Workers at Calvert Cliffs nuclear plant in Southern Maryland were working Sunday afternoon to bring a reactor online after it was shut down late Saturday when a piece of debris tossed by heavy winds from Hurricane Irene damaged a transformer.

Spokesman Mark Sullivan said "Unit 1" remains off-line while workers inspect the transformer and ensure it is in "safe and workable condition."

A second reactor was working fine at 100 percent power, and the plant remains stable, Sullivan said.

Calvert Cliffs officials believe a large piece of aluminum siding struck a transformer, causing Unit 1 to "automatically and safely go off-line, as it is designed to do" about 11 p.m. Saturday.

The incident led officials to announce an "unusual event" for Unit 1, which is the least serious of the four emergency classifications by the Nuclear Regulatory Commission. Just before 8 a.m. Sunday morning, the nuclear plant ended the "unusual event," according to Sullivan.

Sullivan said it's not clear when Unit 1 will resume operations.

"We will do it when it is safe, and we've completed all our emergency checklists," he added. He declined to say what the checklists entail because some are security-related.

hanah.cho@baltsun.com

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