Rock salt, at least while it's underground, has two main properties: It can be soft and easy to mine, and it can form a watertight seal. This helps explain why the West German government started forklifting thousands of metal drums of "low-to-medium" radioactive waste into an abandoned salt mine called Asse II during the 1960s.
Asse II is named after its mountain range in the state of Lower Saxony. The mine plunges deep into the hills near Braunschweig (aka Brunswick), in the center of Germany, and politicians in Bonn regarded it during the Cold War as a test site for storage of nuclear waste. An overhead layer of rock salt would shield the mine from groundwater, and the shifting salt itself, over centuries, would seal up any fractures and finally pack the nuclear waste in a safe geological bed.
But that's not what's happening.
Around 12,000 liters of groundwater leak into the mine every day. Some of it mixes with the radioactive waste. A few weeks ago, the Federal Office for Radiation Protection (BfS) finally admitted that some brine collected in Asse II had traces of tritium and caesium 137.
But last year the German public learned that the group in charge of maintaining Asse II at the time had known about the accumulation of suspect water since 2005 — and even tried to mitigate the threat to its employees by pumping it to a deeper level of the mine. Heinz-Jörg Haury, spokesman for the Hemholtz Institute for Scientific Research, tried to explain in mid-2008 why Helmholtz had made no public announcement. "We believed no one was in danger, inside or outside the mine," he said.
The public outrage led German politicians to take the mine out of the Helmholtz Institute's hands and place it under the BfS. But Asse II has also leaked groundwater since at least 1988 — meaning, at the very least, that decades of Cold War research conducted there failed to solve some of the most basic problems of nuclear storage. Sigmar Gabriel, Germany's environment minister, has called the mine "the most problematic nuclear facility in Europe." Experts say chemical reactions between the brine and the radioactive waste could soften the salt rock and lead to a partial collapse of Asse II by 2014.
No doubt Asse II has been mismanaged, and some lessons from the "research facility" have been learned. Along with 120,000-odd barrels of radioactive slop, according to a report last year, highly radioactive plutonium waste and even a few spent fuel rods were dumped in the mine.
"The standards that were set [in the early days of Asse II] would be completely unacceptable today," said a state environment minister for Lower Saxony, Stefan Birkner, to a TV news reporter in 2008. But the debacle has reawakened anti-nuclear sentiment in Germany. Asse II was supposed to be impermeable for tens of thousands, if not millions, of years.
American salt storage facilities are generally in better shape. James Conca, a geophysicist at New Mexico State University, likes to hand out little bags of salt rock mined from the impressive Waste Isolation Pilot Plant deep under the New Mexico desert. The salt crystals contain bubbles of water from a Paleozoic sea. "Permeability is not just very low but zero," he told a reporter from Scientific American.
WIPP, like Asse II, contains no waste from nuclear power plants, but its safety record is so impressive that Conca sees it as an alternative to Yucca Mountain for future fuel rod storage. Yucca Mountain, of course, looked good to the Bush administration in 2002, but less good to a federal appeals court two years later, which said the government had failed to prove that spent fuel rods would be safe under the Nevada desert for up to a million years.
But it's hubris for a government to think it can safely store nuclear waste beyond the lifetime of the government itself. The trouble with Asse II has been a chastening example. Political promises, stern-sounding policies, and even scientific assessments from 1989 (which said the mine had no leaks) all proved to be as full of holes as the mine itself.
Right now the radioactive brine in Asse II lies almost a kilometer below the surface of the earth, far from the "biosphere," where people live. It hasn't contaminated drinking water. It hasn't bubbled up into anyone's yard. But the mine may have to be sealed with concrete or clay — or even, oddly, flooded (with water and certain taming chemicals) — before it collapses. What happens in 500 years will then be hard to predict.
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