U.S. Orders Checks for Corrosion at Nuclear Reactors
By MATTHEW L. WALD
WASHINGTON, March 25 - Nuclear reactor operators have been ordered to check their reactor vessels after the discovery that acid in cooling water had eaten a hole nearly all the way through the six-inch-thick lid of a reactor at a plant in Ohio. The corrosion left only a stainless-steel liner less than a half-inch thick to hold in cooling water under more than 2,200 pounds of pressure per square inch.
At the 25-year-old Ohio plant, Davis-Besse, near Toledo, the stainless steel was bent by the pressure and would have broken if corrosion had continued, according to the Nuclear Regulatory Commission, where officials were surprised by the discovery. They said they had never seen so much corrosion in a reactor vessel.
The commission, which has warned plants for years to watch for any corrosion, has ordered all 68 other plants of similar design - pressurized-water reactors - to check their lids. The commission is particularly worried about a dozen of the oldest plants and ordered them to report by early April whether they were safe enough to keep in service. The commission told these plants to demonstrate that technicians there would have noticed such corrosion in their normal inspections, had it occurred.
If the liner had given way in the Ohio reactor, experts say, there would have been an immediate release of thousands of gallons of slightly radioactive and extremely hot water inside the reactor's containment building.
The plants have pipe systems that are meant to pump water back into a leaking vessel, but some experts fear that if rushing steam and water damaged thermal insulation on top of the vessel, the pipes could clog. In that event, the reactor might have lost cooling water and suffered core damage - possibly a meltdown - and a larger release of radiation, at least inside the building.
Such extensive corrosion "was never considered a credible type of concern," said Brian W. Sheron, associate director for project licensing and technology assessment at the regulatory commission....
<http://www.nytimes.com/2002/03/26/national/26NUKE.html> -- Yoshie
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