07/03/02

Nuclear Regulatory Commission investigators found numerous instances at which Davis-Besse workers could have identified corrosion that ultimately ate through the reactor lid's 6½ inches of steel. Here are examples:

September 1991 - The exterior of the reactor head was cleaned, and boron deposits were removed. But "the extent of deposits, if any, that remained after cleaning was not documented," the NRC noted in a report in May 2002.

March 1993 - Boric acid deposits were washed off "to the extent possible," the NRC said in the May 2002 report. Patches of brown boric acid deposits were identified. The color (boric acid normally is white) could have indicated the beginning of rust on the reactor head.

April 1996 - At least one boric acid deposit had a brown stain. Plant personnel concluded that only 50 percent to 60 percent of the head had been inspected, apparently because poor accessibility and the head's curved shape made reaching parts of it difficult.

May 1998 - Rust-brown boron deposits were identified near the top center of the head and were removed "as best we can," Davis-Besse personnel reported. They concluded that there was "no impact on vessel head integrity," the NRC reported.

April 2000 - "Lava-like" brown-to-red boric acid deposits more than 1 inch thick were observed on much of the head. Crowbars were needed to remove the "solid rock" deposits. A videotape made after the cleaning shows that a thick layer of "lava-like" deposits remained around nozzles at the center of the head.

Feb. 2002 - Boric acid layer was several inches thick near the center of the head. After removal of the buildup, workers found a 5-by-7-inch corrosion hole in the head.