The plant, Davis-Besse, near Toledo, has since undergone extensive changes in hardware and personnel, although critics say the reopening is premature. Some are hoping that the owner, the FirstEnergy Corporation, will sell the plant to another operator.
The shutdown is the longest in recent years among the nation's 103 operable reactors, and the discovery raised questions about the industry's ability to learn from its mistakes, since corrosion by such acid was a known problem and First Energy failed to inspect for it.
Avoiding accidents by recognizing problems in their early stages is a critical lesson of the Three Mile Island accident, which occurred 25 years ago this month near Harrisburg, Pa. Despite that accident, which involved a partial meltdown, officials were chagrined to discover that a similar event had almost occurred at Davis-Besse, which is of the same design. But knowledge of the reactor's vulnerability had not been communicated to other operators of the same model.
The corrosion incident also exposed problems within the staff of the regulatory commission, which initially wanted prompt inspections of all 68 plants that could be vulnerable to the problem but relented and gave the owners permission to delay, leaving time for the hole in the lid to grow. Plants are designed with emergency equipment to cope with leaks, but the designs do not contemplate failure of the steel in that location, which is 6 inches thick.
A subsequent investigation by the commission's inspector general found poor communications within the agency itself. The commission had a photo taken during a refueling shutdown in 2000 that showed evidence of the corrosion, but officials failed to act on it, according to the inspector general. The commission staff said that it was still in the process of reforming its internal procedures.
Recently, the commission staff said that it had grounds for "reasonable assurance" that the Davis-Besse plant, in Oak Harbor, Ohio, could be started up and operated safely, but that the commission would maintain extra scrutiny of the plant for five years.
A major part of the changes at the plant, the commission staff said, was changes in its "safety culture," or the willingness of plant workers to raise safety questions to managers, and their expectation that such questions would be properly resolved.
FirstEnergy has acknowledged that it delayed an inspection because that would have forced the closing of the reactor and a loss in electricity production, and that it was insufficiently curious about other indications of trouble, like the presence of the acid, in powdered form, around the reactor building.
James Caldwell, the regional administrator for the commission's Midwest region, said that safety culture was still a problem the first time that his agency considered allowing the plant to restart, but that recently "our folks interviewed about 120 people, and based on that interview, we determined that the folks said they would raise safety issue, and management would deal with safety issues promptly."
In anticipation of the announcement, FirstEnergy heated up the reactor to more than 500 degrees Farenheit and to more than 2,000 pounds per square inch of pressure. It will be back to full power in 10 to 14 days, a spokesman, Todd Schneider, said. FirstEnergy has spent more than $600 million on replacement power and on physical improvements at the reactor, he said.
The company still faces a criminal investigation by a federal grand jury into its handling of the corrosion matter. Paul Blanch, an electrical engineer and specialist in what the nuclear industry calls a "safety-conscious work environment," pointed out that the commission had at one point promised not to allow a restarting of the plant before the criminal issues were resolved, but was now doing so.
"If there are people there that could possibly be indicted, obviously they should not restart," he said.
But a commission spokesman, Jan Strasma, said that although a criminal investigation was continuing, "we see no immediate safety issues that warrant agency action."
Mr. Blanch said that last year he had tried to obtain a copy of the plan that the commission was requiring for reform of Davis-Besse's safety culture, and was turned down, making it difficult for knowledgeable outsiders to determine if the remedy was sound. The commission gave him a copy on reecently, after the announcement, he said. Reopening Davis-Besse is good news for FirstEnergy, but the company faces a variety of other challenges, including the possibility of damage suits arising from the blackout last Aug. 14, which began in its territory and stretched into eight states and parts of Ontario.