Electricity generator Florida Power & Light said on Thursday it will shut its two nuclear power plants before Irma comes ashore as a very powerful hurricane.
FPL, a subsidiary of NextEra Energy, generates enough power for about 1.9 million homes at the Turkey Point and St. Lucie plants, which are both along Florida's Atlantic Coast, about 20 feet (6 meters) above sea level.
"We will safely shut down these nuclear plants well in advance of hurricane-force winds, and we've finalized plans for that shutdown," FPL spokesman Rob Gould told a news conference.
The company will adjust the plans as necessary, "depending upon the path of the storm," Gould said. He would not comment on exactly when the plants would be taken down or how long they could be shut.
The Energy Department said late on Thursday that the Nuclear Regulatory Commission expects Turkey Point to close on Friday evening and St. Lucie to shut about 12 hours later, depending on the storm's path.
Irma is a Category 4 hurricane, near the top of the Saffir-Simpson Hurricane Wind Scale, packing winds of 155 mph (250 km per hour), the National Hurricane Center said in an advisory.
Present forecast models are showing it hitting the tip of Florida on Sunday morning and raking the whole state as it moves north over the peninsula the following couple of days, the Miami-based National Hurricane Center said.
FPL says it has invested $3 billion to protect its electricity grid since 2005, when the last major hurricane damaged power facilities in Florida. But no grid is hurricane-proof, and if Irma stays on its path, many FPL customers will lose power, Gould said.
The company, which serves about 10 million power customers across nearly half of Florida, may have to physically rebuild parts of the power system, Gould said. This could take weeks or longer "if Irma's worst fears are realized," he said.
Gould said FPL might have to turn off some substations ahead of any major flooding, a technique that could help the company restore power faster once any floodwaters recede, rather than keeping them on and allowing the storm to damage them.
FPL's nuclear plants are protected by thick concrete and reinforced steel and like many plants around the world were bolstered further after the 2011 Fukushima nuclear disaster in Japan, Gould said.
A series of explosions and meltdowns occurred at the Fukushima nuclear plant after a massive earthquake unleashed a powerful tsunami that shut the facility's cooling systems and led to meltdowns.
—CNBC contributed to this report.