As summarized in Section D.3.3, there have been only a few through-wall defects in Class 1 PWR piping. For the RC-HL, the rate of PWSCC per weld-year is established using the normalization process discussed in Section D.4.2.1 and with the following specializations:

RC-HL Apriori Failure Rate

• The apriori failure rate is derived using the PIPExp for the time-period 1970 through 2000 to include the consideration of the through-wall defect at V. C. Summer.

• Table D.8 includes the weld population data used to calculate ^NPS3o = 8.12E-05 per weld-year.

• Failure rate “post-processing” to account for different weld configuration susceptibilities to PWSCC is done consistent with Section D.4.2 and with the S and Aj assumed values shown in Table D.9.

In contrast to the BWR weld susceptibility factors in Table D.5, the weld susceptibility factors in Table D.10 are assumed values that reflect the applicable service experience. As an example, for the RC Hot Leg the nozzle-to-safe-end weld is assigned the highest value in view of the available service experience; i. e., the Ringhals and V. C. Summer hot leg cracking as described in Section D.3.3.1. As another example, for the RC Surge Line, relatively high weld susceptibility factors are assigned the safe-end welds and Hot Leg branch connection. In view of the recent experience at TMI-1, the nozzle-to-safe-end weld is given a greater weight than other weld configurations. The uncertainty in the PWR weld susceptibility factors is not evaluated

further in this study, however. EPRI TR-111880[10] is used for characterizing the prior knowledge about pipe failure due to thermal fatigue.