Mean values of distributions should, in general, be used for comparison with goals or criteria, although the sensitivity of the mean value to the high tail of a distribution should not be overlooked. For very broad distributions, such as those that typically result when significant model uncertainty is present, reliance on the mean values may not be appropriate and a more detailed investigation of the reasons for this large uncertainty should be undertaken. This could possibly lead to decisions to conduct additional research or to take other measures. Accounting for uncertainty in the case of plant characteristics or phenomena that are not currently modeled at all is much more difficult. We agree and encourage the staff to actively pursue the resolution of this issue.
Packaging is the process by which risk trade-offs can be accomplished.
It is a significant benefit of risk-informed regulation. We believe that it is the overall impact on plant risk that is important, and related changes should be handled as a package. We will continue to monitor the progress of the staff on these issues. During this review, we had the benefit of discussions with representatives of the staff and of the Westinghouse Electric Corporation. We also had the benefit of the documents referenced.