Recommendations for Enhancing Reactor Safety in the 21st Century

Near-Term Task Force report issued in the wake of the Great East Japan Earthquake and tsunami of 2011 and ensuing radioactive releases from the Fukushima Dai-ichi Nuclear Power Plant addresses risks of flooding due to dam failures, noting a 1996 NRC requirement, “Factors To Be Considered When Evaluating Sites,” included evaluation of the nature and proximity of man-related hazards, such as dams, for applications submitted on or after January 10, 1997. This regulation was not applied to existing reactors. In August 2010, the NRC initiated a proposed generic issue regarding flooding of nuclear power plant sites following upstream dam failures. Staff evaluation of this issue was incomplete at the time of this report, but the the Task Force concludes that the NRC has inconsistently addressed potential dam failures in the establishment of the design-basis flood. In some cases, emphasis was placed on dam failures coincident with seismic events, while other mechanisms for dam failures were not fully considered. As safety consequences of a flooding event may increase sharply with a small increase in the flooding level, licensees should consider all appropriate internal and external flooding sources, including the effects from local intense precipitation on the site, PMF on streams and rivers, storm surges, seiches, tsunamis, and dam failures. New flooding hazard data and models should be used in regular continuing reevaluations.