US nuclear regulators have scolded FirstEnergy Corp. for failing to recognise as early as 1999 that dirty air filters covered with rust and boric acid indicated a serious problem near the company’s reactor in Ohio. The unexpected discovery in March of corrosion in a massive 17-foot piece of carbon steel bolted on top of the plant’s reactor has alarmed regulators. The corrosion in the steel plate, known as a reactor head vessel, was so severe that the acid had eaten nearly all the way through the 6-inch (15-cm) thick vessel head. If the slender strip of steel remaining atop the reactor had been penetrated, it would have caused a “radiological mess within the containment area,” Dyer said. Although not a direct threat to public health, radioactive steam would have filled the cement containment building, breaching one of three key safeguards surrounding the reactor, he said.
