"A nuclear reactor where a hidden leak caused near-catastrophic corrosion in 2002 has experienced a second bout of the same problem.

In 2002, the plant, Davis-Besse, in Oak Harbor, Ohio, developed leaks in parts on the vessel head, allowing cooling water from inside the vessel, at 2,200 pounds per square inch of pressure, to leak out. ...

The company assumed it had solved the problem. But recently the new vessel head showed the same leakage pattern."

Matthew L. Wald reports for the New York Times June 7, 2010. [2]