Seismic Risk Analysis and Design of Nuclear Power Plants

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Earthquakes are among the most destructive natural disasters. In response to the occurrence of several destructive earthquakes in recent decades, the nuclear industry is taking a critical look at the existing methods of assessing seismic risk of nuclear power plants (NPPs). A number of deficiencies have been recognized in the existing methods of seismic risk analysis. In an NPP, there are a large number of safety-related structures, systems, and components (SSCs). The most effective approach to ensure safe shutdown and to prevent accidents during an earthquake is to ensure adequate safety margins for these SSCs through seismic design and seismic risk assessment. The long-term objective of my research program is to establish a systematic framework for probabilistic seismic risk analysis and design of NPPs. Through continued collaboration with nuclear industrial partners, the proposed research will satisfactorily address two important issues that have challenged earthquake engineering and the nuclear industry for decades: (1) Generating drift-free, consistent, and perfectly spectra-compatible tri-directional time histories; (2) A direct method for generating Floor Response Spectra (FRS) with flexible foundation and considering soil-structure interaction (SSI).Time history analysis has been widely used in practice, for example, in nonlinear dynamic analysis and analysis of multi-supported systems. Using eigenfunction expansions and the method of influence matrix, the proposed research will develop an efficient and easy to use algorithm to generate drift-free, consistent, and perfectly spectra-compatible tri-directional ground motion time histories. The algorithms and software developed are of great practical importance in earthquake engineering.Accurate determination of FRS, used as a seismic input to SSCs, is one of the most critical tasks in seismic analysis. Overly conservative FRS increase the cost, while non-conservative FRS compromise safety. A direct spectra-to-spectra method for generating FRS that is accurate and efficient has recently been developed by my research group. It is suitable for generating FRS for fixed-base structural models and has been successfully applied in a commercial project by Candu Energy Inc. In the proposed research, the direct method will be extended to account for flexible foundation and SSI. The effect of the uncertainty of soil properties on SSI analysis will be accurately addressed and a complete probabilistic method will be developed to model the uncertainty. This research will provide advanced methodologies and modern tools to assess seismic margin and risk of existing SSCs in refurbished NPPs and to design new SSCs in new NPPs to ensure seismic safety.Close collaborations with the industry will enable HQP to gain both theoretical knowledge and practical experience and make them well qualified for advanced work placements.