Nuclear power stations have been churning out radioactive waste for decades. At least 10 new reactors came online last year - making the question of long-term storage all the more pressing. There's no solution in sight.
In 2016, 10 new nuclear reactors went online - and two more in the first half of 2017, according to the 2017 World Nuclear Industry Status Report published Tuesday. Six of these new nuclear power plants are based in China, which now ranks third on the list of the "big five" nuclear generating countries after the United States and France.
The big five make up 70 percent of the world's nuclear energy, while the US and France account for almost half of global nuclear energy generation.
In this time period, only four reactors were shut down.
As nuclear reactors continue to go online, the question of what to do with nuclear waste becomes all the more pressing - and still hasn't been answered properly.
In September this year, Germany begins the search to find a final storage solution for nuclear waste. A special commission is to scour the country for a suitable geological site to build a deep repository, where it can bury the toxic legacy of decades of nuclear power production - once and for all.
The government aims to find a site by 2031. But critics are skeptical it will meet the deadline.
There are complex technical questions over whether clay, granite or salt might provide the best protection against leakage or contamination. The site has to be secure for a million years - so scientists have to be sure it will survive eventualities such as future ice ages.
But just the biggest challenge will be to persuade communities to accept a nuclear waste dump on their doorstep.
Four decades of resistance at Gorleben
In the late 1970s, West Germany chose a salt site at Gorleben in Lower Saxony for exploration as a possible final nuclear waste repository. A decades-long battle ensued, with locals vehemently protesting against the project.
Protestors long argued that Gorleben, a sparsely populated area close to the East German border, was selected for political rather than scientific grounds.
Technical questions were also raised.
Science vs. politics
US nuclear expert Robert Alvarez says at least Germany has a well-defined set of scientific criteria to select a site that will be geologically stable and protect the waste in barrels from oxidation, and therefore corrosion.
"I think the German government has been paying more attention to the geologists and to the nuclear safety people," Alavarez, an associate fellow at the US Institute for Policy Studies, told DW.
In the United States, President Donald Trump has been making moves to restart work on a repository at Yucca Mountain, a former nuclear weapons test site in the remote Nevada desert.
Alvarez describes the selection of the site ahead of the 1988 election as the result of a political move by Congress, which scrapped a survey of various locations around the US.
"People went crazy - and it scared all the politicians who were running for election," Alvarez explains. "So by 1987 when the process was unfolding, Congress just changed the law, and said: 'We're going to put it in Yucca Mountain, all you guys are off the hook.'"
He points out that the site was already contaminated from nuclear testing, and that Nevada has just one electoral college vote. But he says geological conditions at Yucca Mountain are far from ideal, and would require large-scale ventilation for at least 100 years to keep the waste cool.
"There is a lot of baloney about it being scientifically the best site," Alvarez says. A granite site, like those being explored in Finland and Norway, would be far more suitable, he says.
"We have quite a lot of granite geology in our country but it happens to be in populated areas," Alvarez added.
Scandinavia leading the way
Finland has made headlines with what has been lauded as the world's first final long-term nuclear waste repository, 400 meters deep in the granite bedrock off the country's west coast. A similar project is underway in Sweden.
Alvarez says these Scandinavian countries are very much leading the way. But can we really be sure that these deep granite repositories will be safe in hundred of year, as Finland intends?
"To put it mildly, that claim contains strong elements of speculation," Alvarez says. "How can we predict what the world will be like even 100 years from now?"
And other countries face bigger challenges.
Repository plans collapse around the world
"The problem in Finland and Sweden is dead simple," says Andy Blowers of independent expert group Nuclear Waste Advisory Associates. "You have one type geology, and lots of it - you've got very few power stations, and so a defined amount of waste."
France, which gets three-quarters of its electricity from nuclear, planned to open a repository at Bure in eastern France by 2030.
Finland locks away nuclear waste
But, like Yucca Mountain, it has been beset by technical problems and safety concerns, and protestors are campaigning against the project.
In the United Kingdom, plans for a repository located close to its Sellafield decommissioning and reprocessing site were scrapped following public and scientific consultation.
And authorities in South Australia abandoned publically unpopular plans for an international repository that would take nuclear waste from around the world.
Waiting for a solution
So, with even Finland yet to begin loading its repository, what's happening to all the waste generated over the more than six decades we've been powering out economies with atomic energy?
For the most part, it's sitting around - above ground, in temporary and interim storage facilities with widely varying levels of security, which were never intended to store so much waste, for so long.
Alvarez says Germany is, again, managing better than most. For one thing, Germany was using casks that are Mercedes models compared the United States' old Chevys, he said. They are far thicker and can safely contain waste for longer.
Wet storage threatens disaster
There is a big difference between wet and dry storage. Nuclear waste has to be cooled in liquid. But if the liquid evaporates, spent fuel quickly heats up - and could result in fires with consequences experts say would dwarf Chernobyl.
When the Fukushima accident occurred in 2011, a pool containing a spent reactor was badly damaged and such an accident briefly arose as a possibility.
In fact, a leak refilled the pool. Without this happy accident, tens of millions of people - perhaps as much at 27 percent of Japan's population, according to some experts - would have had to be evacuated.
And yet, despite the dangers, countries including France, the UK, Korea and the US are storing nuclear waste in pools well after experts say it should have been put into dry cask storage.
Experts say the most pressing problem is not finding sites for final repositories, but ensuring that intermediate storage is safe - and will continue to be safe for as long as it takes to solve the riddle of how to get rid of humankind's most toxic garbage.
"I suspect that what we are going to be looking at over time is that there's going to have to be a great deal longer period of surface storage," Alvaraz says.
Mycle Schneider, an independent nuclear policy analyst and lead author of the annual status report, is not convinced geological storage should even be the ultimate goal, and that waste should be retrievable in case we find a better way to deal with it.
For time being, he says, it's a matter of finding the least-bad solution.
"It's very clear," Schneider told DW. "Take spent fuel out of the pools as quickly as possible and into dry storage, even if that storage might not be ideal to begin with. Then you get to next stage, which is an appropriate building, and then into hardened storage, like a bunker.
"And from there, you can begin to think about eternity."