US regulators have ordered 69 nuclear plants to submit reactor safety information after finding unexpected corrosion at an Ohio plant owned by FirstEnergy Corp. that raised broader concerns. FirstEnergy last month shut its Davis-Besse nuclear power plant in Oak Harbor, Ohio, because of corrosion inside the reactor chamber. The Nuclear Regulatory Commission wrote to 69 US plants with pressurised water reactors similar to Davis-Besse’s seeking information on their structural integrity. The agency said it did not believe the problems at the Ohio plant could release radiation into the atmosphere, but that they could reduce its margin of safety. While refuelling the Ohio plant in February, FirstEnergy found an area on top a high-pressure vessel which contains the nuclear reaction showed unusual wear. Corrosion left less than one-quarter inch of stainless steel to protect the top of the reactor vessel, normally shielded by 6.5 inches of carbon steel, the NRC spokesman said. The NRC said it expects that a corrosive coolant leaking from the reactor core ate through the pressure vessel, but has not announced definite findings. The NRC said it will use the new information to determine if its current inspection and maintenance practices are adequate. NRC inspections now under way at Davis-Besse show boric acid in the cooling water was a contributing cause of corrosion. Boric acid is added to the water to control the speed of the nuclear reaction.