The concept of disposal of radioactive wastes in mined caverns in geological formations was proposed over two decades ago. During the formulative years of study, the research and development activities were directed primarily to the disposal of wastes in salt beds. During the latter half of the 1970–79 decade, the waste technology programs were expanded substantially in finances and personnel in the USA, canada, Sweden, and West Germany, and in consideration of a broader range of geologic media, including granite, basalt, tuff, and shale. This paper examines the state-of-the-art of the technology developed to date for geologic disposal and the key issues of concern to the public and technical communities, and provides an assessment of what is viewed as being required to transform the notion of geologic disposal from concept to fact. The position is taken that the level of technology is immediately adequate for the geologic disposal of low-level radioactive wastes, and for the retrievable storage of high-level wastes. Furthermore, it is the opinion of the authors that the technology programs planned for the 1980–89 decade will provide the resolution required for safe, permanent disposal of high-level wastes in mined geologic caverns.

INTRODUCTION
Historical Perspective.

In response to a request by the U.S. Atomic Energy Commission (AEC), the National Academy of Sciences--National Research Council (NAS-NRC) established a committee of geologists and geophysicists in 1955 for the purpose of considering the disposal of high-level radioactive wastes in geologic structures within the continental United states. In 1957, this committee proposed disposal of wastes in natural salt formations as the most promising method of the future (NAS-NRC Committee on Waste Disposal,' 1957). The recommendations of the committee resulted in the initiation of studies of high-level radioactive waste disposal in salt, with early investigations by the oak Ridge National Laboratory (ORNL) directed toward the disposal of liquid waste (Parker, and others, 1960). In 1961, the NAS-NRC Committee reviewed the progress of the work since 1955, and concluded that "… experience both in the field and in the laboratory on disposal of wastes in salt have been very productive, well conceived, and that plans for the future are very promising" (NAS-NRC Committee on Geologic Aspects of Radioactive Waste Disposal, 1961). Moreover, the Committee noted that" … the interpretations relating to disposal in salt are by the very nature of salt deposits capable of being extrapolated to a considerable degree from one deposit to another …" and recommended strongly that "the effect of storing dry packaged radioactive wastes in a salt deposit be tested …". As a consequence of these recommendations, Project Salt Vault was designed and conducted at the carey salt Mine near Lyons, Kansas in the 1960's, using irradiated fuel elements as a simulant for reprocessing calcined solidified wastes (Bradshaw and McClain, 1971). This study was followed by a conceptual repository design for the bedded salt lithology of the Lyons area, and the Subsequent abandonment of the site in 1972 for a variety of political and technical reasons.

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