By CP Staff
By Olivia LaVecchia
By Chris Parker
By Jesse Marx
By John Baichtal
By Olivia LaVecchia
By Jesse Marx
By Olivia LaVecchia
For the industry, steam generators are no marginal matter: They are, after all, at the very core of the process creating electricity out of fissioning atoms. In a pressurized-water reactor like Prairie Island, the radioactive core heats its coolant to 590 degrees; that liquid then runs through more than 6,000 horseshoe-shaped metal pipes, each about 70 feet long and almost an inch in diameter. When you run water along the outside of those pipes it immediately flashes to steam, which is piped to turbines. In a crude analogy, you could imagine the whole thing as a radiator, hooked up to a furnace, sitting in a bathtub. If the radiator breaks, the liquid in it mingles with the bathtub water; if a lot of fluid leaks out, the furnace could overheat.
To keep that from happening, Westinghouse pipes are manufactured from an alloy called Inconel-600, specially designed to the withstand punishing conditions of heat, pressure, and radioactivity. The problem, NSP's and other lawsuits allege, is that it doesn't. Though steam generators are supposed to last 40 years, tubes have been found to start cracking after less than 10 years of service. Engineers don't quite understand how this happens, but they know that the tiny fissures can grow larger and eventually burst.
And it turns out that Westinghouse may have been aware of this for some time--before, in fact, it sold most of its steam generators, including NSP's. (Westinghouse isn't the only company whose steam generators have been giving utilities trouble, but it's the only one so far being sued.) One 1964 Westinghouse memo--quoted in a lawsuit filed by South Carolina's Duke Power Co. in 1990--referred to an employee being told that "he was not to inform anyone with the exception of his boss of the Inconel corrosion problem, to prevent a possible hold on steam generator production." Another company document, dated 1968, showed a researcher's hand-written notation: "What do we tell them at this stage? That [Inconel] is crumbling before our eyes or that service experience is so far good?"
Judging from NSP's records, the former is closer to the truth. A 1991 memo from one of its researchers to the utility-funded Electric Power Institute bluntly noted that steam generators as designed were "a corrosion machine," and "no better than almost good enough" (emphasis in the original). By 1994, NSP had had to shut down its reactors at least eight times due to generator problems. More than 12 percent of a total of 13,500 tubes showed indications of cracking as of this February--enough to force NSP to keep its reactor shut down for two weeks beyond schedule for repairs.
"Repairs," of course, assumes that you know what you're fixing--which, in the case of steam generator troubles, reactor operators don't really. The tubes are inspected by a magnetic probe that travels through them on a cable. More sophisticated probes have been developed over the years, but documents from the lawsuit indicate that utilities aren't always eager to use the latest technology. In a handwritten 1986 note, NSP steam generator expert Richard Pearson summarized discussions with other company officials over a new kind of magnetic probe. It had been suggested, he wrote, that "we should tread very careful and not look for trouble... We don't have freedom to use the probe to look for as much information as possible."
Publicly, power companies have said that they "tread careful" with new testing equipment simply because the gear hasn't had all its kinks worked out yet. But it's also worth noting that anytime a utility has to plug or sleeve a steam generator tube, it loses a little of its power-generating capacity--and, by extension, revenue. "There has been a concern for some time," says Paul Gunter, who follows the issue at the Washington-based Nuclear Information and Resource Service, "that the industry is reluctant to have a full diagnostic done because they're worried about what they might find."
What's been found is enough to worry the Nuclear Regulatory Commission. Bill Russell, director of the agency's Office of Nuclear Reactor Regulation, told members at a recent meeting that "many more cracking indications than anticipated" were being found at plants throughout the country, and that their number was growing exponentially. Cracks would "jump from the tens in one [inspection], to the hundreds--or thousands--in the next." Even the materials used to fix the cracking tubes had been found to deteriorate in turn, forcing utilities to regularly redo earlier repairs.
The NRC and the utilities insist that none of this poses a danger to the public. "Our primary concern," says Brian Sheron, who heads the nuclear regulation office's engineering division, "is that these plants continue to operate with the tubes structurally intact. If that means that a plant has to shut down every five months, or if it means that a plant has to [fix] lots of tubes, then that may not make the utility happy, but it makes the NRC happy."
The utilities, in turn, say nothing makes them happier than going the extra mile for safety--particularly NSP, which now operates one of the oldest steam generators in the industry. Company officials say they've been able to keep the equipment going because of extra-thorough research and maintenance. (Prairie Island is frequently cited as one of the best-run plants nationwide.) "It's become just part of the way we do business," says plant manager Mike Wadley. "It consumes a lot of time and money and anxiety. But it's a manageable situation. And besides, we have defense in depth."