By Cat Lazaroff

OAK HARBOR, Ohio, April 8, 2002 (ENS) - The corrosion that drilled a hole in the cap over the nuclear reactor at the Davis-Besse nuclear power plant began as early as 1998, and should have been discovered by utility staff much sooner, government regulators have concluded. A stainless steel plate less than an inch thick is all that remains between the reactor and the inside of the containment building.

The reactor head, seen here from underneath during a maintenance shutdown, is pierced by control rods that can slow or shutdown the reactor. (All photos courtesy NRC)

The Nuclear Regulatory Commission (NRC), the agency that oversees the nation's nuclear materials, says the utility should have found the problem much earlier, perhaps as much as four years ago.

During a public meeting Friday, the NRC detailed the findings of the special inspection team that it sent to the plant in February, after FirstEnergy found the damage while refueling the reactor.

"The team found that evidence of the corrosion damage was present at least as early as 1998 and that the utility missed several opportunities to identify the problem prior to the current refueling outage," the NRC reported.

"This problem would have been prevented," if the utility had followed safety regulations regarding plant monitoring and maintenance, said John Grobe, director of NRC's reactor safety division.

According to the NRC, staff at the Davis-Besse plant noticed in 1999 that they had to change the filters on a radiation monitor with increasing frequency, moving from once a month changes to swapping filters every other day.

An overview of the reactor, with workers standing on top of the reactor vessel head.

These issues should have signaled the presence of a leak somewhere in the system, and prompted the utility to locate and fix the problem, the NRC concluded.

The utility also failed to implement a boric acid control program required by the NRC that would have uncovered the damaged reactor head much earlier, the agency said. Though the utility had been cleaning boric acid deposits out of the reactor cooling system and radiation filters, it left growing deposits on the reactor containment vessel itself.

During the 2000 maintenance at the plant, the utility noticed that the boric acid deposits had changed color, from a light white or yellow to a rust tinted brown. That should have been a red flag, the NRC says, informing the utility that metal somewhere was being corroded.

Still, FirstEnergy let the deposits on the reactor vessel grow.

So much boric acid had been deposited on the reactor vessel lid by February 2002 that it had to be pried off with crowbars before the utility's crew uncovered the six inch hole in the steel vessel. Two weeks later, the team found another, smaller hole, measuring about 1 3/4 inch deep.

"Boric acid deposits were not properly removed and indications of reactor vessel head corrosion were not recognized or evaluated," the NRC report states. "In the 2000 refueling outage significant deposits of boric acid - different in color and consistency previously associated with reactor cooling system leaks - were found on the reactor vessel head."

The leak from the coolant system also left boric acid deposits on water pipes, stairwells, and other areas of the containment building, the NRC said.

The Davis-Besse nuclear power plant is located about 25 miles east of Toledo, Ohio.

"We are clearly responsible for this condition of the reactor head," said Robert Saunders, president of FirstEnergy's nuclear division.

Many of the 300 or so members of the public who attended Friday's meeting answered Saunders with cries of "Shut it down!" and "You failed!"

While the NRC is continuing to investigate the cause of the leak, the agency has called on all nuclear power plants with similar cooling systems to look for boric acid deposits that might indicate a leak and possible corrosion damage. Operators of all 69 U.S. pressurized water nuclear power reactors were notified in March to look for damage to their reactor vessels, but not specifically for boric acid deposits.

So far, no similar corrosion damage has been found at other nuclear plants.

If the reactor vessel had been breached by the acid, the NRC and FirstEnergy said that any radiation released would have been contained within the reactor building, and would not have been released into the environment. The release would have created a "radiological mess" within the reactor building, but would not have endangered the public, the NRC said.