential problems: No one has drilled holes this big 5 kilometers into solid rock. If a hole isn’t smooth and straight, a liner could be hard to install, and waste containers could get stuck. It’s tricky to see flaws like fractures in rock 5 kilometers down. Once waste is buried, it would be hard to get it back (an option federal regulations now require). And methods for plugging the holes haven’t been sufficiently tested. “These are all pretty daunting technical challenges,” says the board’s chair, geologist Rod Ewing, of Stanford University in Palo Alto, California.
Even if those technical problems are surmounted, boreholes might solve only a fraction of the nation’s waste problem. That’s because much of the high-level waste simply wouldn’t fit down a hole without extensive repackaging. “Due to the physical dimensions of much of the used nuclear fuel, it is not presently considered to be as good of a candidate [for borehole disposal] as the smaller waste forms,” said William Boyle, director of DOE’s Office of Used Nuclear Fuel Disposition Research and Development, in a statement to Science. Spent fuel rods from commercial power reactors, for instance, are often bundled into casks that are about 2 meters across.
Then there’s the same problem that dogged Yucca Mountain: the politics of finding a place to drill the holes. “Let’s just assume [boreholes] could work better than anybody ever imagined,” says Fettus, the NRDC attorney. “You still wouldn’t solve the nut that everyone has been unable to solve”: persuading state and local governments to take on waste from across the nation.
DESPITE THESE CHALLENGES, Sandia scientists are moving forward with a 5-year plan to drill one or more 5-kilometer-deep boreholes. Pat Brady, a Sandia geochemist helping plan the tests, is optimistic. “There’s a lot of institutional experience with drilling holes in the ground,” he says.
The drilling technology is better than ever, he says. Drillers have gained valuable experience boring deep holes into hard rock for geothermal energy, and improved rigs can more easily and accurately drill deep, straight holes. The Sandia team is currently looking for a U.S. site for the first test hole, with a plan to start drilling in the fall of 2016.
Besides seeing if they can cost-effectively drill a hole that’s deep and wide enough, they also want to test methods for determining whether the rock is solid and whether any water near the bottom of the hole is connected to shallow groundwater. Then they will lower a model waste canister down the hole to see if it gets stuck.
Other nations with nuclear waste, including China, are watching. But, for now, the United States is the only country getting ready to drill. “Nobody else has stepped forward,” says Geoff Freeze, a nuclear engineer at Sandia who is overseeing the U.S. experiment. “It kind of fell to us.”