Davis–Besse is running again, generating 7.7 billion kilowatt-hours of electricity in 2007, with a new reactor head scavenged from an uncompleted nuclear power plant in Michigan. "The NRC has no concerns," Burnell says.
Davis–Besse and FirstEnergy are not alone. Since 1979, after Three Mile Island partially melted down, U.S. nuclear reactors have had to shut down for a year or more for repairs or other safety improvements 46 times, according to the Union of Concerned Scientists. For example, in February 2000 a steam generator tube abruptly ruptured at the Indian Point nuclear power plant in Buchanan, N.Y.—a potential problem first identified in 1997 that had not been fixed.
All told, only four incidents in the history of the nuclear power industry have been worse than the cavity at Davis–Besse, and two have been roughly equivalent, according to the NRC, such as a radioactive steam pipe burst at PSEG's Salem nuclear generating station in New Jersey.
Even as the U.S. considers building as many as 26 new reactors, 51 of the 104 currently operating have received clearance from the NRC to extend their generating lives by 20 or more years. And the remainder are either under review by the agency or expected to apply. The question: Are they safe?
Inside the bathtub
At issue in the failure at Davis–Besse is the alloy metal used to craft the nozzles—known as Inconel 600 or Alloy 600. The alloy of nickel, chromium and iron is resistant to corrosion generally—but slowly cracks when exposed to boric acid and stress.
But it isn't just reactor heads that are made from the stuff. The steam generators that transfer the heat from the solution of water and boron, which comes into contact with the nuclear reactor, to the water heated into steam that turns the turbines to produce electricity also employ the alloy. "The tubes in the steam generators were susceptible to cracking," says Ken Karwoski, senior level advisor for steam generators and material inspection at the NRC's Office of Nuclear Reactor Regulation. "It's a combination of the temperature and the water chemistry."
In the 1970s and 1980s there were several such tubes that actually ruptured, and nuclear operators have employed patches to keep damaged steam generators in service (although this cuts down on the efficiency in generating power). But many have chosen to completely replace their steam generators since 1989 at a cost of as much as $600 million.
As early as the late 1950s there was some suggestion that this metal would crack under pressure but "the decision was made to go with this material," Karwoski says. "The perspective was that it should last but it didn't." And, as of today, there are still 15 nuclear power plants, including Davis–Besse, employing their old steam generators made from the alloy.
The U.S. fleet of 104 nuclear reactors—most built in the 1960s and 1970s—produced 806.5 billion kilowatt-hours of electricity in 2007, a record, and ran almost 92 percent of the time.
But metal fatigue, embrittled concrete (and even rotting wood in the case of Vermont Yankee) have all plagued the nation's aging fleet. Counterintuitively, though, the bulk of problems with these reactors occurred during their first decade of operation—a fact that bodes ill for the next round of nuclear power plant construction. "There will be deficiencies or defects that occur as you start new plants up, even though new plants are simpler and have fewer components," says Adrian Heymer, senior director for strategic programs at the Nuclear Energy Institute, an industry group. "There's always minor adjustments you have to make to the equipment."