What is Finland’s nuclear waste burial plan?

Finland’s Nuclear Waste Solution. IEEE Spectrum,  By Sandra Upson 30 Nov 2009 Here on Olkiluoto Island, the forest is king. Elk and deer graze near sun-dappled rivers and shimmering streams, and humans search out blueberries and chanterelle mushrooms. Weathered red farmhouses sit along sleepy dirt roads in fields abutting the woods. Far beneath the vivid green forest, deep in the bedrock, workers are digging the labyrinthine passages and chambers that they hope to someday pack with all of Finland’s spent nuclear fuel.

Posiva, the Finnish company building an underground repository here, says it knows how to imprison nuclear waste for 100 000 years. These multimillennial thinkers are confident that copper canisters of Scandinavian design, tucked into that bedrock, will isolate the waste in an underground cavern impervious to whatever the future brings: sinking permafrost, rising water, earthquakes, copper-eating microbes, or oblivious land developers in the year 25 000. If the Finnish government agrees—a decision is expected by 2012—this site will become the world’s first deep, permanent repository for spent nuclear fuel.

Of course, not everyone shares Posiva’s confidence. ”It’s deep hubris to think you can contain it,” says Charles McCombie, executive director of the Association for Regional and International Underground Storage, based in Switzerland.

There’s more at stake here than the interment of 5500 metric tons of spent Finnish fuel. More than 50 years after the first commercial nuclear power plants went operational in the United Kingdom and the United States, the world’s 270 000 metric tons of spent nuclear fuel remain in limbo. After it gets swapped out of a reactor, utilities put it in specially designed pools, where chilled, circulating water absorbs the initial heat and radioactivity. After about five or six years, the fuel has cooled considerably, enabling utilities with limited pool space to load it into huge, million-dollar steel casks that are left to sit on concrete pads within guarded compounds.

The arrangement is far from ideal. The waste will emit harmful levels of radioactivity for thousands of years to come, and the casks are expected to last for a couple of hundred years, at most. The lack of a more permanent option is one of the biggest problems facing the global nuclear-power industry, which has been stalled for decades…….

Onkalo’s underground tunnels won’t even begin to address the global situation. But they will do the next best thing. This project, estimated to cost 3 billion ($4.5 billion), will either demonstrate that the technical, social, and political challenges of nuclear waste disposal can be met in a democratic society, or it will scare other such countries away from the repository idea for decades to come.

So far, Posiva has carved out nearly 5000 meters of tunnels and shafts, excavated more than 100 000 cubic meters of rock, and collected rock samples from 53 deep boreholes. Over the next three years, it will try to prove to the government that its canisters and deep chambers will contain radioactive waste no matter what happens to Finland. If Posiva succeeds, the repository will open for business in 2020. A hundred years later, the final canister will be buried, and the tunnels will be filled in, covered up, and artfully abandoned to a cover of pine needles and mushrooms. Finland’s first nuclear era will be over.

It’s damp and drippy in Onkalo’s passageways. From the tunnel’s entrance, a low, guttural hum reverberates in the dark. Somewhere in the blackness, a machine is drilling and blasting its way steadily downward, and construction workers are scurrying in its wake to check the ceiling for rocks that have been jostled loose in the explosions. The jumbo-size drilling machines are trundling down a 5.5-meter-wide tunnel that grows by about 5 meters a day, says junior construction manager Karoliina Lehesvuori……..

From all sides, water glistens on the rock face and collects into mud on the tunnel floor. The droplets are leaking into the tunnel from tiny fractures in the rock, smaller than a millimeter, at a rate of about 20 liters per minute. In tunnel terms, that’s slow, and that’s good news. The behavior of the water in Onkalo is Posiva’s top concern. At each new depth, geologists extract slim rock cores in search of telltale ”structures”—the fractures and crevices that determine how water moves in rock. So far, Onkalo appears to have uncharacteristically few structures, which explains why the tunnel is only damp and muddy rather than flooded with a torrent of water escaping from its high-pressure home in the rock.

