NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competence and with regard for appropriate balance.

Support for this study was provided by the U.S. Department of Energy under cooperative agreement number DE-FG08-97NV12056. All opinions, findings, conclusions, and recommendations expressed herein are those of the authors and do not necessarily reflect the views of the U.S. Department of Energy.

Cover: The development of geologic repositories for the disposal of high-level radioactive waste presents technical and societal challenges. As is the case for other first-of-a-kind and complex projects, repository programs should proceed in stages, or steps, as recognized in waste disposal programs worldwide.