Development of severe accident evaluation technology (level 2 PSA) for sodium-cooled fast reactors. (2) Identification of dominant factors in initiating phase of unprotected events

As a part of establishing level-2 PSA evaluation method, Initiating Phase of the unprotected loss-of-flow accident was studied with theoretical investigation focusing on reactivity balance during the transient and SAS4A code analysis. Based on the knowledge accumulated in the past and present work, key parameters to be considered in the event-tree quantification were clarified. Through the SAS4A code analysis adopting the JSFR design parameters as the reference, importance of the identified items was confirmed. Within the parametric cases covered in this study, all the cases resulted in non-energetic transients demonstrating that IP energetics is highly unlikely with the JSFR design. (author)