Operators of the Calvert Cliffs nuclear power plant in Southern Maryland have shut down one of the two reactors there because a control rod unexpectedly dropped into the reactor core, causing a reduction in power generation, a plant spokesman said Monday.
The incident happened Sunday afternoon, prompting the plant's staff to shut the reactor down to find and fix the cause of the malfunction, according to Kory Raftery, spokesman for Constellation Energy Nuclear Group. Control rods are used in a reactor to limit the fission taking place among the reactor's enriched-uranium fuel rods.
An unplanned insertion of a control rod into a reactor core can "create an imbalance in the fissioning and pose challenges for reactor operators," according to Neil Sheehan, a spokesman for the Nuclear Regulatory Commission. He described it as an infrequent occurrence among U.S. nuclear plants.