Nuclear Power Plants Losing Steam
Leaks found at a Maine nuclear plant have spurred close inspections of steam-generated plants nationwide
AN inspection of steam generators at a nuclear power plant in Maine has revealed cracks in hundreds of key metal tubes, prompting a federal demand for similar inspections at plants nationwide.
The Nuclear Regulatory Commission is sending out the order as early as this week, according to Brian Sheron, director of the engineering division within the agency's Office of Nuclear Reactor Regulation.
''We're asking plants to test the tubing in their steam generators at their next scheduled outage,'' he says. ''In the interim, we're asking them to tell us why they believe their plants are safe to operate.''
The move highlights a long-simmering problem within the nuclear industry -- one that has forced at least two plants to shut down permanently well before their operating licenses expired.
Meanwhile, it is leading to deep fissures within an industry that often shows a solid front to the public. Utilities from coast to coast have filed more than a dozen lawsuits -- some alleging fraud -- against Westinghouse Electric Corporation. Westinghouse is one of two leading manufacturers of pressurized-water reactors, which use steam generators in their design.
Making safe steam
Pressurized-water reactors are used in 75 out of 108 plants in the United States, according to the Nuclear Energy Institute (NEI) in Washington, D.C. The steam generators, which sit inside the reactor containment building, are huge heat exchangers.
They transfer heat from the coolant flowing through the reactor's core to a secondary loop, which converts water to steam to drive the turbines that generate electricity. Steam generators also isolate the coolant from the secondary loop, preventing radioactive water from circulating through other parts of the plant and escaping into the environment.
The problem: Steam generators are not lasting as long as plant operators expected. The finger-sized tubes through which the radioactive coolant passes in order to convert the water surrounding the tubes to steam show unexpected levels of cracking and corrosion. In some cases, utilities are having to replace one or more of the $50-million components in plants that have been operating for less than a quarter of their 40-year design life.
In the most recent example, officials at the Maine Yankee nuclear power plant near Wiscassett, Maine, announced last week that they would keep the plant shut down indefinitely, following the discovery that as many as half of the 17,000 tubes in its three steam generators could be cracked. The utility is now expanding its inspection from a sample of 500 tubes to the full complement in an attempt to clarify the situation.
''What's intriguing is that these operated well for 22 or 23 years,'' but are suddenly showing widespread cracking, says Marshall Murphy, a spokesman for Maine Yankee. In addition, the plant's technicians used a new type of device for testing the tubes, one that when combined with computer imaging, clearly identifies cracks that have been hard to identify.
Maine Yankee faces a decision, Mr. Sheron says. The flawed tubes cannot be plugged and taken out of service; there are too many of them. Because the tubes are crucial for heat transfer, plugging them would force the plant operators to run the reactor at a much lower power rating, reducing the plant's efficiency and raising the cost of the electricity generated. Technicians could put sleeves down the inside of the faulty tubes, but that also reduces efficiency, though at a slower pace.
Or plant owners could replace generators. But replacing would cost up to $150 million, and the plant's license is set to expire in 2008. Central Maine Power, which operates Maine Yankee, recently reached an agreement with the state not to raise electric rates for five years. Some say the economics could force Central Maine Power to pull the plug on Maine Yankee.
If shut down permanently, Maine Yankee won't be the first plant felled by faulty steam generators. Following tube leaks in November 1992, Portland General Electric in Oregon decided to close the Trojan nuclear power plant for good, purely for business reasons.
''Safety was going to be met, but in doing so we had to be cost-effective'' providers of electricity, spokesman David Heintzman says. When the company looked at the cost of replacing the generators against the costs of buying power from elsewhere and building natural-gas turbine plants, it opted to close Trojan.
The company also decided to sue Westinghouse, which supplied Trojan's reactor. ''Our contention is that this phenomenon [cracking and corrosion] was known when the steam generators were designed,'' Mr. Heintzman says.
It is a position shared by other utilities, including the Duquesne Light Company in Pennsylvania. It sued Westinghouse in federal district court in Pittsburgh last year. In December, after the judge threw out four of the five counts, including fraud, a jury decided in favor of Westinghouse on the fifth count.
On Feb. 28, Duquesne filed an appeal. In the document, the plaintiffs cite what they saw as the trial judge's improper exclusion of evidence and testimony that would have bolstered their contention that Westinghouse's scientists not only knew of the problem, but even suggested that the company misidentify it as being another tube-related flaw that was more well-known.
In all, up to 13 utilities have sued the company, which has 51 of its reactors working in the US, according to the NEI. The majority of cases have been settled out of court and the settlements sealed.
South Texas Project also has legal action pending against Westinghouse. ''We're in a fuel outage and expect a preliminary report on our steam generator tubes soon,'' says a South Texas Project spokesman. ''We've been watching the rest of the industry, and we've filed suit to compel Westinghouse to stand behind its product.''
No industry consensus
The industry is trying to find more effective ways to handle the steam-generator problem. But the jury is still out on the cause. ''There is no consensus within the NRC or the industry,'' says Portland General Electric's Heintzman.
What troubles some, such as Robert Pollard, a former project manager for the Nuclear Regulatory Commission and now a nuclear safety engineer for the Union of Concerned Scientists in Washington, is that even as the problem's causes are unclear and it seems to be spreading, the NRC has proposed changes in tube inspection that raise the threshold for triggering repairs.
The issue has sparked concerns among several of the NRC's technical staff.
When looking at credible accident scenarios, ''the assumption has been that one tube would rupture,'' Heintzman says. ''Now they're having to look at more failure scenarios.''