In Europe, nuclear power is undergoing a revival, but the problem of how to best store highly radioactive nuclear waste is still not solved.

The most recent country to join the nuclear revival is Sweden. In February Stockholm reversed a decision from 1980 to phase out the country's nuclear reactors.

Over the past few years, Italy, the Netherlands, Belgium, Switzerland and Britain have scrapped phaseouts, extended running times of their plants or even decided to build new ones. Then there are Europe's nuclear powerhouses: Eighty percent of France's electricity is produced in nuclear plants, and Finland is currently building what will be the world's largest nuclear power plant.

Memories of major incidents at nuclear plants are fading, and countries -- including the United States -- see in atomic energy an option to become less dependent on foreign oil and save carbon dioxide emissions in the process.

While the security of modern plants has greatly improved, one key issue hasn't been solved yet: the storage of highly radioactive waste produced by nuclear reactors.

U.S. President Barack Obama recently cut funding for the controversial Yucca Mountain nuclear storage project in Nevada, arguing that there are too many questions over its safety -- a clear sign that Washington has no viable answers to the questions tied to nuclear-waste storage.

In Europe, several countries launched programs to identify possible waste-storage sites; most countries bank on geological formations, some on natural caverns like Finland and Sweden, others on decommissioned mines like Germany and Switzerland, with France planning to first reprocess its spent fuel and to then store smaller amounts in geological formations.

While Sweden is still in the process of choosing a site, with a decision expected to follow later this year, neighboring Finland is pretty far advanced in its planning. Helsinki has identified a geologic repository near two existing reactors where it aims to store waste sealed in copper-clad containers starting in 2020.

France comes in at a close second, having chosen a location in 1998 and with a working repository in place hopefully by 2025.

However, storing nuclear waste may be a bit harder than it sounds. The different types of waste radiate from 10,000 years to several million years; they would need to be sealed in repositories that are completely secure for such a period of time to avoid potentially catastrophic consequences in the case of leakage. Naturally, there exists no practical experience with such a long-term project -- and short-term experience, alas, has been quite worrisome.

Last September it surfaced that a German nuclear-waste storage site intended to simulate permanent storage was leaking, causing its security to rapidly deteriorate.

At the time, German Environment Minister Sigmar Gabriel told reporters that the dumping site in the Asse mountain range in northern Germany, which holds some 125,000 rusty barrels of nuclear waste, is "the most problematic nuclear facility in all of Europe."

Over the past decades, some 3,170 gallons of salty base had flushed into the site each day, and barrels with waste were leaking. Asse, Gabriel told German daily Bild, has "as many holes as Swiss cheese." Berlin was forced to shut down the site and has tried to come up with solutions how to save it.

Earlier this week Gabriel revealed that companies for years had dropped their nuclear waste into the site, treating Asse not as a place for temporary storage and research but for careless dumping of waste never intended to see the light of day again. Gabriel complained that companies are unwilling to help pay for the cleanup at Asse, estimated to cost at least $2.5 billion. Gabriel called for a nuclear-energy tax aimed at raising at least part of that sum.

The minister is one of the opponents of nuclear energy in Germany. But he has powerful foes: Chancellor Angela Merkel would like to reverse Germany's decision to shut off all its 17 nuclear reactors by 2021. If Merkel wins the federal elections scheduled for this fall, she will likely get her way.

([email protected])