Towards standardized nuclear reactors: Seismic isolation and the cost impact of the earthquake load case
Advanced nuclear reactors have a key role to play in global decarbonization. Impediments to the widespread deployment of advanced reactors is their projected high overnight capital cost (OCC) and levelized cost of energy, and time required to analyze, design, license, construct, and commission. The earthquake load case is one of the key cost drivers for a new build nuclear plant, because near-surface soils and seismic hazard are different at each site, requiring site-specific analysis, design, engineering, qualification, licensing, and regulatory review, essentially making every design First-of-a-Kind (FoaK). To enable deployment at the scale needed for deep decarbonization, the cost and time impact of the seismic load case must be significantly reduced or eliminated, and plants must be standardized. Seismic base isolation has been proven to considerably reduce the earthquake response of structures and equipment but has yet to be applied to a nuclear power plant in the United States, in part because the financial impacts, positive or negative, are not known. Because no modern, non-proprietary data exist to characterize the influence of the seismic load case on OCC, it is impossible to confidently quantify the financial benefits of seismic isolation. To assemble modern cost data on the influence of the seismic load case, scheme designs of two fundamentally different advanced reactor buildings were developed. Both buildings were equipped with three bespoke pieces of safety-class equipment and analyzed for incremented levels of earthquake shaking to quantify the seismic penalty on equipment, in terms of vessel weights and horizontal accelerations. Using analysis results, a questionnaire was developed and transmitted to domain experts to collect cost data on engineering and fabrication costs for these unique pieces of safety-class equipment. Synthesis of the cost data showed that the seismic load case significantly affects the capital cost (sum of engineering and fabrication cost) of safety-class equipment, with engineering costs being comparable to fabrication costs. Standardization of safety-class equipment is made possible by seismic isolation, that is, equipment designed for minimal seismic robustness can resist earthquake shaking at a site of much higher seismic hazard. The predicted average reduction in capital cost enabled by seismic isolation is a factor of two for FoaK equipment and a factor of five for standardized equipment.