The operators of Calvert Cliffs nuclear power plant have been cited for a miscalculation that federal safety inspectors said might have triggered an unnecessary evacuation or other emergency response to an insignificant radiation leak.
The Nuclear Regulatory Commission said Friday it had preliminarily classified the mistake by Exelon Generation Co. as one of "low to moderate" safety significance. But an NRC spokesman said it could lead to increased federal scrutiny of the twin-reactor plant in Lusby, 70 miles south of Baltimore.
The error occurred when Calvert Cliffs replaced radiation detectors last October on the main steam lines for Unit 2, said Neil Sheehan, spokesman for NRC's Region 1 office in King of Prussia, Pa. Plant workers incorrectly set the detectors to trigger an alarm at a radiation level 100 times lower than would be deemed a safety threat, he said.
Plant operators discovered their mistake four months later and fixed it, Sheehan said. But federal regulators are concerned that the improperly set radiation monitors might have prompted plant officials to overreact to a low reading and order an unwarranted emergency response, such as evacuating the plant or residents downwind.
"Ideally, we want them to be in the right zone if they have an emergency event," the NRC spokesman said, "not underclassifying it but not overclassifying it, either."
The company must decide within 30 days whether to accept or challenge the findings of the NRC report. It can do so either by requesting an in-person meeting with federal regulators or by submitting a written rebuttal.
If the NRC does not change its preliminary finding, NRC inspectors would increase oversight of the plant "until we were satisfied the company understood the root causes of the issue and had put in place appropriate corrective actions," Sheehan said.
Kory Raftery, spokesman for the plant, said if the finding stands, Calvert Cliffs likely would undergo a special NRC inspection to ensure that whatever led to the mistake has been corrected. He said the company has incorporated the issue into a "rigorous corrective action program," which is shared with operators of all of Exelon's nuclear plants.
Calvert Cliffs Unit 2 was last cited for a "low to moderate" safety violation in 2010, according to Sheehan, for allegedly failing to perform scheduled maintenance on one of the plant's emergency diesel generators. The generator shut down prematurely as a result during a power failure that year, Sheehan said. The plant also was cited for a less serious, security-related inspection finding in 2011.