Final storage

The Federal Government of Germany has decided to store radioactive waste in final storage facilities in ‘deep geological formations’ to keep them out of the biological cycle for as long as possible. This decision was taken because of Germany’s population density, climatic conditions and the fact that Germany has geological formations that are suitable for this purpose.

Both hot and relatively cool waste will be stored finally in deep geological formations for safety reasons.

Hot radioactive waste (from spent fuel elements) is more active, so the temperatures that radioactive waste generates are correspondingly higher. The Germans are still looking for the most suitable deep geological formations in which to store them finally.

Studies to date have shown that, highly radioactive hot waste can be safely stored finally in deep geological formations even with today’s state of the art science and technology.

Germany has approved the Konrad shaft as the final storage facility for radioactive waste producing negligible heat.

The salt stock Gorleben site is currently the most studied site for a possible final storage facility for radioactive waste producing substantial heat.

Any further investigations have been interrupted by a politically motivated moratorium since 1 January 2000, and have not resumed to date.

The radioactive waste producing substantial heat obtained at present, such as spent fuel rods, is put into storage at the nuclear power plant sites themselves in interim site storage facilities in CASTOR containers.

Other radioactive waste producing substantial heat is prepared and put into storage in glass moulds at the final storage facility in Gorleben, which is also where the waste returned from the reprocessing plants in France and Great Britain is stored.

For radioactive waste whose thermal radiation is negligible, overground interim storage facilities have been set up as collection and buffer stores and as storage facilities, as no final storage facilities are available.

From 1967 to 1978, radioactive waste producing negligible heat — then called low and moderately active waste — was stored at Salzbergwerk Asse II (experimental final storage facility) under the strategy at that time.

Before it was used as a final storage facility, Asse II worked as a salt mine for more than fifty years; the waste is stored in the chambers excavated in the course of extracting the salt. The prevailing geological conditions led to the salt formations moving and loosening, so water penetrated into the mine, which means that Asse does not fully meet the integrity and stability requirements for a final storage facility. The German Federal Office for Radiation Protection, which operated the Asse final storage facility at that time, believes that the site safety conditions at the time only exist to a limited extent today.

As far back as 2007, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety instructed the Federal Office for Radiation Protection to refit the former Konrad shaft facility at Salzgitter as a final storage facility for radioactive waste producing negligible heat. The Konrad final storage facility has natural barriers which contain the radioactive waste permanently. Above the final storage facility, there is a covering layer of clay up to 400 m thick which prevents surface water penetrating. The storage areas are between the 800 m and 850 m strata.

Nine storage areas have been approved to allow for the storage space originally applied for of 605,000 m3. As matters currently stand, two storage areas capable of holding 280,000 m3 of waste should suffice, as new conservation procedures have reduced the volume of waste involved.

Under the planning approval of 2002, the Konrad final storage facility can hold up to 303,000 m3 of radioactive waste producing negligible heat. By way of comparison: a single CASTOR container with thermally radiant waste contains more radioactivity than the entire 303,000 m3 of radioactive waste Konrad is allowed to hold.

By the time all the nuclear power plants in Germany have reached the end of their working lives, it is estimated that a total of approx. 17,000 t of heavy metals will have accumulated as spent fuel elements, that is thermally radioactive waste producing substantial heat.

Final storage facilities for highly radioactive waste could be any geologically stable ground formations such as salt stocks or rock formations. The structural engineering challenges which final storage facilities present are in particular how to build the tunnels required to access the actual storage facilities and designing the storage facilities at great depths.

image074This model is the most advanced in the world, and was developed at the nuclear power plant site at Olkiluoto, Finland, where the deepest point achieved in the rock formations is approx. 420 m. The highly active waste stored at this depth is fused into glass, and will be enclosed completely in concrete once it has cooled down to some extent.

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