Seismic isolation of nuclear reactor vessels considering soil-structure interaction
Creators: name: Shrestha, Samyog
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Structural engineering
Civil geotechnical engineering

description: The research presented in this dissertation investigates the influence of soil-structure<br> interaction on seismic isolation of nuclear reactor vessels using numerical simulations. This<br> research is motivated by the nuclear industry searching for viable solutions to standardize<br> the design of reactor vessels. Seismic isolation of reactor vessels is a potential solution as it<br> enables deployment of standardized reactor vessels irrespective of site seismic hazard<br> thereby saving time and cost by allowing large-scale factory fabrication of standard<br> modules and by eliminating the need for repeated approval of reactor vessel design. Seismic<br> isolation is also a technology that has matured from successful implementation in buildings<br> and bridges allowing easier transition to nuclear applications. Currently, the<br> implementation of component-level seismic isolation in nuclear industry is challenging due<br> to gaps in research and lack of specific guidelines. <br> <br> In this research, the effectiveness and potential limitations of using conventional friction<br> pendulum bearings for component-level isolation are investigated based on conceptual<br> numerical models of seismically isolated reactor vessels at different nuclear power plant<br> sites subject to a variety of ground motions. The numerical modeling and analysis<br> approach presented in this research are checked using experimental data and results from<br> multiple numerical codes to ensure reliability of the obtained analysis results. <br> <br> Within the scope of this study, it is found that slender vessels are particularly vulnerable<br> to rotational acceleration at the isolation interface. Rotational acceleration at the isolation<br> interface is caused by rotation at the foundation level of the containment building housing<br> the isolated reactor vessel and by excitation of higher horizontal translational modes of the<br> seismically isolated system. Rotation of the building foundation increases with decrease in<br> shear wave velocity of the soil surrounding the building foundation. When the containment<br> building is embedded below the soil surface, the effect of embedment on peak horizontal<br> acceleration of the isolated vessel depends on the amount of increase in shear wave velocity<br> at the foundation level of the building. When embedment does not result in any change in<br> shear wave velocity, it is found to have negligible impact on the acceleration response of the<br> isolated vessel. <br> The optimum location to support a vessel for seismic isolation is found to be on a plane<br> passing through its center of mass. It minimizes horizontal acceleration in the isolated<br> vessel as well as the tendency of isolator to uplift. Isolator uplift and exceedence of<br> displacement capacity of the isolator during extreme events are possible drawbacks in using<br> seismic isolation technology since they produce impact forces due to uplift and<br> re-engagement of the isolator or due to collision between the isolated system and the moat<br> wall. If such cases are avoided, seismic isolation of reactor vessel could provide more than<br> 50% reduction in peak acceleration of vessel except for low-intensity motions that do not<br> engage the isolator.<br> <br>