Evaluation Between Existing and Improved CCF Modeling Using the NRC SPAR Models

Abstract: The NRC SPAR models currently employ the alpha factor common cause failure (CCF) methodology and model CCF for a group of redundant components as a single “rolled-up” basic event. These SPAR models will be updated to employ a more computationally intensive and accurate approach by expanding the CCF basic events for all active components to include all terms that appear in the Basic Parameter Model (BPM). A discussion is provided to detail the differences between the rolled-up common cause group (CCG) and expanded BPM adjustment concepts based on differences in core damage frequency and individual component importance measures. Lastly, a hypothetical condition is evaluated with a SPAR model to show the difference in results between the current adjustment method (rolled-up CCF events) and the newer method employing all of the expanded terms in the BPM. The event evaluation on the SPAR model employing the expanded terms will be solved using the graphical evaluation module (GEM) and the proposed method discussed in Reference 1.