LOCA Issue development required the group to brainstorm important LOCA issues. The group first defined a structure for categorizing issues in the form of a flowchart (Figure B.1.1). It was stressed that the LOCA frequencies in this exercise will consider only passive system failure. Active system failure will not be considered for the following reasons:

1. The panel has no specific expertise in these types of failures.

2. Failure of these components is not as rare and there is adequate data to assess their contribution to the LOCA frequencies.

3. Active components are subject to ongoing maintenance which should diminish the likelihood of future failure rate increases.

However, LOCA frequency contributions from active components will be combined with the passive component contributions to develop final LOCA estimates which can be supplied as PRA input. The estimation of these contributions will occur separately, but will be summarized for the panel at the wrap — up meeting.

The group divided the passive system LOCA sources (Figure B.1.1) into two classes: piping and non­piping. Non-piping contributions include RPVs, steam generators, bolting flange failures, valves, pumps, etc. The distinction between piping and non-piping categorization is useful because piping has unique issues.