The total LOCA frequency is calculated using U. S. NPP experience of zero Category-1 LOCAs (i. e., greater than 380 lpm [100 gpm]) in 2,647 LWR-years of operation (as of 4/24/2003). A Bayesian update of a non-informative prior-distribution was performed to produce a total LOCA frequency of 1.9E-4 per LWR-year.

Table E.1 Total LOCA Frequency (per LWR-Year) Including Uncertainty, Using a Non-
Informative Prior and U. S. LWR Operating Experience

5% 50% mean 95%

7.4E-07 8.6E-05 1.9E-04 7.3E-04

E. 4 LOCA Frequency Allocation by RCS Pipe and Non-Pipe

The total LOCA frequency calculated above is first allocated between pipe and non-pipe passive components using data on primary system leaks and cracks collected from licensee event reports (LERs). These data records were collected, reviewed and categorized specifically for this effort. Since these data will only be used to ascribe a relative frequency between pipe and passive non-pipe components, complete data are not necessary, only data that have been reported consistently. These data and the resultant allocation are summarized in the table below. Steam generator tube ruptures are being assessed separately, and are therefore removed from this allocation.