OAK HARBOR, Ohio?Acid leaking from a nuclear plant ate a 6-inch hole in a steel cap that covers the plant’s reactor, federal inspectors said.

The regulatory commission has alerted the nation’s 102 other commercial nuclear plants to watch for similar problems. It said this was the most extensive corrosion ever found on top of a U.S. nuclear plant reactor.

Trace amounts of boric acid, which the plant’s reactor creates during the nuclear fission process, are believed to have dribbled from at least one of 69 control rods nozzles.

The corrosion problem will keep the plant closed an extra month, officials said. The plant, about 25 miles east of Toledo, will be shut down until at least late April. The plant plans to install a new reactor head during the plant’s next refueling in 2004.

Nuclear Regulatory Commission spokesman Jan Strasma said the hole does not pose a safety threat.