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.Skip to next paragraph
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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.