With Hurricane Florence approaching, Duke Energy has started the process of shutting down its nuclear power plant on the southeastern coast of North Carolina.
Duke is powering down the Brunswick nuclear plant in Southport to comply with standards set by the U.S. Nuclear Regulatory Commission, which require shut downs in the face of winds stronger than 73 miles per hour.
The utility’s meteorologists expect Hurricane Florence to bring 100-mph winds to Brunswick County, said Karen Williams, Duke’s spokeswoman for the plant. Florence will be only the 10th hurricane to come within 50 miles of the plant since 1970, she said.
“We haven’t been forced to shut down for a hurricane in some time,” Williams said, adding that the shut down is standard procedure and plant staff is highly-trained. “We run them through mock scenarios.”
Southport is about 30 miles south of Wilmington. Customers won’t experience power outages as a result of the shut down, she added.
The Brunswick plant is likely to be the only nuclear plant that shuts down as a result of Hurricane Florence, said Roger Hannah, a spokesman for the Nuclear Regulatory Commission.
Brunswick has five on-site diesel generators that are backed up by two additional generators, said Galen Smith, the plant’s on-site resident inspector with the Nuclear Regulatory Commission. During the shut down, the generators will continue to operate the pumps that supply the water needed to cool the reactor core and keep radioactive fuel rods from overheating and triggering a runaway nuclear reaction.
The Brunswick plant is built at an elevation of 20 feet above sea level and designed to withstand a storm surge of 22 feet, which would leave the emergency generators high and dry. Brunswick, which is four miles inland, can withstand maximum sustained winds over 200 miles per hour of a Category 5 hurricane, Williams said.
As far as wind damage goes, Smith said that the structures containing Brunswick’s twin nuclear reactors are virtually impenetrable, enclosed in walls several feet thick that are cast from concrete and rebar.
“We have verified the capability to withstand a total loss of electric power to our plants,” Williams said. “We have verified our capability to withstand flooding and the impact of floods on systems inside and outside the plant.”
At least two NRC inspectors will ride out the storm inside the plant, Smith said, and they have been making rounds daily to monitor the progress as plant operators prepare for the storm.
“They have everything they need to operate the plant safely,” Smith said. “It’s just a matter of executing at this point. Even if the storm is bad, they should do fine.”
Lessons from Fukushima
The 1,200-acre Brunswick plant was built in the 1970s and Florence will likely be the first major test of the safeguards installed at the dual-reactor plant since the 2011 nuclear disaster at the Fukushima Daiichi plant in Japan, which is the same generation and design as the Brunswick plant.
A tsunami flooded Fukushima’s emergency backup generators, cutting off power that was needed to pump water to constantly cool the facility’s radioactive nuclear fuel. Without power, the nuclear fuel overheated in three reactor cores, triggering hydrogen explosions that spewed radioactivity into the atmosphere.
The U.S. Nuclear Regulatory Commission determined after Fukushima that Brunswick is not fully safe without modifications. As a result, Brunswick’s emergency plan now calls for installing nine temporary flood barriers in advance of a hurricane, to compensate for deficiencies in the original design.
“The good news is, because of Fukushima, the plant is better prepared,” said Dave Lochbaum, director of the nuclear safety project for the Union of Concerned Scientists, a watchdog group. “If it hadn’t been for Fukushima, that vulnerability would not have been identified.”
Nuclear plants have consistently proven hardy against hurricanes. Hurricane Andrew, a Category 5 storm, passed directly over the Turkey Point plant in Florida in 1992, causing extensive damage to communications systems and the fire protection system, but the nuclear safety infrastructure remained intact, according to the Union of Concerned Scientists. Several storms have passed close to Brunswick, including Hurricane Fran in 1996, which made landfall as a Category 3 hurricane.
During Hurricane Matthew in 2016, wind speeds never reached hurricane force at the Brunswick site and there was no flooding, Williams said.
A modern fortress guarded by armed security, the Brunswick plant is touted by Duke as one of the most robust type of structures standing in the Unites States. But a year after the Fukushima incident, Duke Energy discovered scores of potential areas of leakage and water penetration at Brunswick that had to be fixed. Duke identified the problems as missing seals, missing or corroded bolts, broken links or pressure plates, corrosion, open terminal boxes, gaps in weather stripping on doors and inadequate repairs for previous leakage.
The temporary flood barriers installed ahead of Florence, called “cliff edge barriers,” hint at the remote potential for catastrophe inherent to the business of splitting atoms to make electricity. In nuclear parlance, a “cliff edge” effect refers to a small variation in plant conditions that can trigger an abrupt change, pushing a nuclear plant over the cliff, from normal functioning to a critical state.
Brunswick’s “cliff edge” barriers will be installed to prevent sea water from gushing through doorways that protect safety equipment and sensitive areas of the plant. The barriers are designed to repel a storm surge of 26 feet, said NRC spokesman Scott Burnell, citing documentation submitted by Duke Energy.
Each barrier consists of an aluminum plate fastened to the wall with stainless steel anchors and backed by a rubber strip to create a waterproof seal. They will be installed at nine doors in the diesel generator building, control building and in the reactor building’s airlock doors. It takes workmen up to 2 1/2 hours to install each barrier, and Duke begins setting up the barriers as soon as a hurricane watch is issued.
The cliff edge barriers are not considered some crude patch job, but a high-tech upgrade. Burnell characterized them as part of Brunswick’s long-term strategy for “dealing with events that might exceed the plant’s original design basis.”