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Calvert Cliffs Nuclear Power Plant Unit 2 could come under increased scrutiny by the U.S. Nuclear Regulatory Commission with an increased “white” rating for low to moderate safety significance.

The NRC has given a preliminary white finding, an increase from the lowest safety significance finding of green. A white rating may require additional inspections, regulatory actions and oversight according to an Aug. 8 letter from the NRC to the Calvert Cliffs site vice president.

Calvert Cliffs Nuclear Power Plant has 10 days from the date of the letter to make a decision on how to respond. The choices are to request a regulatory conference, to submit written comments or to accept the finding.

Kory Raftery, plant spokesman, said a decision on the next steps has not yet been made.

“At this point, we’re still evaluating,” Raftery said Monday.

The plant was given this preliminary finding because in October 2013 Exelon replaced the main steam line radiation monitors and changed the threshold values for emergency levels, according to the Aug. 8 letter. The four levels are an unusual event, an alert, a site area emergency and a general emergency, NRC spokesman Neil Sheehan said Monday.

“This error could have resulted in an over-classification on an event, an unnecessary protective action recommendation, and caused offsite response organizations to implement unnecessary protective actions for the public,” according to the Aug. 8 letter.

Exelon, the company that owns the plant, identified this error, and no events were over-classified between the time of the threshold error in October and the discovery of the error in April, Raftery said.

The NRC will make a final determination within 90 days, according to the Aug. 8 letter.

“If this is finalized as a white … it means they would get additional oversight from the NRC,” Sheehan said.

The white finding could only be temporary depending on the results of a thorough root cause investigation, Sheehan said. An additional team of inspectors will be sent to make sure no other parts of operations were affected by the oversight.

Previously, Unit 2 was issued a white inspection finding in 2010 for a failure to implement scheduled preventative maintenance on safety-related delay relays used in the operation of one of the plant’s emergency diesel generators. The finding was closed after a supplemental inspection in March 2011. Additionally, both units received a finding greater than green in a security-related inspection in 2011 and returned to a green rating in 2012, Sheehan said.