DOE Natural Phenomena Hazards Analysis: Establishing an Approach for Probabilistic Flood Hazard Assessment

In 2012, the Department of Energy issued the new standard for Natural Phenomena Hazards Analysis and Design Criteria for DOE Facilities for design of facility structures, systems, and components (SSCs) relating to safety critical functions. This standard established the criteria and guidance for performing natural phenomena hazard analysis on new DOE facilities and modifications of existing facilities in compliance with DOE Order 420.1, Facility Safety. The standard focuses on natural phenomena including earthquake, tornado, volcano, precipitation, and flood hazards. The 2012 revision of the standard moved away from a deterministic approach toward a probabilistic assessment, which has put new challenges on the technical community to establish a framework to execute the requirements of the standard. This approach is being used at nuclear and DOE facilities across the United States for assessing safety critical facility hazards, and in some cases requires assessment of combinations of natural phenomena hazards.This paper will provide an overview of the flood hazard phenomena requirements, address parameter uncertainty, and discuss the framework for establishing a probabilistic approach for flood hazards as specified in the Natural Phenomena Hazards Analysis and Design Criteria for DOE Facilities standard. This includes establishing the flood design category (FDC), performing site characterization, and assessing flood design parameters for establishing the design basis flood level (DBFL). The methodology and modeling approach used to determine flood levels for up to the 100,000 year return period will be discussed. This approach can be applied to new facilities and used to determine impact on existing safety critical facilities.