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The Asse II mine (Schacht Asse II) is a former
salt mine Salt mining extracts natural salt deposits from underground. The mined salt is usually in the form of halite (commonly known as rock salt), and extracted from evaporite formations. History Before the advent of the modern internal combustio ...
used as a
deep geological repository A deep geological repository is a way of storing hazardous or radioactive waste within a stable geologic environment (typically 200–1000 m deep). It entails a combination of waste form, waste package, engineered seals and geology that is suited ...
for
radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
in the
Asse Asse () is a municipality located in the Belgian province of Flemish Brabant. It comprises the towns of Asse proper, Bekkerzeel, Kobbegem, Mollem, Relegem and Zellik. Asse is also situated in the Pajottenland. As of 2020, Asse had a total popula ...
Mountains of
Wolfenbüttel Wolfenbüttel (; nds, Wulfenbüddel) is a town in Lower Saxony, Germany, the administrative capital of Wolfenbüttel District. It is best known as the location of the internationally renowned Herzog August Library and for having the largest c ...
,
Lower Saxony Lower Saxony (german: Niedersachsen ; nds, Neddersassen; stq, Läichsaksen) is a German state (') in northwestern Germany. It is the second-largest state by land area, with , and fourth-largest in population (8 million in 2021) among the 16 ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
.


History

The Asse II mine was developed between 1906 and 1908 to a depth of . Initially extracting
potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
, the mine also produced
rock salt Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pi ...
from 1916 to 1964. Potash production ceased in 1925. Between 1965 and 1995, the state-owned
Helmholtz Zentrum München Helmholtz Zentrum München Deutsches Forschungszentrum für Gesundheit und Umwelt (GmbH), also known as Helmholtz Munich, is a member of the Helmholtz Association of German Research Centres. It was founded in 1960 and is a joint venture by the Fede ...
used the mine on behalf of the Federal Ministry of Research to test the handling and storage of radioactive waste in a repository. Between 1967 and 1978 low-level and intermediate-level radioactive waste were emplaced in 13 chambers in the Asse II mine. Two chambers are located in the middle part and ten in the southern flank of the mine at depths from below surface. Between 1972 and 1977, exclusively medium-level radioactive waste was emplaced in a chamber on the level. Research was stopped in 1995; between 1995 and 2004 cavities were filled with salt. After media reports in 2008 about brine contaminated with radioactive
caesium-137 Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nucl ...
,
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
and
strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...
, politicians accused the operator, Helmholtz Zentrum München – German Research Center for Environmental Health, of not having informed the inspecting authorities. On 8 September 2008, the responsible ministers of Lower Saxony and the German government replaced the operator with
Bundesamt für Strahlenschutz The Bundesamt für Strahlenschutz (BfS) is the German Federal Office for Radiation Protection. The BfS was established in November 1989; the headquarters is located in Salzgitter, with branch offices in Berlin, Bonn, Freiburg, Gorleben, Oberschle ...
(BFS) - the Federal Office for Radiation Protection. In April 2017, operator responsibility for Asse II was transferred from BFS to the Supervisory Board of the Bundes-Gesellschaft für Endlagerung mbH (BGE), under the
Federal Ministry for the Environment, Nature Conservation and Nuclear Safety The Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (german: Bundesministerium für Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz, ), abbreviated BMUV, is a cabinet-level min ...
.


