(Reuters) - Several nuclear power reactors in North and South Carolina and Virginia on Tuesday started to prepare for Hurricane Florence, which is expected to hit the coast as a major hurricane on Friday.

The storm threatened to make landfall with massive waves and winds of up to 130 mile per hour (209 km per hour), making it a Category 3 or 4 storm on a five-step scale, the National Hurricane Center in Miami warned.

There are 16 nuclear reactors in North Carolina, South Carolina and Virginia, the states expected to suffer the most damage from Florence.

Florence will most likely affect Duke Energy Corp’s 1,870-megawatt (MW) Brunswick and 932-MW Harris nuclear plants in North Carolina and, if it turns north, Dominion Energy Inc’s 1,676-MW Surry plant in Virginia, Roger Hannah, spokesman for the U.S. Nuclear Regulatory Commission’s (NRC) Region 2 office in Atlanta said on Tuesday.

One megawatt can power about 1,000 U.S. homes.

Duke said it could take days to several weeks to restore power to all customers after a storm like Florence depending on the extent of damage and post-storm conditions.

“We anticipate Hurricane Florence to be a historic storm that will impact all customers,” said Grace Rountree, a spokeswoman for the company. Duke serves 4 million customers in the Carolinas.

Duke’s Brunswick nuclear plant is located near Southport, which is close to where Florence is expected to hit. It is about 4 miles (6 km) from the coast and about 30 miles south of Wilmington, North Carolina. The NRC said in a 2004 report that all of the safety-related structures at Brunswick were waterproof up to 22 feet (6.7 meters) above sea level.

Several hurricanes have passed close to Brunswick since the two reactors there entered service in 1975 and 1977, including Hurricane Fran in 1996 and Diana in 1984, both Category 3 storms. Hurricane Hugo, a powerful Category 4 storm, made landfall about 150 miles southwest of Brunswick in South Carolina in 1989.

Duke spokeswoman Mary Kathryn Green said that since the accident at the Fukushima nuclear plant in Japan in 2011 all U.S. nuclear plants have installed more safety equipment, including portable pumps and generators.

To prepare for the storm, nuclear operators check on backup diesel generators to make sure they have enough fuel, conduct site walk downs and secure any loose equipment that could become a projectile in the wind, said Hannah at the NRC.

“Most of the plants have gone through or are going through their pre-storm preparations now,” Hannah said.

About 12 hours before the hurricane arrives, the reactors at the nuclear plants will be shut down, Hannah said.