The Asse is a former salt mine in Lower Saxony. From 1965 onwards, it served as a large-scale research facility to test the final storage of radioactive waste, despite warnings dating back to 1965 that the salt mine was neither watertight nor sufficiently stable. The facility was designated to store waste with low and medium-level radiation and no heat generation, and operated between 1967 and 1978.

The mine’s publicly owned operating company applied to officially close the facility in 2007. After media reports of radioactive saltwater leakages, the operator was accused of misinforming the supervising authorities, a claim that was later officially confirmed. Since 2009, the Federal Office for Radiation Protection (BfS, Bundesamt für Strahlenschutz) has operated the site, meaning the Asse mine is no longer supervised by the Federal Research Ministry but by the Federal Ministry for Environment and Nuclear Safety. In 2010 the BfS began an inventory to take stock of the radioactive waste stored in the Asse mine, finding 14,800 containers with undeclared content. The number of containers with medium-level radioactive waste had to be revised upwards from 1,300 to 16,100 and the total quantity of plutonium from 6 to 28 kilograms.

In 2010, the BfS proposed several options to safely retrieve all waste stored in the Asse mine.

• Further reading: CLEW dossier The challenges of Germany’s nuclear phase-out, CLEW factsheet The history behind Germany's nuclear phase-out
• CLEW research tour: Phasing out nuclear energy in Germany: The cost, the obstacles, the unanswered questions
• Date of publication: January 2016