Seismic Isolation of a Nuclear Structure: Impacts on Construction Cost and Seismic Risk

Base isolation will substantially reduce horizontal seismic demands in structures, systems and components (SSCs) in nuclear facilities, thus providing opportunities to increase seismic safety and reduce construction cost. Although past studies have characterized the benefits of seismic isolation in terms of increased safety, the possible reductions in construction cost have not been quantified. The over excavation, additional reinforced concrete basemat and the seismic bearings will add to the construction cost, but net savings are possible because the required robustness (and thus cost) of the SSCs is much smaller. Some of these issues are explored using a Generic Nuclear Facility (GNF). Nonlinear dynamic analysis of the GNF is performed for the conventionally founded GNF and an isolated variant of the GNF, for the low-to-moderate seismic hazard site of the Idaho National Laboratory and the high seismic hazard site of the Los Alamos National Laboratory. The building is populated with components routinely found in nuclear facilities, and for which fragility data are available. Analysis is performed per ASCE 4-16 to size the seismic isolators. Seismic risk calculations are performed using seismic probabilistic risk assessment methodology proposed by Huang et al. Two procedures are used to assess system functionality: a simplified method based on Boolean algebra and probability theory, and a rigorous Monte Carlo procedure. The cost to construct the GNF is reduced at both sites when isolation is implemented, with greater savings at the LANL site. The simplified method for assessing system functionality provides reliable estimates of risk and is suitable for use in the early stages of nuclear facility design.