From salt dome to nuclear repository

Date

24/03/2011

Around 1900, salt mining started on the Asse-Heeseberg mountain range north to the Harz mountains. Altogether three mines were built at that time. The Asse II mine is the only one that is still accessible today. Asse I and Asse III already drowned decades ago (meaning they were filled up with water) and had to be given up.

From 1909, the potash salt carnallitite was mined in Asse II. However, as early as in 1925, production was stopped for economic reasons. Until then, approximately 1,000,000 cubic metres of the salt rock had been mined. The humid residues from potash fertiliser production were brought back into the mine and used to backfill the chambers.

Additionally, rock salt was mined in Asse II. From 1916 until 1964, 131 chambers were mined in the mine’s southern flank, from which 3,350,000 cubic metres of rock salt were mined. In the central part of the mine, additionally 450,000 cubic metres of so-called Staßfurt rock salt were mined from 1927. The cavities that had been generated during rock salt mining were not backfilled at that time.

Radioactive waste is emplaced

In 1965, the Federal Ministry for Scientific Research and Technology (Federal Ministry for Education and Research) instructed Gesellschaft für Strahlen- und Umweltforschung (today: Helmholtz Zentrum München) to explore the disposal of radioactive waste in the abandoned Asse mine. Following corresponding reconstruction, trial emplacement of radioactive waste started in 1967.

Asse II was virtually no longer used as trial storage facility from 1971 but was used as repository for the storage of the major part of the low-level and intermediate-level radioactive waste of the Federal Republic of Germany. Altogether 125.787 drums and waste packages containing low-level and intermediate-level radioactive waste were emplaced in the mine until 1978. The radioactive waste was stored in altogether 13 chambers: Ten are located in the southern flank of Asse II in a depth of 750 metres and two in the central part in depths of 750 metres and 725 metres, respectively. Between 1972 and 1977, exclusively intermediate-level radioactive waste was emplaced in a chamber lying in a depth of 511 m.

Emplacement stopped in 1978 after the Atomic Energy Act had been amended in 1976. Now a nuclear law plan-approval (licensing) procedure was required as a condition for radioactive waste disposal. However, the Mining Law continued to be the legal basis for the operation of the Asse II mine. A decommissioning concept for the time following emplacement did not exist at that time. According to present law a decommissioning concept including proof of long-term safety is an essential condition for licensing a repository under nuclear law.

The Federal Office for Radiation Protection becomes new operator

On 4 September 2008, the Federal Ministry of Education and Research, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, and the Lower Saxony Ministry for the Environment and Climate Protection decided that the Asse II mine will procedurally be treated as a repository in the future. Therefore, the Federal Office for Radiation Protection (BfS) that is responsible for the disposal of radioactive waste was to take over the operatorship of the Asse mine from Helmholtz Zentrum München with effect from 1 January 2009. With decision of 5 November 2008, the federal cabinet cleared the way for this procedure.

On 1 January 2009, operatorship changed. Since then, BfS has been operating the Asse mine under nuclear law. Nuclear law makes greater demands on the operation, decommissioning, and radiation protection of the facility than Mining Law does. According to nuclear law, participation of the public in the plan-approval procedure for the decommissioning of the Asse mine is absolutely mandatory. Furthermore, different decommissioning concepts had to be evaluated. BfS published the result of this evaluation in January 2010.

According to the present state of knowledge, the best variant of how to further deal with the radioactive waste emplaced in the Asse II mine is retrieving the waste. Apart from the retrieval of the waste, the complete backfilling of the mine and the relocation of the waste to deeper parts of Asse were examined, too. According to the present state of knowledge, proof of long-term safety can be furnished for the option of retrieving the waste.