Europe elaborates plan for labyrinths of nuclear waste

Beneath a plateau surrounded by fields of colza and wheat, the underground laboratory, located near the village of Bure, in the eastern French region of Lorraine, is run by the Agence Nationale pour la Gestion des Dechets Radioactifs, or Andra, the national authority charged with the safe disposal of nuclear waste.

The laboratory’s work is to test what might happen if spent nuclear fuel were to be stored permanently in caverns cut deep into rock. France plans to do just that; others are seeking to follow suit.

As the global nuclear power industry strives to limit the immediate fallout — both physical and political — from the accident at the Fukushima Daiichi power station in Japan, Europe is poised to enshrine a final solution for its long-term radioactive wastes, the industry’s most persistent public-relations problem.

A directive being debated in Brussels would commit the continent to following the example of France, Finland and Sweden, which are preparing to dig deep underground labyrinths to store the highly toxic waste forever.

The directive, which is expected to come before the European Parliament on June 22, would oblige all 27 members of the European Union to submit plans to the European Commission, the bloc’s executive arm, for similar nuclear waste repositories deep underground.

Spent fuel is stockpiled at present in interim storage facilities with a life span of 50 years to 100 years, yet some of the elements that it contains remain radioactive for up to a million years.

Scientists have been researching the idea of burying such waste deep in the Earth’s crust for much of the past half century; Finland, Sweden and France decided to go ahead with deep disposal projects about a decade ago.

The task is unlike any other because of the sheer amount of time involved. Setting up geological repositories takes decades, starting with studies to find a suitable rock structure, and testing the metals that could be used to build waste-storage canisters.

Computer models must be constructed to examine how the different substances, and possible environmental variables, would interact over time. Then, the results of the modelling exercise must be tested on site, by tunnelling and equipping cavernous galleries, while official authorisations and public support must be won.

Once operational, the repositories will be monitored for 100 years, starting from when spent fuel is first put in. Then they will be sealed for posterity. The repositories are supposed to remain hermetically sealed for at least 100,000 years – roughly the length of time human beings have existed on earth – by which time any radioactivity seeping out should be no stronger than the earth’s own background dose.

The world’s first such repository is expected to become operational in Finland in 2015, the second in Sweden in the early 2020s and the third in France in 2025. Metal canisters full of spent fuel, which will have already been cooling for years, will be fitted into concrete-lined holes in the tunnel walls. Bentonite clay, a soft medium that traps water, will be packed around the canisters to give an extra layer of protection.

As the repository is filled, it will be progressively sealed, using purified clay and concrete, tunnel by tunnel, gallery by gallery.

Cocktail of radioactive elements

France, with 58 nuclear reactors, has the world’s second-biggest atomic energy park, after that of the United States. France derives 75 per cent of its electricity from nuclear power; its nuclear plants have produced 90,000 cubic meters, or 3.2 million cubic feet, of spent fuel since 1977, when the first reactor was switched on.

France reprocesses its spent fuel, extracting plutonium and  depleted uranium from the fuel rods, a process that leaves only a residue to be disposed of as nuclear waste. This residue, with a total volume of about 14,550 cubic meters, is a cocktail of radioactive elements with different chemical properties and half-lives. Containing some of the longest-lasting isotopes, it is the most dangerously radioactive waste.

Captured in molten glass and stocked in special warehouses at reprocessing plants for 40 to 50 years while it cools, it is this brew that, under present plans, is to be sent in special containment canisters for deep disposal.

At the Andra lab here, an elevator takes eight minutes to descend 500 meters, or 1,650 feet, from the surface to the laboratory, where construction workers are drilling tunnels even as scientists monitor experiments that will run for several years. They are observing the effects of heat on the surrounding rock, the corrosion of the steel to be used for the canisters, the movement of water and radioactive isotopes through the rock, and the production of gases.

Six years in the digging, the laboratory now extends over a kilometer underground, and plans have been drafted to double its size. The proposed repository site is 3 kilometers, or 1.9 miles, away. Gerald Ouzounian, the international director at Andra, said that research had found that hard clay had a water content of just 15 per cent, and that water remained in the clay rather than moving through it. This is critical for the repository, because it must prevent radioactivity seeping out into groundwater and contaminating soil, plants, animals, and ultimately, human beings.

“The enemy is water,” Ouzounian said. “Having only 15 per cent water in clay is like not having any water at all.”

Ouzounian, a geochemist, said that studies showed the seam to be highly homogenous with little fracturing, reducing the risk of radioactivity escaping through fissures in the rock.

Clay, he added, has negatively charged ions on its surface while most radioactive isotopes are positively charged. “This is key to the design of the repository,” he said.

“The clay rock has such power of retention that if there were to be any release from the canister at any phase of the storage period, the radioactive elements would also be trapped on the surface of the minerals in the clay.”

Even after the canisters have disintegrated, which Andra expects to happen in about 4,000 years, the rock should provide an impermeable barrier, he said. “The most conservative calculations show that radionuclides cannot move more than a few meters at most over a period of the order of a million years.”

Still, such assurances cut little ice with opponents of the plan. “No geologist can guarantee that there will never be water infiltration in the places intended for storage,” said Jean-Marie Brom, a research director in particle physics at CRNS, the French national research institute, and a veteran anti-nuclear campaigner.

A Greenpeace review of research on geological repositories, published in September, listed several scientific caveats, including a lack of understanding of the multiple chemical interactions that may occur; doubts about the accuracy of computer modelling over long time scales; and the possibility of an earthquake or other disturbance to the site during the repository’s life.

“Are we really ready,” said Helen Wallace, the report’s author and a physicist who works with Greenpeace, “to say we understand enough about this option of putting it underground, which does mean at this stage of scientific knowledge crossing your fingers and hoping none of these things really do go wrong?”