The Nuclear Regulatory Commission has determined that incorrect calculations made as long as 12 years ago at the nuclear power plant near Richland could have led to a delay in recognizing a potentially serious emergency.
The issue was discovered and fixed in December and January by Energy Northwest, which operates the Columbia Generating Station.
The NRC, which ranks inspections findings on a color-code system, has given its findings a preliminary classification of "white" for low to moderate safety significance. Inspection findings are not unusual, but most are classified as "green" for very low safety significance.
NRC will issue its final determination of safety significance in 90 days after discussions with Energy Northwest officials.
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If the safety significance is white, NRC could increase oversight of the nuclear power reactor. A return inspection will be made based on the findings, said Mike Paoli, Energy Northwest spokesman.
NRC notified Energy Northwest of two preliminary white findings in a letter Thursday, but also said in an attached report that "the performance deficiencies were not reflective of current licensee performance."
Mark Reddemann became chief executive of Energy Northwest in 2010 and has hired several new executives to work with him.
The issues date back to April 2000, when the effluent monitor of the reactor building stack was improperly calibrated. The radiation source was not positioned in the correct place, leading a technician to inappropriately conclude the detector gas calibration factor had changed from a value of 34.9 to 413.29, according to the NRC.
The significant change was not questioned and the new value was provided to emergency preparedness staff for use in an assessment model of offsite radiation.
The error, which was compounded with related errors over time, led the Quick Emergency Dose Projection System to include values that would have overestimated or underestimated the potential radiation offsite in an emergency, according to the NRC.
The inaccurate data would have caused a delay by Columbia Generating Station in recognizing an emergency requiring precautionary actions to protect the public or a more serious emergency with conditions that threatened the public, according to the report.
However, other systems and checks in place still would have resulted in an emergency being declared, the NRC said.
The NRC made two findings, one for the potential to incorrectly classify the seriousness of an emergency and the other for the potential for wrong actions to be taken in response.