12/07/02

A year after the Nuclear Regulatory Commission's controversial decision to let the Davis-Besse nuclear plant continue to run despite concern the reactor lid was leaking, the agency has formally explained its reasoning.

The rationale is outlined in a 10-page document released this week. NRC officials have explained their thinking several times in public meetings, saying that based on the information they had last November, they believed that the risk of postponing an inspection shutdown from Dec. 31, 2001, until Feb. 16, 2002, was acceptably small. But nuclear safety activists, a member of Congress and members of their own agency have criticized the regulators for failing to put the explanation in writing.

The activists want the NRC narrative - which they consider a retroactive attempt to justify a bad decision - to be part of the official record of the Davis-Besse affair, the nation's closest brush with a major nuclear accident since Three Mile Island in 1979.

When the delayed inspection at Davis-Besse finally took place - with NRC sanction - workers found stress cracks in five of the metal nozzles on the lid that allow the reactor's control rods to move in and out of the core.

The cracks on three nozzles were deep enough to enable the reactor's corrosive coolant to seep onto the lid. While replacing one of the nozzles in March, workers were shocked to find the corrosive coolant had, during several years, bored a pineapple-size hole through the thick steel lid, posing danger of a catastrophe.

In hindsight, the NRC decision to allow the inspection postponement seems rash to some agency critics. But taken in the context of what NRC staffers did and didn't know last fall - they suspected but couldn't prove that nozzles were leaking and had no inkling of the rust hole - there was not much risk that any of the nozzles would give way during the several-week inspection postponement, the report says.

"Our knowledge of the crack growth rate and the information that [Davis-Besse officials] provided about the condition of the head [lid] all led us to believe that [the risk from] allowing the plant to operate to Feb. 16 was acceptably low," said Brian Sheron, the agency's associate director for licensing. "There's a lot of information coming to light that we didn't have available to us" last fall.

The NRC's criminal unit is investigating whether Davis-Besse's owner, FirstEnergy Corp., intentionally withheld evidence that the reactor's lid was corroding.

Although the NRC's report contends that mathematical calculations of an accident risk at Davis-Besse were small during the short inspection postponement, a nationally known nuclear safety engineer says the agency didn't follow its own guidelines for making decisions using such risk numbers.

Only one of the five guidelines were met, said the Union of Concerned Scientists' David Lochbaum. "I understand they're not the Ten Commandments, but they are factors that are supposed to shape a regulatory decision. Shouldn't that give one pause?"

Sheron said that, "in principle, we felt most if not all [of the guidelines] were met in the short term." And FirstEnergy agreed to extra actions to lessen the risk of compounding a nozzle-failure accident, such as extra training for reactor operators and designating a worker to oversee that the reactor coolant kept flowing in an emergency.

Some NRC staffers questioned the value of those measures, but Sheron said the staff ultimately agreed that the danger from Davis-Besse operating an additional eight weeks was minimal.

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