Duke Energy has begun shutting down its Brunswick nuclear plant near Wilmington in response to Hurricane Florence, but the Charlotte-based utility company has no plans to take its Harris nuclear plant in Wake County offline when the storm rolls into the middle of the state.
The reason for the disparate treatment: wind speed. Federal law requires nuclear operators to shut down reactors when winds reach hurricane force, which is measured as sustained winds stronger than 73 miles per hour.
A planned shutdown during a hurricane is routine procedure at a nuclear facility in the path of an oncoming storm. Even though Florence will drench much of the East Coast, Brunswick is the only nuclear site that is planning to go offline, according to the Nuclear Regulatory Commission.
“It is doubtful that sustained hurricane winds will reach Harris but if the scenario was there, we’d conduct an orderly shutdown,” said Duke spokeswoman Mary Kathryn Green by email.
If the Harris plant does go down, it will be for an entirely different reason: a blackout.
Duke’s 31-year-old Harris nuclear plant in Wake County can generate 928 megawatts of electricity, enough to power a half-million homes.
But all the electricity Harris puts out won’t be enough to keep even a night light running at the nuclear plant if a power outage cuts off the facility from the power grid. If off-site power does go out, the Harris plant’s single nuclear reactor will trip off and go to sleep until the lights come back on.
A power outage is the most likely way that Hurricane Florence will make itself felt at the Harris nuclear plant this weekend. The threats of flooding and wind damage are remote for the Harris site.
Gusts will likely be strong enough, when combined with waterlogged ground, to topple trees into power lines and snap utility poles. Duke said Wednesday that as many as three-fourths of its customers in North Carolina and South Carolina could lose power during the storm.
A nuclear power plant depends on electricity to operate its water pumps, heavy equipment and control room. The plant does not produce its own power, however; rather, it draws from the power grid, like anyone else. If the grid goes out, then the nuclear plant has nowhere to send its power output, and no source of juice it needs to function other than emergency backup generators.
“The power used to operate all equipment in the plant while it is producing electricity would not be available,” said Roger Hannah, a spokesman for the Nuclear Regulatory Commission. “The plant would switch to diesel generators to power a more limited number of systems designed to shut the plant down and keep the fuel in the reactor cool.”
The Harris nuclear plant typically operates round-the-clock for months a a time without interruption. Located in the community of New Hill about 22 miles southwest of Raleigh, the 11,000-acre complex was formerly known as the Shearon Harris plant and contains a single nuclear reactor as well as four spent fuel pools that hold radioactive nuclear waste generated at several Duke nuclear plants.
The reactor core and nuclear waste must be cooled at all times with vast amounts of water.
The NRC’s Hannah said Harris work crews are making final preparations in advance of the looming storm. They are testing emergency backup diesel generators, verifying fuel supplies, testing emergency communications and arranging for backup staff if scheduled employees are unable to get to work after the storm passes.
Diesel generators are required by NRC safety specifications to operate pumps and other critical equipment to cool the reactor’s nuclear core and radioactive nuclear fuel if the facility loses off-site power.
Hannah said the diesel generators would also be used to manage a planned shutdown during a power blackout.
“The diesels are designed to provide power to safety systems needed to shut the reactor down, keep it in a stable condition and cool it down,” Hannah said by email. “It is designed to trip offline automatically if off-site power is lost.”
Green, the Duke spokeswoman, said the Harris plant “is in a good position to weather this hurricane.”
The NRC recently assessed the Harris plant for hurricane preparedness. The federal agency said in a 2017 report that a nuclear plant faces three storm risk scenarios: flooding from intense rainfall, flooding in nearby streams and rivers, and flooding from storm surge. The report noted that the Harris plant is 260 feet above sea level and is safe from the common flooding risks.
The Harris plant is safer today than it was in 2012, when Duke identified and fixed a number of safety concerns discovered in the wake of the 2011 nuclear accident at the Fukushima Daiichi plant in Japan. In that accident, three reactors experienced a partial meltdown and released radioactivity into the atmosphere.
Duke notified the NRC in 2012 that after the Fukushima accident it conducted an inspection at Harris and identified a number of deficiencies. They were largely related to aging and malfunctioning seals needed to waterproof critical areas.