NRC position on optimization for a potential geologic repository

Brittain E. Hill (US NRC) gave a presentation on the 'NRC position on Optimisation for a Potential Geologic Repository'. Regulations governing the potential repository at Yucca Mountain are contained in 10 CFR Part 63, which covers both the pre-closure, operational period and the period of time following closure of the repository. B. Hill explained that following a public comment period on the proposed revisions, NRC is currently updating its regulations to be consistent with the revised EPA standards for the 10 000 yr to 1 000 000 yr post-closure period. One of the requirements in Part 63 for the pre-closure, operational period is to reduce radiation exposures to As Low As Reasonably Achievable during the operational phase of the potential repository. Detailed radiation protection criteria are provided as well. For the period following permanent closure of the repository, NRC has numerous regulatory requirements to protect public health and safety, the environment, and the defence and security needs of the collective people of the United States. These requirements, which are presented in the accompanying paper, represent an optimised approach that ensures that regulations are appropriately protective and provide a transparent basis to judge the safety of the proposed repository far into the future. They include demonstration of the understanding of the capability of barrier performance, a total-system performance assessment which must be used to demonstrate compliance with safety standards. Confidence that the geologic repository is optimised to protect public health and safety and the environment also is achieved through a performance confirmation programme and repository oversight must continue following permanent closure. NRC considers that compliance with these requirements is sufficient, and appropriately optimised, to ensure public health and safety. The ALARA principle, while appropriate for pre-closure an d decommissioning operations, does not apply to post-closure. If the repository system is shown to be safe, further design modifications incur additional costs with values that are difficult to judge against speculative changes in future societies and economies. As an additional consideration, deep geologic disposal, by its very nature, already is viewed as ALARA. There are few technological alternatives in repository design (10 CFR Part 63). Thus, NRC concludes that its post-closure regulatory requirements represent a sufficiently optimised approach to protecting the public. In summary, safety of the potential geologic repository at Yucca Mountain will be evaluated by considerably more than compliance with a numerical dose standard