As a key stage in its final decommissioning, backfilling has begun of the former salt mine in Gorleben, Lower Saxony, which had been considered a possible site for geological disposal of Germany’s high-level radioactive waste.
Consideration of the Gorleben rock salt formation as a possible radioactive waste repository site started in 1977. Following government approval for underground exploration in 1983, excavation work began in 1986 with the sinking of the first of two shafts. However, in 2000, in line with plans for the eventual phaseout of nuclear power, work at the mine was suspended until March 2010. In 2014, the federal government and the government of Lower Saxony agreed that activities would be scaled back to what was required to keep the mine open. Underground areas that were no longer needed in order to keep the mine open were decommissioned and sealed off.
In September 2020, the Gorleben salt dome was withdrawn from the list of potential sites for a repository for geological reasons based on an interim report by Germany’s Federal Association for Final Storage (BGE – Bundesgesellschaft für Endlagerung). BGE and the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety & Consumer Protection (BMU – Bundesministerium für Umwelt, Naturschutz, Nukleare Sicherheit und Verbraucherschutz) then considered how to proceed and decided in 2021 that the mine should be decommissioned. The salt that was dug out for the exploration will be used to backfill it. When the construction of the shafts for the exploration mine in the salt dome began in the 1980s, the salt was transported to the surface and has since been kept in the immediate vicinity.
There are currently some 415,000 tonnes of rock salt that can used to fill the mine. This corresponds to a volume of approximately 330,000 cubic metres. The filling volume of the mine rooms is around 234,000 cubic metres and that of the shafts around 94,000 cubic metres.
In August 2023, BGE awarded a contract to dismantle the Gorleben mine and to backfill it using the salt previously removed. The tender was won by a consortium consisting of the companies Redpath Deilmann GmbH (Dortmund) and Thyssen Schachtbau GmbH Germany (Mülheim an der Ruhr).
Loaders and excavators have been delivered to the site and a road milling machine was delivered to the dump to loosen the salt. Over the years, the salt has melted through the rain and has solidified. The loosened rock salt is put into a container towed by a tractor. Four containers loaded with salt rock will be taken underground every hour. One container can hold around 15 tonnes of rock. Work will be carried out around the clock in three shifts. In the morning and midday shifts salt is transported underground and during the night shift, maintenance and repair work is carried out.
BGE estimates it will take about three years to completely fill the pit and the shafts. The site will be demolished. The complete demolition is scheduled to be completed by 2031.
The closure project consists of several phases. In Phase 1a the salt dump will be dismantled and the mine filled. The surface of the salt dump will be used for this purpose. The remainder of the salt dump will be removed in phase 1b.
Phase 2 includes the backfilling, dismantling and closure of the shafts. Possible materials for backfilling are currently being tested. The shafts were used to transport people, machines and materials underground while the mine was being developed and the salt dome explored.
In Phase 3 it is planned to dismantle the above-ground facilities and the reuse of the site as well as the final discharge from the mining supervision. BGE will be released from its responsibility under mining law and the site will be returned to the owner – the DWK (German Society for the Reprocessing of Nuclear Fuel). BGE noted it is not involved in the plans for the subsequent use of the site.
