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.

Compressed Air Energy storage (CAES) in underground caverns and Underground Pumped Hydro Storage (UPHS) are systems which can be used for electrical power generation during peak demand periods. Key features for economical use of such systems involve the structural and leakage stabilities of the storage caverns over operational lifetimes of some 30 years. A goal of this paper is to establish a consistent set of stability and design criteria for caverns in hard rock, which are both practical to the designer and applicable to numerical modeling and failure probability assessment techniques. To formulate stability criteria, the phenomenological modes of potential instability are identified for the physical situations and "quantified" in terms of appropriate constitutive laws of material behavior. INTRODUCTION Compressed Air Energy storage (CAES) in underground caverns and Underground Pumped Hydro Storage (UPHS) are two methods for storing energy that can be used for generation of electrical power during peak demand period. In the CAES concept, air is compressed and stored in underground caverns during off-peak demand periods, and withdrawn and used with surface turbine systems to generate electrical power during peak demand periods. In the UPHS concept, water is pumped from underground caverns to an upper reservoir during off-peak demand periods. During periods of peak demand, electrical energy is produced when the water in the. surface reservoir is permitted to flow down a penstock shaft, through a water-power turbine system, and into an underground reservoir. For these systems to be economical, the structural and leakage stabilities of the storage caverns must be maintained over an operational lifetime of some 30 years. The objectives of this paper are to examine stability and design criteria for CAES and UPHS caverns in hard rock in terms of performance criteria and acceptability limits, and to present some numerical modeling results which illustrate the mechanical and thermal responses of the caverns during construction and operation. SYSTEM CHARACTERISTICS The underground layout of a compensated CAES system in hardrock consists of a collection of parallel storage caverns, each of which is connected at either end by inclined entry's to common (air and water) crosscut tunnels. The crosscut (air) tunnels are connected to the surface compression/generation equipment by an air shaft and to a surface water reservoir by a water inlet/outlet shaft. Water from the surface reservoir provides a compensating head for maintenance of constant air pressure (with varying volume) in the storage caverns. This is designated a "wet" system because of the rise and fall of water in the caverns during the withdrawal (generation cycle) and injection (compression cycle) of compressed air. To prevent air ejection through the water shaft, the base of the shaft and any intermediate water storage caverns must be situated at greater depth than that of the air storage caverns. Because of turbine machinery limitations and pressure losses during the generation cycle, a maximum air pressure of about 7 to 7.5 MPa is required, dictating a facility depth of 715 to 765 m.