A reactor at the Calvert Cliffs nuclear plant remained shut down this morning as officials assess the damage caused when a piece of debris tossed by heavy winds damaged a transformer. A spokesman said as of 8 a.m. this morning that “Unit 1 is safely off-line.”

A second reactor was working fine at 100 percent power, said Mark Sullivan, the spokesman for the Constellation Energy Nuclear Group. “All employees are safe,” he added.

Sullivan said Saturday night that officials believe the damage was caused by a large piece of aluminum that was torn loose from a building. The “unusual event,” declared by for the plant's Unit 1 is the least serious of four emergency classifications by the Nuclear Regulatory Commission.

The company has begun its response to what it describes as a low-level emergency, and says the plant remains stable. There is no threat to employees or neighbors, according to a statement released by communications director Mark Sullivan.