Researchers are working on ways to place radioactive waste some four to eight hundred metres underground and seal it off with specialised plugs. If they succeed, the first permanent disposal sites could be operating in Europe by 2025.
Nuclear power provides about a third of Europe’s electricity, yet there are still no permanent disposal sites for the most hazardous radioactive waste.
Around 270 000 tonnes of high-level waste, mostly spent fuel, are in temporary storage around the world, according to the World Nuclear Association, an industry organisation. At the moment, the spent fuel rods are usually placed in carefully constructed vats, which are lowered into pools of water.
However, that’s problematic because they are vulnerable to natural disasters. After an earthquake and tsunami struck a nuclear power plant in Fukushima, Japan, in 2011, one of the greatest fears surrounded a water tank storing radioactive waste. If this dried up, highly radioactive spent fuel rods could have been exposed, raising the threat of a catastrophic release of radioactive materials into the atmosphere.
Researchers came together in mid-October 2013 to look at permanent solutions for the final disposal of radioactive waste during the European Commission’s EURADWASTE ’13 conference in Vilnius, Lithuania. They discussed technology being developed to construct permanent underground disposal sites known as deep geological repositories, such as a planned facility half a kilometre underground in Sweden with 65 km of tunnels. These repositories will aim to keep the waste out of reach of human beings and the wider environment for hundreds of thousands of years, until its radioactivity decays to negligible levels.
‘The goal is to have three operational repositories within the European Union within 15 years,’ said Jan Gugala, project coordinator of LUCOEX, an EU-funded project whose name is short for Large Underground Concept Experiments. One will be the planned site in Sweden, while others are planned for Finland and France. ‘We know what we want to build and we have a good idea of how this should be implemented.’
However, the technology is only one step towards disposing of the waste. ‘The easy part is finding a method,’ said Gugala. ‘The other big challenge is finding a place to build a repository. In Sweden we have locations where we are welcome, but you can find political acceptance for repositories in only a few countries.’
Dealing with nuclear waste does not just mean preventing it from doing harm today, but also ensuring that waste does not hurt future generations.
Various solutions have been studied in the past. Scientists considered placing the nuclear waste between continental plates below the ocean floor, so that it would be carried deep underground as they move over each other, however this idea was rejected because it would have been impossible to check the effectiveness of the solution.
An idea to dispose of the waste underground in Antarctica sounded promising: heat from the radioactive decay would melt ice sheets below the waste, causing it to sink. But this plan was abandoned due to international treaties aimed at preserving the near pristine state of the continent. Sea dumping – which was in the past used for lower-level, less hazardous nuclear waste – has been banned too.
That’s why research on disposing of the waste deep underground, such as that being done by the LUCOEX project, is so important. The project partners – the Swedish Nuclear Fuel and Waste Management Co (SKB) and Posiva of Finland – have been working on a concept to dispose of waste in half a kilometre of crystalline hard rock.
The concept uses three barriers to slow down the movement of the radioactive particles while the radioactivity gradually decays. First, the spent fuel will be placed in a sealed disposal canister made from a five centimetre shell of pure copper, with a lid fastened using a sophisticated welding technique that eliminates pores and cracks. Copper canisters are appropriate for this kind of bedrock because, even though it contains water, copper corrodes only very slowly in the oxygen-free environment. In addition, geologists have found copper deposits from millions of years ago, so its behaviour can be studied over the timescales needed.
Swedish and FInnish bedrock
These canisters will, according to SKB’s plan, eventually be placed in deposition holes in an underground complex of tunnels covering four square kilometres. Bentonite clay, which absorbs water and stops it getting through, will be used to hold the canisters in place, thus creating a second barrier. The third barrier will be the bedrock.
The Swedish repository should be capable of storing 6 000 canisters containing 12 000 tonnes of spent nuclear fuel, the amount that all of Sweden’s current nuclear power plants have produced and are set to produce in the forseeable future. When the underground galleries that make up the repository are full, the plan is to backfill the system with bentonite clay and seal it with a number of concrete plugs.
It’s one of several designs being examined by the LUCOEX project. It will also study horizontal disposal in different types of clay found in France and Switzerland, which are the other participants in the project.
‘The main goal of LUCOEX is to show we can construct repositories with four different concepts,’ said Gugala. ‘There are different types of waste and geological conditions in Europe. We want to show that we can do this with the technology we have today.’
Another ongoing project, DOPAS, is developing construction methods and technologies for plugs and seals to precisely seal off the repositories. MoDeRn, which was completed in 2013, developed a reference framework for monitoring activities during the various phases of radioactive waste disposal.
Contributor: Sebastion Moffett