1 Introduction
Nuclear energy has been used for many years both in Germany and around the world. While Germany, in the wake of the accident at the Japanese nuclear power plant of Fukushima Daiichi (INES level 7, the highest in the International Nuclear and Radiological Events Scale) – the most serious rector accident since Chernobyl – took the decision to phase-out nuclear energy completely by the end of 2022, nuclear generating capacity is still being developed and expanded elsewhere around the globe.
The question of how to dispose of radioactive waste is one that is inextricably linked to nuclear energy usage. High-level radioactive heat-generating waste is produced from research and power reactors, this generally being in the form of spent fuel elements. There is also the low and intermediate-level, non-heat-generating waste that is obtained, e. g., from nuclear power plants, medical facilities and research activities.
Storage in deep geological formations has long been favoured internationally as the most sensible solution for the permanent disposal of high-level radioactive waste. Facilities already exist, or are being planned, for storing low and intermediate-level radioactive waste both in surface and in near-surface facilities and deep geological formations.
2 Nuclear energy usage in Germany and around the world
Fig. 1. Nuclear power plants in operation worldwide excl. West/Central Europe (1). // Bild 1. Kernkraftwerke in Betrieb/weltweit ohne West-/Zentraleuropa (1).
There are currently some 450 nuclear power stations operating in 31 countries with a total installed capacity of around 400,000 MW. Their global distribution is shown in Figures 1 and 2 (1). Germany’s seven nuclear power plants are all to be shut down by 2022.
A total of 52 nuclear power plants are now under construction worldwide – with a further 122 being planned. The five countries with the largest number of nuclear power plants are (1):
- USA 98 units
- France 58 units
- China 45 units
- Japan 39 units
- Russia 36 units
All nuclear-energy generating countries are currently planning to dispose of their high-level radioactive waste in deep geological repositories located within the territory of origin. While in the European Union (EU) the export of radioactive waste is essentially permitted provided certain specific conditions are met, Germany has nevertheless declared itself in favour of final disposal within its own territory and indeed this policy has now been enshrined in law. The search for and choice of suitable final disposal sites for high-level radioactive waste is now regulated by the Repository Site Selection Act (StandAG) (2, 3). Germany, like other countries around the world, is focusing on the host rock formations clay, salt and crystalline as likely host rocks (Figure 3).
Fig. 3. Sample images of clay, salt and crystalline rock (from left // to right). // Bild 3. Beispielbilder für Ton-, Salz- und Kristallingestein (von links nach rechts).
The following paper will initially present the repository projects currently under way in Germany before going on to review the international efforts being made in this area.
3 Final disposal projects in Germany
The final disposal projects now under way in Germany are reviewed elsewhere in this paper (see page 466 to 474) and so will only be briefly touched upon here.
3.1 Search for and choice of suitable sites for the final disposal of high-level radioactive heatgenerating waste
Germany does not at present possess a repository for high-level radioactive heat-generating waste, which essentially means spent fuel elements. This category of waste is currently held in interim storage at 16 different locations. The process of selecting a location as a potential disposal site was re-launched in 2017 and begins with what is referred-to as the “white geographical map” of Germany. Every region is analysed as to its particular suitability using a three-phase process based on a specific list of criteria. The objective is to identify the site that exhibits the “best possible safety level”, this involving broad public participation.
The international classification system is based on three categories of waste, namely LLW (low-level waste), ILW (intermediate-level waste) and HLW (high-level waste).
The German classification system uses the term “heat-generating waste”, which is roughly equivalent to HLW. This comprises waste materials with high activity concentrations and a high thermal output, due to the radioactive decay. A further distinction is made for waste with negligible heat generation (approximately equivalent to LLW and ILW). This category of waste exhibits low to medium levels of radioactivity and a low level of decay heat.
3.2 The Morsleben repository: closure of the facility for low and intermediate-level radioactive waste
The Morsleben Repository for Radioactive Waste (ERAM) was constructed at the former Bartensleben salt and potash mine, which lies on the border between the federal states of Saxony-Anhalt and Lower Saxony. The Morsleben repository was operated by the former GDR as a final disposal site for low and intermediate-level radioactive waste. Radioactive waste was stored there up until 1998. The facility is currently being prepared for closure.
