Utilities across the country are exploring a second 20-year license renewal for their nuclear plants.

Duke Energy is exploring the possibility of plants such as Southport's Brunswick Nuclear Plant operating for up to 80 years.

Initially, the federal Nuclear Regulatory Commission issued 40-year licenses for nuclear plants across the country, nearly all of which have applied for 20-year renewals. Now, with the time nearing to begin the nearly decade-long renewal process, many utilities are discussing applying for a second renewal, and four plants have begun the process.

Explaining why the initial license is issued for 40 years, Travis Knight, director of the University of South Carolina's nuclear engineering graduate program, said, "The thought was these (nuclear plants) are going to be obsolete in 40 or 50 years."

That hasn't happened, in part because of the economics of building a nuclear plant, leaving power companies to turn to a renewal process that is grounded in technical aspects such as cabling, the state of the facilities concrete and other components. After walking the N.C. General Assembly's Joint Legislative Committee on Energy Policy through the process earlier this month, Jeff Merrifield, a former member of the Nuclear Regulatory Commission, said the Duke fleet represents "a strong candidate" for renewal.

During the same meeting, T. Preston Gillespie, a senior vice president and the chief nuclear officer of Duke Energy, said nuclear power generation is crucial for the power company to meet carbon targets.

Gillespie also said the company is constantly making upgrades to its plants.

"The plant's always being maintained. Critical pieces of equipment are always being replaced -- we've replaced miles and miles of piping in the plant. If you were to walk into one of our facilities right now, you'd see a very modern, clean plant that has new equipment in it," Gillespie said.

That description holds true at the Brunswick plant in Southport.

According to a plant spokeswoman, Duke completed a refueling outage earlier this year, also installing new turbine controls and completing a four-year project to upgrade the plant's diesel generators that keep the facility operational during emergencies.

Duke's 11 reactors at six sites in North and South Carolina generated more than 56 percent of the two states' power, the spokeswoman said, potentially replacing the release of as much as 82 million metric tons of carbon dioxide last year.

"We believe our plants are good candidates for second license renewal," Karen Williams, spokeswoman for the Brunswick plant, wrote in an email. "We maintain rigorous, ongoing preventive maintenance programs across our generating fleet and have completed many upgrades and investments over the years at all our stations."

Licenses for the two reactors at Brunswick are set to expire in 2034 and 2036.

While the equipment upgrades and replacements that come with re-licensing have costs, they are often much more affordable than building a new plant, Knight said. He also said there are often small pieces of concrete kept inside of nuclear reactors that are taken out and tested to see how the nearby reaction is impacting them.

"Research studies have looked into the technical issues to help utilities ensure that components can serve their intended function or decide which components might need replacement," Knight said. "In regard to both economics and science and engineering, it is a careful and reasoned decision."

The main factor limiting how long a plant could be operational is the reactor vessel itself, which experts say could eventually become brittle because of the nuclear activity taking place inside it.

"That lifetime, "Gillespie said, "is much, much greater than 80 years."

Reporter Adam Wagner can be reached at 910-343-2389 or Adam.Wagner@GateHouseMedia.com.