Reference concepts for geologic disposal of used nuclear fuel and high-level radioactive waste in
the U.S. are developed, including geologic settings and engineered barriers. Repository thermal
analysis is demonstrated for a range of waste types from projected future, advanced nuclear fuel
cycles. The results show significant differences among geologic media considered (clay/shale,
crystalline rock, salt), and also that waste package size and waste loading must be limited to meet
targeted maximum temperature values.

U.S. efforts to site and construct a deep geologic repository for used fuel and high level radioactive waste (HLW) proceeded in fits and starts over a three decade period from the late 1950s until 1982, when the U.S. Congress enacted the Nuclear Waste Policy Act (NWPA). This legislation codified a national approach for developing a deep geologic repository. Amendment of the NWPA in 1987 resulted in a number of dramatic changes in direction for the U.S. program, most notably the selection of Yucca Mountain as the only site of the three remaining candidates for continued investigation.