Preparing for eternity

The orange building at Covra is a temporary housing for the Dutch high level radioactive waste

A new European Union directive requires member states to devise plans for the long-term storage of radioactive waste. TU Delft wants to be involved in designing the Dutch solution.

The policy of most EU member states for long-term storage of high-level nuclear waste has so far mainly consisted of setting up intermediate storage facilities and postponing plans for definitive repositories. But after more than fifty years of nuclear energy in Europe, and with the prospect of growth in the sector, the European Commission has decided to put pressure on member states to come up with solutions for storage into infinity. With 7,000 cubic metres of high-level waste produced annually in Europe, interim storages cannot last forever.

“The EU needs to press forward to underpin a secure electricity supply system,” observes Dr Russell Alexander, of the Swiss-based ITC School of Underground Waste Storage and Disposal. Dr Alexander agrees with the EU Directive that there is consensus among scientists and the International Atomic Energy Agency (IEAE) that geological disposal “is the best technical solution today and for the foreseeable future”. So, underground it is.
In the Netherlands, the central organisation for nuclear waste, Covra, coordinates the research programme Opera, which studies the final repository of nuclear waste. The programme will research possibilities of storage in salt and clay layers, which are abundant in the Dutch underground. Covra’s deputy director, Dr Ewoud Verhoef, expects to have a research plan in place by June. The programme is worth ten million euro over five years.

Professor Michael Hicks (Civil Engineering and Geosciences), a soil mechanic specialist, is waiting for Covra to send out a call for research proposals. His proposals will concern the geomechanical research of the boom clay layer (at a depth of about 500-metres) and the feasibility of constructing tunnels and shafts in this clay. In addition to TU Delft, the universities of Wageningen and Utrecht, as well as TNO, are expected to submit research proposals.
A 1,000 Megawatt nuclear power plant annually produces 25 tonnes of spent fuel, of which most consists of uranium (24 tonnes) and plutonium (250 kilograms), which are both then recovered and recycled in a nuclear fuel programme. The remaining 750 kilograms consists of high-level nuclear waste that is usually molten in glass (‘vitrified’) and stored in temporary deposits.

Over the first 50 years the waste loses about 90 percent of its radiation and heat production. Thus, even if geological storage were available, it would still be a good idea to let the waste cool down for half a century. Subsequently, the waste needs another 5,000 years to reach the radiation level of uranium ore.  Uranium and plutonium, accounting for 96 percent of the spent fuel, need even longer (300,000 years) to reach that level of activity. What’s more, the material should be stored in such a way that it can be retrieved in case the evasive new nuclear technology of fast reactors becomes available. This new generation of reactors should be able to process the presently unusable uranium-238 into plutonium-239, which can then be used as nuclear fuel.

Of the European Union member states, Finland, Sweden and France have the most advanced programmes for developing nuclear end repositories. Following geological research into clay layers, France has now designed an underground nuclear storage facility made of tunnels and shafts built in clay. Meanwhile, near the Finnish village of Eurajoki, the construction of the Onkalo repository in granite rock is ongoing. In a James Bond-like setting a tunnel will descend 400 meters deep into the rock, where the radioactive waste will be stored in copper or steel containers in long, horizontal tunnels, which will be sealed with a concrete plug, several meters thick, for eternity.