Report: Nuclear Plant Failed to Prevent Flooding During Ida

Operators of the Millstone nuclear power complex in Connecticut were too late in activating storm protection protocols when the remnants of Hurricane Ida hit the East Coast in September, resulting in minor flooding at the plant, federal regulators said Friday.

The Nuclear Regulatory Commission report said Dominion Energy, which runs the Millstone plant in Waterford along Long Island Sound, violated federal requirements, but deemed the violations of “very low safety significance” and did not issue penalties. The flooding did not affect any nuclear or safety equipment, the report said.

The commission, however, said Dominion’s “performance deficiency was more than minor” and that “required steps to protect risk significant structures, systems, and components from external flooding were not taken until after the consequential rainfall event was in progress.”

Ken Holt, a spokesperson for Dominion, said the company was not contesting the findings of violations. He said operators at the plant initially relied on a forecast from the National Weather Service that predicted rainfall amounts below the level that requires activation of flood control measures at the plant. That level is 3 inches over a six-hour period.

But the operators received a different forecast with a higher rainfall prediction later in the day from state emergency management officials that prompted the closure of flood gates and other safety protocols, Holt said. In the future, operators will have access to multiple forecasts to prevent similar problems, he said.

“The operators at Unit 2 were obviously monitoring the incoming inclement weather,” Holt said. “They were using the National Weather Service data, and that forecast was not predicting a local intense precipitation event.’ And so the operators were following the procedures.”

The remnants of Hurricane Ida blew through the mid-Atlantic states on Sept. 1. At least 50 people were killed in six Eastern states, including a state trooper in Connecticut, as record rainfall overwhelmed rivers and sewer systems, flooded roads and damaged homes.

About 3.6 inches of rain fell at Groton-New London Airport, not far from Millstone, according to the National Weather Service. Holt said 3 inches of rain did not fall within six hours in Waterford during the storm, so it ended up being below the level that requires flood safety measures.

Millstone has two operating nuclear reactors that provide electricity to New England, enough to power 2 million homes.

The Nuclear Regulatory Commission report said the plant’s operators should have activated flood prevention measures before the storm hit, including closing flood gates, based on forecasts made earlier in the day. But they did not do so until after 8 p.m., when heavy rains already were falling. Two flood gates were not closed at all during the storm, resulting in minor flooding in an area near the Unit 2 reactor, the report said.

The commission said Dominion “did not take timely actions to place the plant in a safe condition prior to the arrival of a major storm.”

In another finding of violations deemed of “very low safety significance,” the commission said in the same report that two Millstone workers were exposed to higher radiation levels than expected while performing maintenance at the Unit 3 reactor in June. Regulators said the workers both set off contamination alarms when leaving the work area and required skin decontamination.

According to the report and data from the commission, the workers were exposed to levels of radiation that were below exposure levels typically seen during certain medical scans, including CT scans. Holt said Dominion is taking steps to prevent similar incidents in the future.