Inventory

Asse II contains intermediate radioactive waste (LILW-LL, Long lived) and
low level waste Low-level waste (LLW) or Low-level radioactive waste (LLRW) is nuclear waste that does not fit into the categorical definitions for intermediate-level waste (ILW), high-level waste (HLW), spent nuclear fuel (SNF), transuranic waste (TRU), or ce ...
(LILW-SL, Short lived), defined as waste without significant heat generation. After public speculation about the presence of radioactive
high level waste High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms: * First and second cycle raffinate and other waste streams created by nuclear reprocessing. * Waste formed by vit ...
in the mine the old documentation was once again reviewed in August 2008: # 125,787 drums of low level radioactive waste stored from 1967 to 1978 in various chambers at the level. The containers are mostly drums with volumes from or concrete vessels. The declared total activity at the time of storage was 1.8·1015  Bq. Around 50% of the containers came from the former
Forschungszentrum Karlsruhe The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public university, public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT wa ...
nuclear reprocessing Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...
plant, 20% from
nuclear power plant A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a electric generator, generato ...
s and 10% from the former
Jülich Research Centre Jülich (; in old spellings also known as ''Guelich'' or ''Gülich'', nl, Gulik, french: Juliers, Ripuarian: ''Jöllesch'') is a town in the district of Düren, in the federal state of North Rhine-Westphalia, Germany. As a border region betwe ...
. The containers typically included mixed and laboratory waste, rubble, scrap, filter residues and combustion residues. Liquids such as evaporator concentrates, sludges, oils, resins and solvents had to be bound as solids. According to some former employees barrels of liquid waste were accepted in the early days of storage.
Schachtanlage Asse – Befragung früherer Mitarbeiter
''. Helmholtz Zentrum München, 2008.
# 1,293 containers with medium-level radioactive waste stored from 1972 to 1977 in Chamber 8a at the level. Only roll drums were permitted with waste fixed in concrete or bitumen. The declared total activity at the time of storage was 2.8·1015  Bq. About 97% of the packages (over 90% of the total activity inventory of Asse II) originated from the Karlsruhe reprocessing plant. Some of the Karlsruhe drums contained waste from the reprocessing plant itself, and thus
fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...
material. Storage limits per drum were U-235, U-233 and Pu-239. These limits were not reached. Maximum values per drum were
U-235 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists ...
, Pu-239 and less than U-233 on the level. However the type of the waste was determined by the measurable amount of radiation outsided of the container, not by the actual contents of the vessel. Because of this it must be assumed that the containers with concrete shielding also contained medium level waste, raising their number from 1293 to 16.100. Some of these concrete vessels emitted radiation above the permitted level and had to be stored in special metal shielding. Other notable waste that is stored in the mine are 497 kilogram
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
, mercury, tons of lead and animal carcasses from radiation experiments. Even some human remains and waste from the
Nazi era Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
are rumored to be part of the inventory.


Storage methods

In the first years of operation the barrels were stored in orderly rows and space was left so it was theoretically possible to inspect them. In the later years, when most of the waste was brought in, the drums were rolled off a salt embankment into the chambers and the layers covered by salt. This was done to reduce radiation exposure of the workers and to save time, however it meant that many containers would be damaged already at the time they were stored. The waste containers were only intended to be safe during transportation to the facility. They don't have long time stability and rust after some years, especially in a salty environment. The salt surrounding them was intended to be the only containment for the waste. There never was an intention for the waste to be recoverable.


Instability of the mine

Typically salt mining is structurally unsupported. Stresses produced in the remaining salt structure during construction of the mine voids are accommodated in the overlying rock.
Plasticity Plasticity may refer to: Science * Plasticity (physics), in engineering and physics, the propensity of a solid material to undergo permanent deformation under load * Neuroplasticity, in neuroscience, how entire brain structures, and the brain it ...
effects are taken into account as they occur naturally in
salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using ...
s. Significant mechanical stress is built up between the surrounding
diapir A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
and the mine construction. The overlying rock mass in Asse II moves per year, undermining the strength of the mine construction. Because of the large number of tunnels and chambers, and the decades of use, deformation in Asse II has reached a state where the pressurised surrounding salt is losing its stability: "The supporting construction is softening by creep deformation, plasticity effects and local fractures from ground pressure." In 1979 a report on the stability of the mine was released by a working group under HH Juergens, which describes an imminent scenario of uncontrolled plastic flow from the surrounding rock on the southern flank resulting in the subsequent loss of the load carrying capacity. The manager of Asse II in 1979 and his advisers categorised this report as "unscientific" and declared that there were no stability problems. In 2007 the Institut für Gebirgsmechanik (IfG) in
Leipzig Leipzig ( , ; Upper Saxon: ) is the most populous city in the German state of Saxony. Leipzig's population of 605,407 inhabitants (1.1 million in the larger urban zone) as of 2021 places the city as Germany's eighth most populous, as wel ...
, which had been monitoring Asse II since 1996, predicted that an increase in the rate of loss of load carrying capacity would result in an increased displacement of the surrounding rock. The shifts would lead to an uncontrollable increase in water inflow and make continued dry operation impossible.


Recovery and closure

First plans for a permanent closure were developed between 1992 and 2007. Recovery of waste was not considered feasible. During this time many cavities of the mine were filled with salt as an intent to stabilize it. To fill all cavities it was planned to fill the mine with a magnesium chloride solution. However the long-term safety of this method could not be proven. The radioactive waste would have been dissolved by the solution and would have had the potential to contaminate the groundwater. The magnesium chloride solution would also have reacted with the cement which could have created explosions and blowouts of radioactive waste to the biosphere. During this time most of the caverns with nuclear waste were sealed behind thick walls; because of this the condition of the waste inside is unknown. The only theoretically accessible chamber is one with medium level waste.