Water is the one agent that could seriously threaten Posiva’s design. What the company has bet on is a nested system of what it calls engineered barriers, which are enveloped by the natural barrier of gneiss bedrock. The first engineered container for the radioactive refuse is the copper burial cask, within which sits an iron insert. Each canister will then be buried in specially dug holes in the underground tunnel network and surrounded by a special clay—the second engineered barrier—through which water can slowly diffuse, but not flow. A century from now, after Finland’s last planned reactor has long been closed and its fuel has cooled, the tunnel’s empty spaces will be filled back up with rubble and clay, the final safeguard. A concrete slab will cover the entrance and, the designers hope, deter future adventurers.

In the nightmare scenario, water would somehow manage to reach the canisters, carrying with it bacteria that burrow through the clay and erode the metal containers. The fuel rods would become exposed to the clay, and the water would carry harmful radionuclides from the fuel back to the surface………

The first challenge for Posiva was to locate a spot where no one would ever be likely to dig a deep hole. Then they had to figure out how to make and seal a container so perfectly that the weld would maintain its integrity through the next ice age, which might come as soon as 20 000 years from now.

”We needed a place that was very boring,” explains Johanna Hansen, Posiva’s research and development director. Rather than putting up elaborate signage to communicate with their far-future descendants, Hansen and her colleagues are betting that humanity will simply never want to dig here. They’d scanned the entire country for spots with no valuable metal deposits. They’d sampled groundwater all over Finland in search of the most saline, inhospitable locations. Pristine Olkiluoto passed muster. Olkiluoto’s residents, who were already sharing their island with two nuclear power plants—and were acutely aware of its lack of resources—welcomed the possibility of well-paying jobs for a century to come.

Their confidence that the project will be safe and well managed is unusual and not strongly supported by the historical record of government handling of other forms of high-level nuclear waste. In the Soviet Union, old nuclear submarines were simply abandoned along with their reactors and spent fuel in the Arctic Ocean. In the United States, at the decommissioned military reactor complex in Hanford, Wash., an estimated 1.67 trillion liters of low-level radioactive waste and more than 3 million liters of high-level waste have contaminated the soil and groundwater, and the radionuclides continue to leach into the nearby Columbia River. Unsettling lapses have also occurred at facilities in Sellafield in Cumbria, England; at the Savannah River in South Carolina; and at La Hague in northern France……..

Once the canisters are in place, the tunnels will be filled with a blend of more bentonite and excavated rock. ”We know that the bedrock is 1.8 billion years old and hasn’t changed since it was created,” says Hansen. ”We must try to maintain the bedrock as it was, so that the conditions return to how they were before we started disposal.” Now, however, the bedrock will contain the highest local concentration of uranium in the world, and the new geology must hold strong for a period of time that’s almost absurdly beyond human reckoning.

But in repository design, everything is relative. A thousand centuries may seem like a long time, but for nuclear waste it’s just the beginning. Spent nuclear fuel is mostly uranium-238, with a half-life of 4.46 billion years. The longer the half-life of the isotope, the less radioactivity it emits—but that’s not the full story. Some harmful isotopes are less likely to attach themselves to clay or rock, and therefore they are more likely to move around. ”In terms of the stuff that could make it out in hundreds of thousands of years, iodine-129 and cesium-135 would be on the list,” says John Kessler, a spent-fuel-management expert at the Electric Power Research Institute, in Charlotte, N.C. ”But over a million years, the uncertainties are pretty big.”……..

In as little as 20 000 years, Finland may enter an ice age, and advancing ice sheets kilometers thick could carve out the rock and force more water into its fractured depths. The liquid may then diffuse through the bentonite barrier, eat through the copper, and carry off still-hot radionuclides. No one can be sure.

But maybe nobody will be here to care. In 1000, 10 000, or 100 000 years, it might not be unreasonable to think our descendants will have abandoned this toxic land for a cozier alternative, on space pods or newly colonized planets. Where once there were humans, now hermaphroditic fish and finned flamingos may slither through our poisonous landscapes. Or perhaps evolution’s charge will have delivered beings who are healthier, cuter, and more intelligent than the ones designing today’s disposal systems. Or evolution may go in the opposite direction and cockroaches will reign supreme, just as we always suspected they might……http://spectrum.ieee.org/energy/nuclear/finlands-nuclear-waste-solution

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One Response to “What is Finland’s nuclear waste burial plan?”

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