Critical groups for geological disposal performance assessments

International recommendations and many national regulations on deep geological disposal of radioactive waste include requirements to demonstrate that radiation doses and/or risks to individuals after waste disposal meet particular quantitative standards. Therefore, an important question for performance assessments (PAs) is how to define the characteristics of the relevant individuals so as to allow their radiation exposure to be assessed. In the USA and in the context of high-level waste (HLW) disposal, this question has been given an increased profile following the publication of the National Academy of Sciences (NAS) report on technical bases for Yucca Mountain standards. This paper presents a summary compilation and analysis of information on critical groups being prepared for the Electric Power Research Institute in order to inform judgements on assumptions for critical groups which might be used in PA of Yucca Mountain. Consideration has been given to the regulatory development of the concept of a critical group and its use in radiological assessments, including assessments of present day effluent releases as well as releases which might occur in the long term future as a result of land based disposal of solid radioactive waste