GEOLOGIC MAPPING IN THE REGULATORY REVIEW PROCESS FOR NEW NUCLEAR POWER FACILITIES AT THE U.S. NUCLEAR REGULATORY COMMISSION (NRC)

Regulatory requirements in the Code of Federal Regulations, specifically 10 CFR 100.23, support the concept of geologic mapping of safety-related excavations at sites for proposed new nuclear power facilities to evaluate site suitability and adequacy of design bases with due consideration for geologic and seismic characteristics of the site. 10 CFR 100.23(c) specifies the need for geologic data on tectonic and non-tectonic surface deformation, earthquake recurrence rates, and fault geometry and slip rates. 10 CFR 100.23(d) explictly states that geologic and seismic siting factors related to design must include determination of the potential for tectonic and non-tectonic surface deformation. Guidance in NRC Regulatory Guide 1.132 indicates that excavations for safety-related structures, and other excavations important for verifying subsurface conditions at the site, should be mapped in detail by geologists. NRC Regulatory Guide 1.208 states that faults exposed in site excavations should be mapped and assessed in regard to rupture potential while walls and floors of the excavations are exposed, to include assessment of non-tectonic surface and near-surface deformation.

As part of the regulatory review process at the NRC, an applicant conducts geologic mapping of excavations for safety-related structures at and adjacent to the nuclear island, and NRC geologists review the resulting geologic maps and associated data and directly examine the mapped foundation rock units and geologic features in the field to confirm that no potentially detrimental tectonic or non-tectonic features occur in the excavations. NRC geologists specifically evaluate geometry and field relationships of tectonic features, including data on relative ages of these features and constraining ages established from mineralogy and radiometric age dates acquired by the applicant; relationships of site tectonic structures to regional tectonic features; and lithologies, including susceptibility to dissolution. These activities, which are implemented at each proposed new reactor site, enable NRC geologists to assess the potential for tectonic and non-tectonic surface and near-surface deformation at the site, and to determine whether capable (i.e., Quaternary age) tectonic features occur that may influence site suitability.