Nuclear waste in Germany

The complex search for a repository

The so-called "hot" nuclear waste accumulates in nuclear power plants in the form of the spent fuel elements; in the case of large pressurized water reactors still in operation in Germany, this involves around 30 metric tons of material per year from the reactor core; it contains around 95 percent of the radioactivity to be disposed of. The spent fuel elements must be stored in a decay pool for several years before the activity of the shorter-lived fission products has dropped to the point where constant water cooling is no longer required and removal is possible. Plutonium (Pu) is a toxic and radioactive heavy metal; it is found in nature only in minute traces in very old rocks. During the operation of nuclear reactors, large amounts of fissile Pu₂₃₉ are formed from uranium₂₃₈ in the fuel assemblies, a low-volatility nuclide that is released from the fuel or from a package, e.g., with other radioactive fission products, only at very high temperatures. In water, Pu₂₃₉, like all other nuclides, is soluble; it is used after reprocessing as fissile material in fresh "MOX" fuel assemblies, but also in nuclear weapons. The half-life of Pu₂₃₉, which is the time period in which the radiation has decayed to half of its original value, is about 24,000 years; to a quarter the initial radiation has reduced after 2 half-life periods, i.e. after 48000 years, and so on. The activity never becomes zero; it reduces after x-half-lives to a value that is probably still measurable, but insignificant when measured against the radiation level on the earth's surface. The waste must be prepared for final disposal, in technical language "conditioned". The mixture with the predominantly non-fissile isotopes is vitrified and taken to an interim storage facility, where it must continue to decay for several decades before the heat generation has decreased to the point where final disposal is possible.

As a reminder

The "hot" topic is of concern to power plant operators, the scientific community and politicians; planning for possible steps to realize final waste disposal began as early as the German government's second nuclear program (1963 to 1967). Thus, especially in the nuclear research centers, working groups were established to deal with the scientific fundamentals of final disposal and its experimental validation. In Wackersdorf, Bavaria, construction of a reprocessing plant for spent fuel elements to obtain fissile uranium/plutonium as fuel for new nuclear power plants was started in 1985. Construction activity was halted four years later. Opposition from opponents of reprocessing was so great that construction in Germany was banned "for all time." Based on this decision, it was clear that the nuclear waste, which is particularly contaminated due to the heat generated in the course of the radioactive decay of long-lived fission products, must be disposed of in Germany for all time.

Requirements for a final repository for highly radioactive waste

The basis for the search for a final repository for highly radioactive waste is a long-term storage safety of one million years. The nuclear waste should be retrievable for 500 years. The search is being conducted at depths of between 300 and 1,500 meters, where, among other things, seismic conditions, fault potential in the overburden or the insulating capacity of the rock are right. The newly founded Federal Company for Final Disposal (BGE) has officially begun the search for a site; the search for a nuclear waste repository is to be open-ended, transparent and strictly scientific. No region is to be excluded from the outset. However, with the help of existing data, the experts first sort out regions that are out of the question - for example, because there is a risk of earthquakes or because many people live there. Theoretically suitable sites are then determined on the basis of other criteria. This is followed by exploration above and then below ground. A site is to be found by 2031. Only certain host rocks are suitable for storing the waste. Specifically, salt, clay and crystalline formations are being investigated. The granite deposits in central Germany also belong to the latter. This rock is easily permeable to water, which is why the waste would have to be secured with additional barriers. Experts judge clay or salt rock to be more suitable, of which Saxony-Anhalt has the most potential sites among the central German states.

Pilot tests, facilities and findings

The Asse salt mine in Lower Saxony was supposed to store nuclear waste for eternity. However, Asse II turned out to be a debacle. After just 40 years of operation, eternity is over. From 1967 to 1978, about 126,000 barrels with lightly and moderately radioactively contaminated material were stored - for research purposes. In fact, however, the nuclear power plant operators used the Asse to dispose of their "normal" radioactive waste there at low cost. Since 1978, around twelve cubic meters of water have been seeping in every day at a depth of over 600 meters; without consequences, almost unnoticed for over 30 years. Only when this became known to a wider public in 2009 was action taken. In 2008, the German government replaced the Helmholtz Center as operator of the Asse with the Federal Office for Radiation Protection (BfS). Since then, the Asse has been under nuclear law and under the supervision of the Federal Ministry for the Environment. New expert reports made the unsuitability of the Asse as a repository increasingly clear. At the beginning of 2011, the BfS pleaded for the nuclear waste to be taken out of the Asse again. According to the current state of knowledge, this was the best option for the further handling of the radioactive waste stored there. The cost of the retrieval operation is estimated at around four to six billion euros, and the duration, according to current estimates by the BfS, is around ten years. The Gorleben salt dome was examined from 1979 to 2000 to determine its suitability as a final repository for all types of radioactive waste. The site was determined not only on the basis of its geology, but primarily for political and regional economic considerations. The exploration of the salt dome was interrupted in 2000 at the instigation of the German government. The following years were to be used to clarify conceptual and safety-related issues regarding final disposal. The moratorium ended in March 2010. At the end of 2010, the State Office for Mining, Energy and Geology ordered immediate enforcement to resume exploration work. The planned final storage of nuclear waste in the Gorleben salt dome and the associated Castor transports are regularly the cause of fierce protests, demonstrations and blockade actions by tens of thousands of opponents of nuclear power. Nevertheless, Gorleben is not out of the running in the search for a final repository. The Konrad shaft in a former iron ore mine near Salzgitter has been under discussion as a final repository for low- or intermediate-level waste for decades. In 2006, the Konrad shaft was opened for use. Preparations for the development of the shaft as a final repository are progressing. The BfS expects that the first radioactive waste can be stored in 2022. The Morsleben salt dome in Saxony-Anhalt was put into operation as a repository by the GDR in the early 1970s. It was considered to be at high risk of collapse and could only be secured at great expense. Between 1970 and 2000, a large volume (37,000 m³) of so-called low- and intermediate-level waste from East German nuclear power plants, as well as from research and medicine, was emplaced - a controversial procedure because groundwater has been shown to seep into the storage tunnels. In 2001, the BfS decided to refrain from further storage in Morsleben. Currently, attempts are being made to seal the chambers with the nuclear waste. Backfilling of the chambers is not to begin until the relevant permits have been issued. After that, this waste would no longer be retrievable. Morsleben is not being considered as a nationwide final repository in the search that has now begun. In 2017, none of the 30 countries that use nuclear energy had a suitable final repository for high-level nuclear waste; corresponding planning and preparatory work has been underway in many countries for about four decades. To date, high-level waste has been reprocessed or stored directly in interim storage.

500-year retrievable

In Germany, a total of about 600,000 m³of nuclear waste is awaiting final disposal, including slightly more than half from the decommissioning of nuclear power plants (NPPs). According to the report of the Repository Commission, the final disposal of high-level radioactive waste in Germany will drag on well into the 22nd century. The commission expects storage to end between the years 2075 and 2130, and the stored waste should be "retrievable" for 500 years, as mentioned above, in case there are problems. A sealed repository mine is expected between 2095 and 2170 or even later. Accordingly, highly radioactive waste would have to be housed in interim storage facilities until after 2100. Final storage costs of about 50 to 170 billion euros are predicted. Final storage is officially a matter for the state and no longer the responsibility of the power plant operators. As already mentioned, a final repository is to be found by 2031 and then expanded. This would significantly exceed the original deadlines for interim storage and castors, which are designed for 40 years.