Former salt mine and former repository for approximately 126,000 containers of radioactive waste at Remlingen-Semmenstedt, now managed by the Bundesgesellschaft für Endlagerung (BGE) as the site of a legally mandated, technically unprecedented programme t
The Schachtanlage Asse II is a former potash and rock-salt mine on the Asse ridge, ten kilometres south-east of Wolfenbüttel in the Landkreis Wolfenbüttel, Niedersachsen. The older of its two surface shafts, Schacht Asse II, was sunk in 1906; Schacht Asse I had already been sunk in the same ridge and was abandoned in 1906, and Schacht Asse III followed but was given up in 1924. Schacht Asse II served the commercial extraction of potash and rock salt from 1909 until 1964.
In 1965 the Gesellschaft für Strahlenforschung (GSF), acting for the federal government, purchased the former mine for 750,000 DM and began using it as a research facility for the underground disposal of radioactive waste. Between 1967 and 1978, approximately 125,787 containers — representing around 47,000 cubic metres of low- and intermediate-level radioactive waste — were emplaced in thirteen former mining chambers on the 511-, 725-, and 750-metre levels. Many containers were already damaged at the point of emplacement.
Research into high-level waste disposal in salt continued until 1995. Saltwater infiltration and serious structural instability — consequences of the intensive historical salt extraction — progressively undermined the integrity of the installation. In 2008 it became publicly known that radioactively contaminated salt solutions had been pumped to the 975-metre level without radiation-protection authorisation.
The Bundesamt für Strahlenschutz became operator in 2009 under nuclear law. In 2013 the Bundestag passed the Lex Asse, legally mandating retrieval of all radioactive waste and the subsequent decommissioning of the mine. The BGE, which took over as operator in 2017, plans to retrieve the first containers no earlier than 2033.
Retrieval costs are estimated at four to six billion euros.
The Schachtanlage Asse takes its name from the Asse ridge, a low hill in the Landkreis Wolfenbüttel rising to approximately 240 metres. The geological structure below the ridge is a salt stock of Zechstein origin. Two shaft installations were developed to exploit the potash and rock-salt deposits beneath it.
Schacht Asse I was already being worked and was abandoned in 1906. Schacht Asse II — to which the complex's common name refers — was sunk from 1906; after sinking was complete the shaft was used for commercial extraction of potash and rock salt from 1909. During the operational period the extraction chambers were mined with the intensity typical of the German potash industry, which left the rock mass perforated with large open voids. Commercial extraction continued until 1964. Schacht Asse III was a later addition but was abandoned in 1924. The abandonment of Asse I and III for water ingress — both had become flooded with water after closure — was later considered significant context for the long-term behaviour of the salt stock as a whole.
In 1965, the GSF (Gesellschaft für Strahlenforschung), acting on behalf of the federal government, purchased the salt mine for 750,000 DM and established the Institut für Tiefenlagerung radioaktiver Abfälle, intended to research and demonstrate the permanent underground disposal of radioactive waste in a salt formation. Because the Federal Republic was preparing to enter large-scale commercial nuclear power generation and needed a disposal route for the resulting radioactive waste, the dry and geologically stable conditions in the salt were considered an ideal environment.
Between 1967 and 1978, approximately 125,787 containers of low- and intermediate-level radioactive waste, representing about 47,000 cubic metres, were emplaced in thirteen former extraction chambers. Two chambers lie at 725 metres depth in the middle section of the mine, ten chambers lie in the southern flank at 750 metres depth, and a further chamber is at 511 metres. The waste came from nuclear power stations, research institutions, and industrial users across the Federal Republic. From 1967 to 1975, no charges were levied for the emplacement of approximately half the containers; from December 1975, tariffs of 150 to 3,700 DM per container were charged. In total, 16.5 million DM was collected. Emplacement methods were progressively degraded over the three phases of operation: containers were initially placed upright on one another, then tipped on their sides, and finally dropped from a height down salt slopes into the chambers, with known damage to containers accepted from this point. Retrieval was explicitly not planned. In 2009 it was publicly revealed that approximately 29 kilograms of plutonium had been emplaced — substantially more than the 9 kilograms previously disclosed.
Following the end of waste emplacement in 1978, research into the geological and engineering aspects of disposing of highly radioactive waste in salt continued at the Schachtanlage Asse II until 1995. Remaining open voids from the historical salt extraction were backfilled between 1995 and 2004. In 1997 the federal government decided to close the shaft under mining law (Bergrecht), using solid fill as the intended closure method.
From 2005 to 2008, radioactively contaminated brine solutions were pumped from their collection points to the 975-metre level without the legally required radiation-protection permit. When this became publicly known in mid-2008, the federal government reversed the closure strategy and resolved instead to close the mine under nuclear law (Atomrecht). On 1 January 2009 the Bundesamt für Strahlenschutz (BfS) became the new operator. An analysis of closure options in 2010 concluded that only retrieval of the radioactive waste could satisfy the legally required demonstration of long-term safety. The Lower Saxon Landtag voted for retrieval in 2012, and in April 2013 the Bundestag passed the Lex Asse — the Gesetz zur Beschleunigung der Rückholung radioaktiver Abfälle und der Stilllegung der Schachtanlage Asse II — with a broad parliamentary majority, legally mandating retrieval before final decommissioning.
On 25 April 2017 the Bundesgesellschaft für Endlagerung mbH (BGE), a wholly state-owned company, became the operator, taking over from the BfS. The BGE published its retrieval plan in April 2020. The plan requires sinking a new shaft (Schacht 5) and constructing horizontal connection roadways to allow access by more workers and larger equipment, together with a waste treatment facility and an interim storage site near the Asse. Saltwater infiltration continues: the principal inflow collection point registered approximately twelve litres per hour in 2008; by 2024 the rate at the main collection level had decreased, but water was being intercepted in greater quantities in deeper zones above the emplacement chambers. The Entsorgungskommission assessed in a 2020 report that the timescales for planning, approval, and implementation are demanding, that reliable information about the condition of the emplacement chambers and the containers is lacking, that many containers are severely damaged, and that significant radiation exposures for workers and nearby populations must be anticipated over the decades of retrieval. The first containers are not expected to be retrieved before 2033. Final decommissioning is projected for the 2050s–2060s. Remediation costs are estimated at four to six billion euros; these are to be borne by the federal government, not the waste producers. An information centre (Infostelle Asse) near the mine entrance provides public exhibitions and lectures on the retrieval programme.