The Nuclear Regulatory Commission said Friday that it has asked Exelon Generation to address concerns over how the company would handle a catastrophic flood at the Dresden Nuclear Station in northern Illinois, after recent inspections indicated potential problems.
Among the concerns is how the company would refuel diesel pumps that circulate water to cool the reactor and how it would keep equipment from becoming clogged with flood debris, NRC spokeswoman Viktoria Mitlyng said. The commission sent a letter to the company Thursday, and Exelon has 30 days to respond.
"We're not saying their plan won't work, but we have raised questions," and Exelon must demonstrate that it would work, Mitlyng said.
She said there is no immediate safety risk, but the goal is to keep the site's two reactors safe in the event of a worst-case flood, like the one that swamped the Fukushima Daiichi plant in Japan last year.
Although that is highly improbable, the company must be prepared, Mitlyng said.
Exelon spokeswoman Krista Lopykinski said the company still is reviewing the NRC's questions but has taken steps to upgrade flood security to reflect "lessons learned" from the disaster at Fukushima.
Those steps included buying a portable 8-foot-high dam, portable diesel water pumps and backup generators. Exelon also is reviewing potential plant modifications, officials said. The company plans to hold a public meeting at the plant on Dec. 15 to answer residents' questions.
"Maintaining safety at Dresden, even under the most severe circumstances, is our number one priority," site Vice President Dave Czufin said in a written statement.
The plant is in Morris, at the confluence of the Des Plaines, Illinois and Kankakee rivers.
Plant operators and the NRC have been inspecting the nation's nuclear plants in the wake of the Fukushima disaster. The Dresden reactors are the same design as those at Fukushima, with ground-level emergency generators and spent fuel rods stored above and outside the reactor containment chamber.
The plant was built at 517 feet above sea level, or 10 feet above historic flood levels. But updated modeling indicates the worst-case flood could be 528 feet above sea level.
There has never been a flood that high. But with changing weather patterns, Mitlyng said, "events have been taking place ... beyond what we expect or what has been known."
The Dresden reactors were licensed in 1966 and are among the oldest in the U.S. They surpassed their original 40-year life spans and have been granted 20-year license extensions.
Exelon operates all 11 nuclear power reactors in Illinois. Dresden is the only one for which the NRC raised flooding concerns, Mitlyng said.