ERAM is therefore the first storage site for radioactive waste in Germany to be safely closed in line with a nuclear-sector planning approval procedure. This operation includes the installation of sealing structures designed to act as geotechnical barriers in underground repositories. Figure 4 depicts an experimental (in situ) barrier seal of this kind some 25 m in length.
Fig. 4. In situ structural seal at the Morsleben repository (4). // Bild 4. In-Situ-Abdichtbauwerk im Endlager Morsleben (4).
3.3 Asse II mine: retrieval of low and intermediate-level radioactive waste
Up until 1978 low and intermediate-level radioactive waste was stored in certain parts of the Asse II former salt mine at Wolfenbüttel in Lower Saxony. The photo in Figure 5, taken in 1975, shows “lost shielding containers” being placed in a storage chamber. Here the waste is being placed in permanent storage along with the “lost” concrete shielding.
Fig. 5. Storage of “lost shielding containers” in 1975 (4). // Bild 5. Einlagerung von VBA-Behältern im Jahr 1975 (4).
Following a leach inflow observed in 1998, along with cases of instability identified in some parts of the mine workings, it was decided that the stored waste should be retrieved from the underground repository. The “Act to Accelerate the Retrieval of Radio-active Waste and the Decommissioning of the Asse II mine”(the Lex Asse) subsequently came into force in April 2013.
3.4 Konrad mine: construction and subsequent operation of a repository for low and intermediate-level radioactive waste
Konrad mine, which is a disused iron-ore mine near Salzgitter, is currently being converted for use as a repository for radioactive waste with negligible heat generation (low and intermediate-level radioactive waste). Around 90 % of Germany’s radioactive waste is to be stored at the Konrad disposal facility. This quantity of material contains about 1 % of the radioactivity of all the radioactive waste produced in Germany. The disposal operation is due to commence in 2027. Figure 6 gives an idea of the kind of preparations now being made below ground. This photo shows a material transport tunnel leading from Konrad 2 shaft to the storage chambers.
Fig. 6. Material transport tunnel leading from Konrad 2 shaft to the storage chambers (4). // Bild 6. Einlagerungstransportstrecke von Schacht Konrad 2 zu den Einlagerungskammern (4).
4 Countries with final disposal projects for high-level radioactive waste
In order to undertake an international comparison of the repository projects currently under way we have first carried out a review of all the countries that operate nuclear power plants, have operated nuclear power plants or intend to operate them at some time in the future. A search was then undertaken to determine whether specific final disposal projects or plans exist in the 38 countries in question. The countries involved can be broken down roughly into five groups:
- countries with a specified final disposal site;
- countries with definite long-term final disposal projects;
- countries with unspecified long-term final disposal projects;
- countries with a multinational approach; and
- countries with no discernible waste storage plans.
These five groups represent the author’s attempt to provide a better summary oversight of the individual country data obtained from the study. The groupings are based on the collected data and search results.
A survey of the host rock formations that have been selected or are under consideration in the respective countries shows that 17 countries have opted for, or are considering, crystalline rock (usually metamorphic rock or unmetamorphosed plutonite), nine are in favour of clay rock (clastic sedimentary rock) and three favour salt rock (chemical sedimentary rock). The USA also has a repository project based on volcanic tuff as the host formation (this project is currently on standby, see Table 1). 17 of the countries in question either have still not decided on the nature of the host rock, have no repository project or plans under way or were in no position to provide reliable information for the study.
It is important to note that the global distribution of preferred host rock formations does not allow definitive conclusions to be drawn as to their potential suitability as locations for the siting of repositories. However, this breakdown does reflect the geological situation as it exists in the different countries. The host rocks selected for the task exhibit different characteristics that can be used to derive specific requirements for the design of the containers and underground storage facilities.
All the acquired data on the countries in question is compiled in Table 1.
Table 1. Countries with final disposal projects for high-level radioactive waste and/or nuclear power plants (1, 8, 9, 10). // Tabelle 1. Länder mit Endlagerprojekten für hochradioaktive Abfälle und/oder Kernkraftwerken (1, 8, 9, 10).
