Nuclear Regulatory Commission Report Reveals Greater Flood Risk to 34 Nuclear Plants

The uncensored NRC report finds that upstream dam failure and the resultant flood risk to nuclear reactors is higher than previously reported.
From The Union of Concerned Scientists
October 19, 2012
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The NRC has failed to report what it has known for years, that an upstream dam failure could result in a flood threat to downstream nuclear reactors.
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This article is posted with permission from The Union of Concerned Scientists.

The Huffington Post published an article today revealing details of a censored Nuclear Regulatory Commission (NRC) report showing the risk of a flooding accident at U.S. nuclear power plants appears to be greater than previously thought.

Thirty-four nuclear reactors — one-third of the U.S. fleet — could face flooding hazards greater than they were designed to withstand if an upstream dam fails, according to the report, which was written by NRC staff member in July of last year. The NRC has known about these risks for at least 15 years and has failed to adequately address them.

The report generated attention a month ago when its lead author, Richard H. Perkins, accused the NRC of deliberately whiting out passages before releasing the report in response to a Freedom of Information Act request to avoid embarrassment. In a letter submitted to the NRC inspector general on September 14, Perkins suggested that the NRC censored his report because it reveals “the NRC has been in possession of relevant, notable, and derogatory safety information for an extended period but failed to properly act on it.”

The flooding threat is due to the fact that nuclear reactors are built adjacent to rivers, lakes and oceans because they require vast quantities of cooling water. Many U.S. nuclear plants that are sited along a river have one or more dams located upstream. If a dam failed, the ensuing flood waters could overwhelm a plant’s protective barriers and disable critical safety equipment, causing an accident that could release a large amount of radiation, just as it did at the Fukushima Daiichi plant in Japan in March 2011. In that case, the flooding was caused by a tsunami, not a breached dam, but the result could be similar. (For more information on flooding risks, see the Union of Concerned Scientists’ new fact sheet, “Dam Failures and Flooding at U.S. Nuclear Plants.”)

The Huffington Post provided a link to the unredacted NRC report and described some of what was excised by NRC censors.

For example, the uncensored version of the report includes a section about one of the plants at risk, the Oconee Nuclear Station in South Carolina. It reveals that the plant’s owner, Duke Energy, discovered that a failure of the nearby Jocassee dam could flood the plant and cause the loss of power and safety equipment, potentially damaging its three reactor cores within eight to nine hours. It could further lead to reactor containment failure within 59 to 68 hours, triggering a significant release of radioactivity into the environment. Duke informed the NRC about this flooding hazard as early as January 1996.

The unredacted version also reveals that the failure probability of dams like Jocassee that the NRC uses in its analyses is 20 times larger than that used by Duke Energy.

In a section about the Fort Calhoun plant in Nebraska, NRC censors removed a label on a graph that indicates the failure of the Oahe or Fort Randall dams under certain conditions could result in water levels higher than the plant’s flood protection structures . The report also states that “Fort Calhoun Station may not have been protected from flooding even without consideration of upstream dam failure. An upstream dam failure further exacerbates this condition.”

Another whited-out section in the report called for Cooper Nuclear Station in Nebraska to be re-evaluated to determine if it is as vulnerable to flooding as Fort Calhoun.

Below is a list of eight plants the report identified as some of the most vulnerable to a flood from a dam failure and the nearest metropolitan areas to those plants.

  • Arkansas Nuclear: Little Rock
  • Cooper: Kansas City, Lincoln and Omaha
  • Fort Calhoun: Omaha
  • Indian Point: Bridgeport, Danbury, New Haven, New York City, Poughkeepsie and Stamford
  • Oconee: Greenville (S.C.)
  • Sequoyah: Chattanooga
  • South Texas: Houston, San Antonio and Austin
  • Watts Bar: Knoxville

“The NRC knows—and has known for many years—that flooding from dam failures can disable the emergency equipment needed to prevent reactor core meltdown,” said Dave Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists. “The agency must require plants to address known flooding hazards and thoroughly investigate other plants that may be at risk and require them to resolve any potential hazards.

“If such a flooding accident occurred, the NRC would quickly determine which other plants were vulnerable and require them to strengthen their protection against similar events. Wouldn’t it be smarter for the agency to do that before an accident occurs?”

The Union of Concerned Scientists is the leading U.S. science-based nonprofit organization working for a healthy environment and a safer world. Founded in 1969, UCS is headquartered in Cambridge, Massachusetts, and also has offices in Berkeley, Chicago and Washington, D.C. For more information, go to

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