According to 10 CFR 60.2 (1) [Title 10 – Energy; Chapter I -- Nuclear Regulatory Commission; Part 60 -- Disposal of High-Level Radioactive Wastes in Geologic Repositories; Subpart A -- General Provisions], the term design basis events means:
(1)(i) Those natural and human-induced events that are reasonably likely to occur regularly, moderately frequently, or one or more times before permanent closure of the geologic repository operations area; and
(ii) Other natural and man-induced events that are considered unlikely, but sufficiently credible to warrant consideration, taking into account the potential for significant radiological impacts on public health and safety.
(2) The events described in paragraph (1)(i) of this definition are referred to as "Category 1" design basis events. The events described in paragraph (1)(ii) of this definition are referred to as "Category 2" design basis events.”