Public Affairs Officer
We regularly interact with various audiences from the media to the public and one question pops up often: Why does the NRC use colors to discuss issues found at a plant and what does it all mean?
The quick answer is that color-coding is a lot more understandable to people outside the agency than trying to interpret a probabilistic risk calculation of core damage frequency of 10-5. (The NRC uses probabilistic risk in assessing the potential safety significance of nuclear safety issues and plant performance indicators so inspections focus on those plant activities that could have the greatest impact on safety.)
The colors we use — green, white, yellow and red — are used to prioritize the findings with greater safety significance. A more risk-significant issue is called a red finding and that will move an operating plant into our highest category for oversight followed by thousands of extra hours of inspection. An example would be a failure in a key safety-related component.
A green finding might be given when an inspector finds that one of 10 bolts on a valve is looser than the others and should be tightened. While it may not sound like a big deal, the NRC has high standards for safety and a low threshold for issues.
White and yellow findings are medium risk. In 2015, 428 green findings, 13 white findings and two yellow findings were issued. An example of a yellow finding was one given for seals that were not adequate to protect a room housing electrical equipment from flooding. An example of a white finding was for improper maintenance that resulted in a failed emergency diesel generator fan belt.
Who decides the colors? Initially, the inspector determines the safety significance and assigns a tentative color. A green finding may not require additional analysis. But with the higher colors, there is a detailed assessment that could involve NRC risk experts and, in some cases, a discussion with the plant operator to obtain more information.
The final outcome of the review — evaluating whether the finding is green, white, yellow, or red — will be used to determine what further NRC action may be called for, such as moving a plant up in the columns that comprise the NRC’s performance “Action Matrix.” When poor performance lands a plant in one of these higher oversight columns with increased inspections, it takes a lot of hard work to return the plant to a better standing.