A deep geological repository is a way of storing hazardous or radioactive waste within a stable geologic environment, typically 200–1,000 m underground. It entails a combination of waste form, waste package, engineered seals and geology that is suited to provide a high level of long-term isolation and containment without future maintenance. This is intended to prevent harm to human health or the environment from the radiological hazards of the waste. A number of mercury, cyanide and arsenic waste repositories are operating worldwide including Canada (Giant Mine) and Germany (potash mines in Herfa-Neurode and Zielitz). Radioactive waste storage sites are under construction with the Onkalo in Finland being the most advanced.
Principles and background Highly toxic waste that cannot be further recycled must be stored in isolation, to avoid contamination of air, ground and underground water. Deep geological repository is a type of long-term storage that isolates waste in geological structures that are expected to be stable for millions of years, with a number of natural and engineered barriers. Natural barriers include water-impermeable (e.g. clay) and gas-impermeable (e.g. salt) layers of rock above and surrounding the underground storage. Engineered barriers include bentonite clay and cement.
In 2011, the International Panel on Fissile Materials said: It is widely accepted that spent nuclear fuel and high-level reprocessing and plutonium wastes require well-designed storage for periods ranging from tens of thousands to a million years, to minimize releases of the contained radioactivity into the environment. Safeguards are also required to ensure that neither plutonium nor highly enriched uranium is diverted to weapon use. There is general agreement that placing spent nuclear fuel in repositories hundreds of meters below the surface would be safer than indefinite storage of spent fuel on the surface [of the earth].
Common elements of repositories include the radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area.
A storage space hundreds of metres below the ground needs to withstand the effects of one or more future glaciations, with thick ice sheets resting on top of the rock. The presence of ice sheets affects the hydrostatic pressure at repository depth, groundwater flow and chemistry, and the potential for earthquakes. This is being taken into consideration by organizations preparing for long-term waste repositories in Sweden, Finland, Canada and some other countries that have to assess the effects of future glaciations.
Despite a long-standing agreement among many experts that geological disposal can be safe, technologically feasible and environmentally sound, a large part of the general public in many countries remains skeptical as a result of anti-nuclear campaigns.Vandenbosch, Robert, and Susanne E. Vandenbosch. 2007. Nuclear waste stalemate. Salt Lake City, Utah: University of Utah Press. One of the challenges facing the supporters of these efforts is to demonstrate confidently that a repository will contain wastes for so long that any releases that might take place in the future will pose no significant health or environmental risk.
Nuclear reprocessing does not eliminate the need for a repository, but reduces the volume, the long-term radiation hazard, and long-term heat dissipation capacity needed. Reprocessing does not eliminate the political and community challenges to repository siting.
Natural radioactive repositories Natural uranium ore deposits serve as proof of concept for stability of radioactive elements in geological formations—Cigar Lake Mine for example is a natural deposit of highly concentrated uranium ore located under sandstone and a quartz layer at a depth of 450 m, that is 1 billion years old with no radioactive leaks to the surface.
The ability of natural geologic barriers to isolate radioactive waste is demonstrated by the natural nuclear fission reactors at Oklo, Gabon. During their long reaction period about 5.4 tonnes of fission products as well as 1.5 tonnes of plutonium together with other transuranic elements were generated in the uranium ore body. This plutonium and the other transuranics remained immobile until the present day, a span of almost 2 billion years.R. Naudet. 1976. The Oklos nuclear reactors: 1800 millions years ago. Interdisciplinary Science Reviews, 1(1) pp. 72–84. This is remarkable as ground water had ready access to the deposits and they were not in a chemically inert form, such as glass.
Research Deep geologic disposal has been studied for several decades, including laboratory tests, exploratory boreholes, and the construction and operation of underground research laboratories where large-scale in-situ tests are being conducted. Major underground test facilities are listed below.
