Washington, DC — A Nuclear Regulatory Commission (NRC) assessment finds six nuclear reactors have “high” vulnerability to flooding from upstream dam failures yet that risk was excluded from prior safety reviews. Reactor operators have yet to fully account for this danger, according to an industry document obtained by Public Employees for Environmental Responsibility (PEER) in a Freedom of Information Act lawsuit against the NRC.
The NRC risk rating is contained in a July 19, 2010 memo entitled “Identification of Generic External Flooding Issue Due to Potential Dam failures” from Lois James, Chief of the Probabilistic Risk Assessment Operational Support Branch, to her chain of command. The following nuclear power plants were found to have a “high” vulnerability to inundation from “dam hazard”:
- Arkansas Nuclear (AR)
- Fort Calhoun (NE)
- McGuire (NC)
- Oconee (SC)
- South Texas (TX)
- Watts Bar (TN)
Another nine reactors in an additional four states (AL, PA, VT and WA) were found to have a “medium” vulnerability to dam-induced flooding. As at Japan’s Fukushima reactor, flooding can render reactor safety systems inoperable, leading to core meltdown and massive releases of radioactive by-products.
In her memo, Ms. James concludes that:
- “Since dam failures were exclude from consideration in most [safety reviews], its risk contribution has not been addressed to date”; and
- “There is an increase in the estimated frequency of a potential dam failure of an order of magnitude” from previous assessments.
“These credible scenarios could lead to cataclysmic consequences,” stated PEER Counsel Kathryn Douglass, who filed the suit producing these and other documents from NRC. “The communities surrounding these plants should start pressing for preventive action tomorrow.”
Utilities owning these reactors have yet to take the dam hazards seriously, however. An April 2011 “Dam Failure Flood Mitigation Strategy” from Duke Energy, operator of the highly vulnerable three-reactor Oconee nuclear complex, limits its preventative actions based upon assumptions such as that dam failure is not “concurrent with an earthquake” or other “design bass accidents, design events or transients.”
“Duke Energy is only willing to plan for a ‘sunny day’ dam break,” Douglass added, noting that storms or other events leading to dam failure would not be addressed by the company’s mitigation strategy. “As Fukushima amply demonstrates, disasters do not always occur in isolation. For all our sakes, the NRC should require reactor operators to plan for worst case scenarios with multiple failures occurring simultaneously.”