NRC orders reactor check after near-accident in Ohio

Acid in cooling water corrodes lid of reactor


WASHINGTON - Nuclear reactor operators have been ordered to check reactor vessels after the discovery that acid in cooling water had eaten a hole nearly all the way through the 6-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.

At the 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. Officials said they had never seen so much corrosion in a reactor vessel.

The NRC, which has warned plants for years to watch for this kind of 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 are safe enough to keep in service. The NRC told the plants to demonstrate that their technicians would have noticed such corrosion during normal inspections, had it occurred.

If the liner had given way in the Ohio reactor, experts say, thousands of gallons of slightly radioactive and extremely hot water would have been released in the reactor's containment building.

The plants have systems that are meant to pump water back into a leaking vessel, but some experts fear that if rushing steam and water damaged insulation on top of the vessel, the pipes could clog. In that event, the reactor might lose cooling water and suffer 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 of the Nuclear Regulatory Commission.

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