Repository 101: Multiple-barrier geological repository design and isolation strategies for safe disposal of radioactive materials

This introductory chapter provides basic insights and guiding principles for establishing and evaluating the long-term safe isolation of radioactive wastes in geological repositories. The intended audience is new technical researchers and reviewers, interested in understanding how their specific expertise is integrated into a multidiscipline safety assessment. The focus is on deep geological disposal, appropriate for the disposal of spent nuclear fuel (SNF), reprocessed high-level waste (HLW), and long-lived, intermediate level waste (LL/ILW). Many of the principles discussed here, however, equally apply to near-surface disposal of lower activity wastes. Two basic types of processes affecting the long-term safe containment and isolation of radioactive waste in deep geological repositories are examined: (1) delay-and-decay processes and (2) concentration-attenuation processes. The robustness of different types of isolation processes, based on their effectiveness and reliability, are discussed. A “top-down” safety assessment of an integrated, multiple-barrier repository system is vital to identify and prioritize safety-important barriers and processes and to use such safety importance insights to guide an efficient and effective research, development, and design program.