Current progress

After the controversies about the facility became public and the operator was changed to the Federal Office for Radiation Protection, a new plan was developed in 2010. It became obvious that the recovery of the waste is necessary for long-term safety. The waste is planned to be collected by remotely controlled robots, sealed in safe containers, and stored temporarily above ground. Preparations include creating a new shaft that will be big enough and building the above ground storage facility. The estimated costs for the closure of the mine are estimated to be at least 3.7 billion Euro. The recovery of the waste and closure of the mine will be paid with tax money, not by the operators of the German nuclear plants, even though most of the waste was created by them. The beginning of the recovery is planned to start in 2033 and is estimated to last for decades. Chamber 7 is designated to be the first one for recovery. It contains low and medium level waste covered by salt. Test drillings in 2017 offered the first pictures from inside the chamber since decades, they show damaged and rusted containers.


Water inflow

A significant inflow of water and a subtle loss of mechanical stability may jeopardise the underground mine integrity – the site is in danger of collapsing and becoming flooded. For the period 1906 to 1988, when Asse II was an operational salt mine, there were 29 documented water breaches. They were sometimes successfully sealed off, partly dry or sometimes with negligible inflows (less than per day). Between 1988 and 2008 32 new entry points were recorded. In 1996, the BFS notified the Bundesumweltministerium that there was a risk of severe
radioactive contamination Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirab ...
if the mine ran full of water and that further investigation was urgently required. Most of the brine influx is concluded as coming from the
diapir A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
in the southern part of the mine. The brine is captured before it comes in contact with the storage drums, at the levels and, since 2005, at the level. The 2008 influx was per day. The liquid is tested for the radionuclide
caesium-137 Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nucl ...
. All measured values have been below the detection limit. The liquid is also tested for tritium. The weighted mean concentration is about 100 Bq/litre, which is the value that must be present in accordance with the European drinking water standard (and slightly more than radon levels in
Bad Gastein Bad Gastein (; formerly ''Badgastein''; Southern Bavarian: ''Bod Goschdei'') is a spa town in the district of St. Johann im Pongau District, St. Johann im Pongau, in the Austrian state of Salzburg (state), Salzburg. Picturesquely situated in a hig ...
radon spa in
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
). The brine is pumped into a tanker and transported to the abandoned K+S AG mines (
Bad Salzdetfurth is a town on the banks of the River Lamme in the district of Hildesheim, in Lower Saxony, Germany. Geography The municipality includes the town itself, and 12 civil parishes (''Ortsteile'') which were incorporated in 1974: * Bodenburg * Brein ...
, Adolfsglück and Mariaglück) The brine in Mariaglück is also tested for
caesium-137 Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nucl ...
and
tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
.


See also

*
Gorleben salt dome The Gorleben salt dome is a proposed deep geological repository in a salt dome in Gorleben in the Lüchow-Dannenberg district in the far north-east of Lower Saxony for low-, medium- and high-level radioactive waste. Site selection At the end of ...
*
Morsleben radioactive waste repository The Morsleben Radioactive Waste Repository (German: Endlager für radioaktive Abfälle Morsleben-ERAM) is a deep geological repository for radioactive waste in the Bartensleben rock salt mine in Morsleben, Börde District, in the federal state of ...
*
Nuclear decommissioning Nuclear decommissioning is the process whereby a nuclear facility is dismantled to the point that it no longer requires measures for radiation protection. The presence of radioactive material necessitates processes that are potentially occupat ...
*
Schacht Konrad The pit Konrad (Schacht Konrad) is a former iron ore mine proposed as a deep geological repository for medium- and low level radioactive waste in the city Salzgitter in the Metropolitan region Hannover-Braunschweig-Göttingen-Wolfsburg in southeas ...
* Schikorr reaction *
Waste Isolation Pilot Plant The Waste Isolation Pilot Plant, or WIPP, is the world's third deep geological repository (after Germany's Repository for radioactive waste Morsleben and the Schacht Asse II salt mine) licensed to store transuranic radioactive waste for 10,000 ...


References


External links


WDR Asse II Tour 3.7.2008
{{portal bar, Food Radioactive waste repositories Salt mines in Germany Wolfenbüttel (district) Economy of Lower Saxony