Defense Date


Document Type


Degree Name

Doctor of Philosophy


Mechanical and Nuclear Engineering

First Advisor

Dr. Zeyun Wu


Natural hazard accidents, especially the Fukushima Daiichi accident that occurred in 2011, have brought up significant safety concerns regarding the nuclear power plant (NPP) under external natural hazards. As a result, external natural hazards have been identified as one of the potentially most significant risk contributors to the core damage frequency of the NPPs, highlighting the need for a better understanding of the natural hazards and their associated uncertainties for probability risk assessments (PRAs). However, there are limited computational models and analysis tools to support the probabilistic evaluation of external hazards in PRAs, especially for natural hazards such as floods due to their spatially and temporally dynamic nature of physical impacts. Furthermore, limited access to relevant information on the hazards also presents considerable challenges to modeling these impacts within a PRA structure.

To address these challenges, the research presented in the dissertation suggested and developed an integrated assessment framework to assess the risks associated with external flooding hazards in NPPs. The framework integrates external flooding events with hybrid NPP response models to provide a more accurate and realistic assessment of potential risks. The first part of the plant response module develops a mechanistic computational model to estimate the event progressions of a generic pressurized water reactor (PWR) NPP under various external flooding scenarios. The second part of the plant response model integrates the developed mechanistic model with an external flooding PRA model developed in this dissertation, which encompasses uncertainties associated with various input parameters.

To demonstrate the effectiveness of the integrated risk assessment framework, a case study was conducted to investigate significant risk scenarios triggered by external flooding events. Specifically, the study examined the potential consequences of short-term and long-term station blackout scenarios for a generic PWR NPP. The results of the case study indicate that the framework is capable of providing a more comprehensive and accurate evaluation of the risks associated with external flooding events. The external flooding PRA models offer a probabilistic assessment of the external flooding risks. Meanwhile, the mechanistic analysis provides a more detailed understanding of the physical phenomena involved in the scenarios and the effectiveness of mitigation strategies. By integrating the PRA and mechanistic analysis, the developed framework offers a more comprehensive and accurate evaluation platform to assess the risks associated with external flooding events, which is critical for decision-making regarding NPP safety.


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Available for download on Friday, May 10, 2024