It seems impossible, yet it must be: nuclear waste stored in such a way that safety is guaranteed for hundreds of thousands of years. Under pressure from European legislation, the Netherlands has also launched a research programme.
The descent takes seven minutes. Everyone is packed tightly together in the narrow, steel elevator – all wearing boots, fluorescent jackets and light-mounted helmets, as well as carrying breathing equipment on their backs and alarms on their belts that sound should the wearer collapse. Spokesman Marc-Antoine Martin has wrapped a scarf five times around his neck as protection against the draught in the tunnel. “Only research is done here,” he shouts over the noise of the cables and pulleys. The underground laboratory will never actually be used for storing nuclear waste, although the locals living in this sparsely populated area of north-eastern France find that hard to comprehend. “You’ve been working on this for fifteen years already. Et alors, you still haven’t stored anything yet?” Martin is asked in a neighbourhood café.
In the Netherlands, too, construction of a final repository for radioactive waste (see box) is now a major issue. The European Commission is pressuring member states to develop solutions for dealing with this waste. Every year another 7000 cubic metres of high-level radioactive waste is produced – enough to fill three swimming pools. Production has been ongoing for fifty years and more nuclear power plants are planned. Consequently, by 2014 the European Commission wants all member states to have plans detailing how and where the waste will be stored, how much it will cost and who will pay for it.
In the Netherlands, Covra in Vlissingen has been charged with conducting a fiveyear, €10 million euro research programme known as Opera (a Dutch acronym for ‘Radioactive Waste Final Repository Research Programme’). Research institutes and universities are invited to submit proposals. Covra’s deputy director, Dr Ewoud Verhoef, expects the research programme to be complete by June.
At TU Delft, geo-technologist Professor Michael Hicks (Civil Engineering and Geosciences) hasn’t yet received a call for research proposals, but if it comes he will propose studying the feasibility of constructing a final repository at a depth of 500 m in the Boom clay formation. It all starts with samples, which must first be extensively studied, explains his colleague, Dr Dominique Ngan-Tillard.
Storage in clay
In anticipation of the proposals, a final repository in clay strata seems to be the most likely option. The Netherlands does not have the option of using granite, as in Finland, and ever since the debacle in the German Asse region, storage in salt strata has had a bad reputation. Starting in 1967, radioactive waste was stored in an Asse salt mine, but major leaks and the danger of contaminated groundwater led to the mine’s closure. There are 126,000 casks of low- and medium-level radioactive waste there, some of them partly rotted. Storage in clay strata is already being researched in Switzerland, Belgium and France.
Indeed, the French are engaged in a major programme. Close to the village of Bure, near Nancy, a fenced-off complex has been built that includes offices, facilities and an exhibition centre. But the real business takes place in the complex consisting of 1000 metres of tunnels some 500 metres underground. Two huge shafts provide access to the complex. The construction cost €600 million and the annual research budget involves an additional €100 million. The entire complex is equipped with more than 4,000 sensors to record temperature, pressure and movements. So far, the French have invested around €1 billion in the project. The research body, Andra, which manages the lab, owes its existence to a law introduced in 1991 establishing a research programme devoted to finding a solution for the final storage of medium-level and high-level radioactive waste. French energy giants EDF and Areva are funding 95% of the programme.
“We did not know how the clay would react,” explains Martin. The oldest parts of the tunnel (dating from 2000) have steel walls supported by trusses. “We didn’t know whether the trusses should be positioned at intervals of 40, 60 or 80 cm.” There is a lot of experience of mining in coal strata, but the heavy clay in the Callovo-Oxfordian formation is something altogether different. Initially, the main focus was on what is known as convergence. Clay has a tendency to converge during excavation as a result of the pressure from the strata above. Hundreds of measurement points have been built into the walls to chart consolidation and distortions. An automated theodolite tirelessly scans the tunnels. During construction, the French took extensive advice from their Belgian counterparts at Euridice, an alliance between Niras (national institution for radioactive waste and enriched fissile materials) and the nuclear energy study centre SCK.CEN. Since the early 1980s, they have been operating the underground laboratory Hades (high activity disposal experimental site), which is situated just over the Dutch border at Mol, 250 metres underground in the Boom clay. This is a layer of clay that is around 100 metres thick, becoming thicker and deeper the further north you go. The fact that the clay is moist and plastic can be seen from the traces of water in the tunnel and the clay protruding inwards through holes in the walls.
Radiation level
The key question concerns the spread of radioactivity and the health risks this entails for generations far into the future. This is also the focus of much of the research. Clay contains water, but how quickly is it displaced? For example, the Belgians have measured the water permeability in a drill hole 10 metres deep at the end of the tunnel. Radioactive-labelled water was placed within it. Based on its spread, they were able to determine that water needs 50,000 years to spread through 40 metres of clay. But this does not apply for all the substances dissolved in the water, says Sarah Dewonck, who is coordinating the Andra experiments. Positive ions bind to the negatively-charged surface of the clay.
As a result, uranium and plutonium becomes strongly bonded to the clay. The opposite applies to negative ions, such as chlorine and iodine, which do not bond and can therefore migrate. Efforts are also being made to ensure that the radioactivity remains encapsulated for as long as possible. This requires detailed knowledge of the chemical interaction between clay, glass, concrete and steel under the influence of high temperatures and radiation levels. Research is also being conducted into this in the laboratories. Another key factor involves changes in the clay layer caused by the construction of the tunnel and by heat. Is there not a risk that this will increase the porosity of the clay and create fissures, accelerating the anticipated transport of water? This is another area both laboratories are studying by heating a tunnel up to 90 °C for a ten-year period and then analysing the results. Greenpeace refuses to be reassured and points to the dangers of accelerated corrosion, irregularities in the clay strata and the layers containing drinking water above and beneath the Boom clay. Euridice director, Dr Peter de Preter, responds: “We are talking about protection over an extremely long period, up to the point at which the radioactivity has already dissipated to a large extent. According to our knowledge and calculations, radioactivity originating from the repository will contribute at most an additional one percent to the annual natural radiation levels, and only then after many tens of thousands of years. But after hundreds or thousands of years, this level will in any case be equal to zero.” When asked what they would recommend to their Dutch colleagues, both the French and Belgian researchers say: start with a ground survey. Because just as the ground is different everywhere, the same is true for the best imaginable final repository for nuclear waste. The scope of the research is enormous, involving geology, hydrogeology, materials science, simulations and modelling, risk management and social acceptance. It would be extremely strange if TU Delft did not want to be a part of that. (JW)