4.1 Countries with identified repository sites
Finland, France and Sweden lead the field when it comes to repository projects with identified storage sites, rock laboratories and significant progress in the construction phase (see Table 1).
Finland and Sweden have opted for crystalline as the host rock, while France has chosen clay rock. Disposal operations with the first batch of containers is due to commence in the course of the next ten years. Finland is expected to begin this work in the early 2020s, to be followed by France with a projected storage start-date in 2025. Sweden is planning to begin its disposal operation in 2030. Finland’s final disposal project at its Olkiluoto facility is briefly described below.
A permanent storage facility for high-level radioactive waste is designed to prevent any prohibited release of radionuclides. This aim is achieved by installing a multi-barrier system capable of containing the waste material. This system is composed of technical, geotechnical and geological barriers.
Fig. 7. The multi-barrier concept (5). // Bild 7. Multibarrierenkonzept (5).
As Figure 7 shows, the fuel pellet is encased within a fuel rod. Several such rods are combined to create the fuel assembly. After having served their use spent fuel elements are first stored underwater in wet tanks at the nuclear power plant. They are then put into wet or dry intermediate storage before being transferred to a final disposal facility. In the Finnish and Swedish concept these containers are also enclosed within a copper “overpack”. The latter is both gas-tight and corrosion-resistant (Figures 7 middle and 8). The storage container protects the fuel elements from mechanical stress.
Fig. 8. Container for spent fuel elements (5). // Bild 8. Behälter für abgebrannte Brennelemente (5).
Figure 8 shows a typical container designed to hold twelve spent fuel elements. At the Olkiluoto facility all the storage containers are to be installed vertically in the host rock at depths of between 400 and 450 m (Figures 9 and 10). The copper-enclosed container represents the technical barrier within the multi-barrier system.
Fig. 9. Storage and backfill arrangement (5). // Bild 9. Einlagerungs- und Versatzschema (5).
All the excavated cavities are completely filled in. In the area of the container itself this is done using bentonite blocks (Figure 9, no. 2), while the access tunnels are also filled with clay or bentonite buffer blocks and additionally with bentonite pellets (Figure 9, no. 3). Once the disposal operation has been completed and the containers are in place all the connecting tunnels and shafts are backfilled with bentonite. This prevents any flow paths developing for water and leaches and also helps maintain the stability of the mine infrastructure. The bentonite buffer, backfill and sealing structures combine to create the geotechnical barriers required for the final disposal site.
Bentonite is a clay whose volume expands fourfold when in contact with water, yet which allows almost no water to pass through. As it swells the bentonite fills up the cavity space between the host rock and the storage containers. This prevents water getting to the canisters. In the event of a leakage at one of the containers there is no possibility of radionuclides being transferred into the host rock or into the biosphere.
The bedrock in the Olkiluoto area (gneiss) is somewhere between 1,800 and 1,900 million years old (Figure 9, no. 4). This rock should protect the containers from external elements and also creates mechanically and chemically stable conditions for the repository in general. The host rock forms the geological barrier within the multi-barrier concept.
Figure 10 shows the underground layout of the repository. Access is provided by several surface shafts and a spiral tunnel. The diagram shows the general infrastructure along with the location of the waste storage area where the containers are to be kept.
Fig. 10. Underground layout and location of the waste storage area (5). // Bild 10. Grubengebäude und Lage des Einlagerungsbereichs (5).
4.2 Countries with definite long-term final disposal projects
This group comprises 13 countries that have real intentions of organising final disposal facilities in deep geological formations. Here too clay, salt and crystalline rocks are being considered as the potential host environment. Geological data are being collected for the site decision-making process, though in varying degrees of detail.
In some of the countries, such as Switzerland, the site selection process is already well advanced and a location is expected to be chosen within a few years. The plan is to commence the disposal process in 2060. Germany has still a long way to go before the decision is made on a suitable disposal site. The aim is to reach a decision by 2031. We are therefore lagging one or two decades behind Switzerland in terms of the site selection process.
