In the United States, concepts for underground disposal of radioactive waste in salt formations (in particular of high-level, heat-developing and persistent waste) were developed from the mid-fifties onwards. At the first Geneva Conference of the United Nations held in August 1955 to discuss the peaceful use of nuclear energy, the United States made many pieces of information on all fields of nuclear technology transparent within the framework of their programme "Atoms for Peace." During this Conference, an American geologist already concluded: Geologically, salt deposits seem to offer the least hazard for the disposal of High-level wastes." He justified this with the following characteristics of salt formations:
- The lack of groundwater movements
- the rich salt deposits allover the world
- the plasticity of salt.
The German geologists of the Federal Office for Ground Research in Hanover made use of the research results of their American colleagues and applied them to the Federal Republic of Germany.
The German Nuclear Committee was responsible for advising politicians and administrative bodies on questions concerning nuclear energy prior to the foundation of the Committee on Reactor Safety and Radiation Protection. This former organisation defined the future development of nuclear technology in Germany with the help of several "Atom Programmes". During the first German Atom Programme in 1957, the need for research activities into final disposal had already been pointed out.
In 1960, the Committee objected to the aboveground storage of radioactive waste in Germany because of the high population density, among others. In an expertise on the "Possibilities of disposing of radioactive waste underground" issued in 1963, the Federal Office for Ground Research concluded that the conditions of a "secular and safe storage" of radioactive waste would be "almost ideal" in Germany thanks to the existing salt formations. In order to proceed with this topic, the German Nuclear Committee decided on a solution mining of a cavern in a salt formation in order to be able to dispose of radioactive waste therein. Furthermore, it was decided to enter negotiations for the purchase of the salt mine Asse II which was still open at that time. After the Federal Office had certified that Asse would be suitable as a test repository for radioactive waste, the Federal Government purchased the salt mine and handed it over to the then Company for Radiation and Environmental Research (GSF) for further researching purposes. On April 4, 1967, a test programme for the disposal of low-level waste was started. In 1972, a programme for the disposal of medium-level waste followed.
In addition to the trial storage at Asse, the solution mining of a cavern in a Northern German salt dome was to be effected. This activity was part of a research project financed by the European Atomic Energy Community (EURATOM). The following factors were crucial in selecting a suitable site:
- the largest possible quantity of homogeneously formed rock salt was to be found
- the salt formation should have a thickness of at least 400 to 500 m so that a sufficient roof was to be formed above the cavern and a sufficient quantity of salt underneath
- the salt body should be large enough to make the solution mining of a cavern with a sufficient distance to the neighbouring rock possible
- the salt dome should not be situated too deep in the ground
- the overlying rock should be made of clay or marl in order to keep the technical efforts for required pipings as low as possible
- the salt dome should be situated near a river or sea to make the elimination of salt water arising during the solution mining of the cavern possible.
After several suitable salt domes had been found, the feasibility of the project was examined and discussed at two salt domes one after the other (Bunde in East Frisia and Oldenswort in Schleswig-Holstein). At both sites, however, local politicians had considerable doubts about the project. Eventually, a cavern was produced at Asse. The cavern at a depth of 900 to 1,000 metres was not produced by solution mining but by drifting. It was planned to mix granulated low- and medium-level waste to a suspension which was to be hardened in the cavern to form a monolithic block. The advantages of storing waste in a cavern against the storage of containers are the following: optimum use of the available hollow space, easy handling and lower costs. In addition to the research activities into the disposal at Asse, disposal projects at Gorleben and Konrad were started in the Federal Republic of Germany in the seventies. In the former GDR, the disposal project Morsleben was pursued.
The increased efforts can be traced back to extension of nuclear energy. Whereas only small quantities of nuclear waste had been produced during the fifites and sixties, larger quantities of waste and also irradiated fuel assemblies had to be expected due to the nuclear power plant projects of the seventies. Irradiated fuel assemblies were to be reprocessed. At the beginning of the seventies, the following idea took hold in the Federal Republic of Germany: A repository should be established at the reprocessing location in order to be able to store waste arising during reprocessing directly on site. In so doing, transport risks were to be minimised and the radioactivity was to be "concentrated" at a single location (zero-release concept).
