Dam Failures and Flooding at US Nuclear Plants

October 19, 2012
David Wright
Former contributor

Some 34 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 a Nuclear Regulatory Commission (NRC) staff report written 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 Perkins, accused the NRC of deliberately whiting out passages before releasing the report in response to a Freedom of Information Act request. Perkins suggested in a letter to the NRC inspector general 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.”

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.

An article today by Tom Zeller in the Huffington Post posted the unredacted July 2011 NRC report. The report shows the risk of a nuclear accident from flooding appears to be greater than previously thought.

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 8 to 9 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. 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.

The 8 plants the report identified as among the most vulnerable to a flood caused by a dam failure are Arkansas Nuclear, Cooper, Fort Calhoun, Indian Point, Oconee, Sequoyah, South Texas, and Watts Bar.

The NRC needs to take this known risk more seriously than it has over the past 15 years. It must require plants to address known flooding hazards, and must thoroughly investigate other plants that may be at risk and require them to resolve any potential hazards.

Dave Lochbaum has commented:

“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?”

Click here for our briefing paper on the flooding issue.