Switzerland and Germany now find themselves in a procedure in which the public has been, or will be, heavily involved. In the other countries that feature in this group it is likely that the storage site will be selected by the national government without any significant participation formats. Here it is anticipated that the site decision-making processes and the construction of the repository will generally be completed at a faster pace. In Russia, e. g., the site is expected to be chosen by 2025 and the waste disposal operation is likely to commence by the year 2035.
Countries that have definite long-term waste disposal projects can be listed as: Belgium, Bulgaria, China, Germany, the UK, India, Japan, Canada, Russia, Switzerland, the Czech Republic, Hungary and the USA (see Table 1).
4.3 Countries with unspecified long-term final disposal projects
The countries listed below are giving initial considerations to the development of a final disposal project. Some have carried out design studies for a site selection process and have engaged in exploration programmes. In some individual cases potential dates have been named for the possible commencement of disposal operations. However none of these activities could yet be qualified as “planning in-depth”. This group comprises: Argentina, Brazil, Lithuania, Mexico, Romania, Slovenia, Slovakia, Spain, Taiwan, Ukraine (see Table 1).
4.4 Countries with a multinational approach
The idea of adopting a multinational approach to final disposal projects dates back to the 1970s. There are several considerations that may lie behind this thinking, including:
- lack of resources for establishing an independent geological final disposal facility;
- insufficient technical know-how for constructing a geological final disposal facility;
- international cooperation offers economic benefits;
- international cooperation has ecological advantages.
Adopting a multinational approach to repository projects with a view to finding common solutions is also an acceptable policy within the EU, though this does require a legally binding international agreement between the partner countries involved. Moreover, such an arrangement raises a number of questions with regard to:
- safeguards (monitoring the nuclear material);
- governance (control and regulation systems);
- national and international (public) acceptance;
- cross-border transport; and
- national and international law.
According to research, the countries that have been identified as considering a multinational approach comprise Latvia, Slovenia, Slovakia and the United Arab Emirates.
However, there are still no tangible signs that the nations in question are engaged in specific studies or are making visible efforts in this area.
4.5 Countries with no discernible final disposal plans
The following countries either currently have, or in future will have, high-level radioactive waste from nuclear power plant operations: Egypt, Armenia, Iran, Italy, Kazakhstan, the Netherlands, Pakistan, South Africa, Turkey, Uzbekistan, the United Arab Emirates and Belarus. However, these countries either have no discernible final disposal projects or plans or were not open to survey.
4.6 Final disposal in deep boreholes
As shown in the table 1, the possibility of storing radioactive waste in deep boreholes is also being examined in some individual cases. Germany too has explored the potential of this particular option (see page 475 to 484). The example given in Figure 11 shows the basic features of such a storage system (6).
Fig. 11. Schematic example of borehole disposal (6). // Bild 11. Mögliches Schema für eine Bohrlochlagerung (6).
While this particular option is being given further consideration in the USA, e. g., and is currently the subject of active research and development activities, Germany has now decided – following a recommendation from the Commission for the Storage of High-level Radioactive Waste – that it will no longer actively pursue this particular disposal route (7).
5 Summary
If we look beyond the borders of Germany it is clear that nuclear energy will continue to play a major role in electricity generation for years to come. But Germany has opted for a different pathway and after 2022 nuclear power will no longer feature as part of the national energy mix. What remains is the challenge of disposing of and storing the radioactive waste. The search for a suitable site for the final disposal of high-level radioactive waste has been regulated by the Repository Site Selection Act that came into force in 2017 (3). Clay, crystalline and salt rock formations have all been investigated as potential host rocks. This selection process, and the work of constructing the repository itself, is likely to last for many decades to come.
On an international level the progress achieved and the efforts being made in the development of repositories for the disposal of radioactive waste can be broken down as follows: three countries have identified final disposal sites (Finland, France and Sweden), 13 countries have definite long-term final disposal projects and ten countries have long-term, though unspecified, final disposal plans. There are also twelve countries that are using, have used or would like to use nuclear energy, but as yet have no discernible plans for dealing with the resulting radioactive waste.
As a conclusion it can be said that the storage of highly radioactive waste in final disposals is well underway at international level. In the decades to come further final disposal projects will follow. In Germany, the Repository Site Selection Act provides for a decision-taking route to a repository. We are, however, only at the beginning of a long process.
References
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