ML25178C716
| ML25178C716 | |
| Person / Time | |
|---|---|
| Site: | 99902095 |
| Issue date: | 07/07/2025 |
| From: | NRC/NRR/DANU |
| To: | |
| References | |
| Download: ML25178C716 (1) | |
Text
Observations on Seismic Site Characterization and Seismic Hazard Analysis Purpose The purpose of this appendix is to provide U.S. Nuclear Regulatory Commission (NRC) staff observations of Oklo's preliminary combined license (COL) application (COLA) on certain topics that are either outside the scope of phase I, or within the scope of phase I with a strong dependency on information that will be included in phase II.
Background
The NRC staff identified several observations related to the level of detail and justification for geologic site characterization and seismic hazard analysis required to meet Title 10 of the Code of Federal Regulations (10 CFR) section 100.23, "Geologic and seismic siting criteria." Oklo stated that the level of detail and the sources of seismic hazard models were predicated on the assumption that all structures, s stems, and components (SSCs) would be assigned a seismic design category (SOC) of [
)). Oklo stated that SDC-2 SSCs may be designed to the International Building Co e an SCE 7, which have been applied to research and test reactors (RTRs) but not power reactors. The ASCE 7 method of developing ground motion response spectra (GMRS) specifies the use of spectral accelerations from the U.S. Geological Survey (USGS) national seismic hazard model (NSHM), which the NRC staff has not reviewed or endorsed for use at power reactor sites.
Oklo provided supplemental information in the preli ina COLA phase I to demonstrate that the ASCE ?-derived GMRS is conservative for an [ -
)) at the Idaho National Laboratory (INL) Aurora site. The supplemental informa I0n inc uaed a comparison of the ASCE
?-derived GMRS to the design response spectra (DRS) for SDC-3, -4, and -5 SSCs for the Materials and Fuels Complex (MFC) site from a U.S. Department of Energy (DOE) Senior Seismic Hazard Analysis Committee (SSHAC) level 3 (L3) study performed at INL. While insightful, Oklo clarified that it is seeking approval of the use of the ASCE ?-derived GMRS developed using USGS information and removed the supplemental information in an updated version of the preliminary final safety analysis report (FSAR) shared on April 15, 2025, to improve clarity.
I
Topic #2: Seismic Hazard Analysis Regardless of the source of the seismic hazard model used to develop the GMRS for the INL site, and regardless of the SOC level, Okie should provide sufficient detail and justification for why the model being credited for site ground motion and the underl in data are a licable to the site to meet the re uirements of 1 0 CFR 100.23.
in the scope of phase I of the COLA and is included as an observation in this report.
phase II o I
d through a SSHAC L 1 (or similar) study. The staff note that a description of the process to develop a site-specific GMRS by performing a SSHAC L 1 study and incorporating site-specific data into the regional study may be needed in the FSAR if the facility is SDC-3 -4, or -5.