We provided fleet-wide flooding subject matter expert (SME) support to Exelon’s thirteen commercial nuclear power plants. The contract included technical oversight and review of all post-Fukushima flood hazard calculations, models, and reports developed by the plants’ Engineers-of-Choice (EOC). In addition, we provided leadership and direction regarding Exelon’s response to the Nuclear Regulatory Commission’s (NRC’s) request for information regarding potential flooding hazards based on lessons learned from the Fukushima Disaster that occurred in Japan in 2011. Aterra’s Vice President and Principal Water Resources Engineer, Joe Bellini, filled the role of flooding SME for Exelon and provided leadership and direction to Exelon’s EOCs in performing Flooding Walkdowns to assess flood protection features relative to the plant’s Design Basis; Flooding Reevaluations, including development of site-specific probable maximum precipitation (PMP) studies, hydrologic modeling, steady flow, and unsteady flow, one-dimensional and two-dimensional hydraulic modeling of the probable maximum flood (PMF), local intense precipitation (LIP) modeling, upstream dam failure, determination of wind waves, run-up, storm surge and hydrodynamic forces; Mitigating Strategy Assessments (MSAs) to determine whether the plant’s flood mitigation strategy is capable of coping with the beyond design basis flooding hazards; and Integrated Assessments (IAs) to determine how non bounded reevaluated flood hazards impact normal plant safety function.
As part of the Conowingo Dam relicensing project, a comprehensive PMF study was conducted to assess the dam’s safety performance. We provided technical input and consultation in developing the PMF, which consisted of a site-specific PMP study and the development and calibration of an HEC-HMS hydrologic model for the Susquehanna River watershed, including a rain-on-snow calibration and flood scenario.
We also completed flood impact assessments at ten of Exelon’s plants, needed to further assess the potential impact to the plant from non-bounded flood hazards identified during the flood hazard reevaluation. The goal was to assess whether the existing flood protection features are both reliable and provide adequate margin. The assessments involved probabilistic flood hazard assessments; evaluation of plant response, time-dependent actions, and flood forecast procedures; and engineering evaluations of flood protection features including walls, pumps, seals, etc.
More broadly, Aterra employees have had significant involvement in post-Fukushima flood hazards, mitigation strategy, and impact assessment support to the entire nuclear industry. Aterra staff actively participated in the Nuclear Energy Institute (NEI) working groups, including the Fukushima Flooding Task Force and Dam Failure and Flood Impact Assessment Sub- Teams. Aterra also partnered with Jensen Hughes in authoring flooding-related guidance documents for the Electric Power Research Institute (EPRI), including “Evaluation of Deterministic Approaches to Characterizing Flood Hazards” and “External Flooding Probabilistic Risk Assessment Walk down Guidance”.
Aterra’s unique combination of substantial hydrologic and hydraulic analysis experience, flood control, dam assessment, and in-depth understanding of post-Fukushima-related regulations and guidance has allowed us to provide unparalleled flooding SME support to Exelon and our other nuclear industry clients.