Country Facility name Location Geology Depth Status Belgium HADES Underground Research Facility Mol plastic clay 223 m in operation 1982 Canada AECL Underground Research Laboratory Pinawa granite 420 m 1990–2006 Finland Onkalo Olkiluoto granite 400 m under construction France Meuse/Haute Marne Underground Research Laboratory Bure claystone 500 m in operation 1999 Japan Horonobe Underground Research Lab Horonobe sedimentary rock 500 m under construction Japan Mizunami Underground Research Lab Mizunami granite 1000 m under construction South Korea KAERI Underground Research Tunnel Deajeon granite 120 m in operation 2006 Sweden Äspö Hard Rock Laboratory Oskarshamn granite 450 m in operation 1995 Switzerland Grimsel Test Site Grimsel Pass granite 450 m in operation 1984 Switzerland Mont Terri Rock Laboratory Mont Terri claystone 300 m in operation 1996 United States Yucca Mountain nuclear waste repository Nevada tuff, ignimbrite 50 m 1997–2008
Nuclear repository sites
Country Facility Name Location Waste Geology Depth Status Argentina Sierra del Medio Gastre granite Proposed 1976, stopped 1996 Belgium Hades (High-activity disposal experimental site) high-level waste plastic clay ~225 m under discussion Canada OPG DGR Ontario 200,000 m3 L&ILW argillaceous limestone 680 m license application 2011, canceled 2020 Canada NWMO DGR Ontario spent fuel siting China under discussion Finland VLJ Olkiluoto L&ILW tonalite 60–100 m in operation 1992T. Aikas and P. Antilla. 2008. Repositories for low- and intermediate-level waste in Finland. Reviews in Eng. Geology 19, pp. 67–71. Finland Loviisa L&ILW granite 120 m in operation 1998 Finland Onkalo Olkiluoto spent fuel granite 400 m under construction France Cigéo (Centre Industriel de Stockage Géologique) Bure, Meuse high-level waste mudstone 500 m license application 2023 Germany Schacht Asse II Lower Saxony salt dome 750 m closed 1995 Germany Morsleben Saxony-Anhalt 40,000 m3 L&ILW salt dome 630 m closed 1998 Germany Gorleben Lower Saxony high-level waste salt dome proposed, on hold Germany Schacht Konrad Lower Saxony 303,000 m3 L&ILW sedimentary rock 800 m under construction Japan Vitrified high-level waste >300 m under discussion South Korea Wolseong Gyeongju L&ILW 80 m in operation 2015 South Korea high-level waste
siting Sweden SFR Forsmark 63,000 m3 L&ILW granite 50 m in operation 1988 (archived) Sweden
Forsmark spent fuel granite 450 m license application 2011 License application March 2011 Switzerland high-level waste clay siting United Kingdom high-level waste under discussion United States Waste Isolation Pilot Plant New Mexico transuranic waste salt bed 655 m in operation 1999 United States Yucca Mountain Project Nevada 70,000 ton HLW ignimbrite 200–300 m proposed, canceled 2010
Status of repository at certain sites
The process of selecting appropriate deep final repositories is under way in several countries, with the first expected to be commissioned some time after 2010.
Australia There was a proposal in the early 2000s for an international high level waste repository in Australia and Russia.Disposition of high-level waste and spent nuclear fuel: The continuing societal and technical challenges. Washington, DC: National Academy Press. 2001. Since the proposal for a global repository in Australia, which has never produced nuclear power, and has one research reactor, was raised, domestic political objections have been loud and sustained, making such a facility in Australia unlikely.
Canada
Giant Mine has been used as a deep repository for storage of highly toxic arsenic waste in the form of powder. As of 2020 there is ongoing research to reprocess the waste into a frozen block form which is more chemically stable and prevents water contamination.
On Nov 28, 2024, the NWMO selected the Wabigoon Lake Ojibway Nation-Ignace area as the site for Canada's deep geological repository for used nuclear fuel.
Finland The Onkalo site in Finland based on the KBS-3 technology, is the furthest along the road to becoming operational among repositories worldwide. Posiva started construction of the site in 2004. The Finnish government issued the company a licence for constructing the final disposal facility in November 2015. Posiva has applied for an operating licence to begin disposals, but , the response from the regulator, STUK, is delayed until the end of June 2026.
Germany A number of repositories including potash mines in Herfa-Neurode and Zielitz have been used for years for the storage of highly toxic mercury, cyanide and arsenic waste. There is little debate in Germany regarding toxic waste, in spite of the fact that unlike nuclear waste, it does not lose toxicity with time.
There is a debate about the search for a final repository for radioactive waste, accompanied by protests, especially in the Gorleben village in the Wendland area, which was seen as ideal for the final repository until 1990 because of its location in a remote, economically depressed corner of West Germany, next to the closed border to the former East Germany. After reunification, the village is now close to the center of Germany, and is now used for temporary storage of nuclear waste.
The pit Asse II is a former salt mine in the mountain range of Asse in Lower Saxony/Germany, that was allegedly used as a research mine since 1965. Between 1967 and 1978, radioactive waste was placed in storage. Research indicated that brine contaminated with radioactive caesium-137, plutonium and strontium was leaking from the mine since 1988 but was not reported until June 2008. The repository for radioactive waste Morsleben is a deep geological repository for radioactive waste in the rock salt mine Bartensleben in Morsleben, in Saxony-Anhalt/Germany, that was used from 1972 to 1998. Since 2003, of salt-concrete has been pumped into the pit to temporarily stabilize the upper levels.
Sweden Approval was granted in January 2022 for the construction of a direct disposal facility using KBS-3 technology, on the site of the Forsmark nuclear power plant.
United Kingdom The UK Government, in common with many other countries and supported by scientific advice, has identified permanent deep underground disposal as the most appropriate means of disposing of higher activity radioactive waste.
Radioactive Waste Management (RWM) was established in 2014 to deliver a Geological Disposal Facility (GDF) and is a subsidiary of the Nuclear Decommissioning Authority (NDA) which is responsible for clean-up of the UK's historical nuclear sites. In 2022, Nuclear Waste Services (NWS) formed from the merger of RWM with the Low Level Waste Repository in Cumbria.