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In February 2002, during a routine inspection at Ohio's Davis-Besse nuclear power station, inspectors found three cracks in the lid of the reactor's pressure vessel, the mighty steel cylinder that encloses the radioactive core. One crack was in the housing of a mechanism that drives control rods into the reactor core to manage the nuclear reaction. The flaws needed to be repaired, but there was no sense of urgency-that is, until workers began fixing the crack in the control rod mechanism and they felt a wiggle. A wiggle that was all wrong.