Dive Brief:

• The Nuclear Regulatory Commission will increase its oversight at the Calvert Cliffs Unit 2 nuclear power plant after a report determined internal radiation measurements were improperly calibrated.
• The report classified the error as "white," meaning it has low to moderate safety significance. Exelon agreed there was a problem but said it should have received a lower "green" finding of very-low safety significance.
• The error stemmed from new instrumentation installed in 2013 which was improperly calibrated and which could have led to an emergency being improperly declared.

Dive Insight:

NRC officials say the always expect nuclear plant operators to be vigilant and cautious, but the improper calibration error could have triggered a response when one was actually unwarranted.

In October 2013, the Unit 2 monitors were replaced with new instrumentation that used different units of measurement and required recalculated thresholds for different levels of emergency. During monitor replacements for Unit 1 in March 2014, plant personnel raised questions about the Unit 2 threshold calculations. That led to Exelon, the plant’s owner, determining in April of this year that the Unit 2 Emergency Action Levels were inaccurate and could have led to emergency events being improperly classified.

“Nuclear power plant operators are always expected to err on the side of caution. But this is a  case where an emergency declaration could have been made prematurely, triggering unnecessary responses,” Acting NRC Region I Administrator David Lew said. “While Exelon, to its credit, identified and fixed the incorrect thresholds, it nevertheless allowed their introduction, and they remained in place for about five months.”