The surge line elbow weld was analysed at a 60-year life assuming the same cyclic conditions as for the elbow itself, but with the stresses factored down by 20 percent as suggested at the Elicitation Base Case Review Meeting on June 4 and 5, 2003 in Bethesda, Maryland. The two hydro cases were, however, maintained at their original values.

In this analysis, RR-PRODIGAL first simulates the weld construction, including any build inspections, to establish the start of life defect density and distribution for both buried and surface breaking defects. As stated earlier, conditional failure probabilities are assessed for both situations and combined to give the final failure probability.

The failure probability evaluated for this case was:

Table G.3 Results for PWR Surge Line Weld Analysis

It can be seen that this failure probability is over an order of magnitude higher than the base case.

This is due to the difference between having to initiate a defect and then grow this defect to failure, and having the probability of pre-existing defects in the weld. The base case values from the base material failure as reflected in Table G.2, i. e. crack initiation leading to failure, have been used in Table D. 1 in the main body of this report. Note, however, that the values reported in Table G.2 are cumulative probabilities of failure in 25, 40, and 60 years whereas the values reported in Table D.1 of the main body are frequencies. Consequently, the Table G.2 values need to be divided by 25, 40, and 60 years, respectively to facilitate any comparisons. Furthermore, the values in Table D.1 are for leak rates greater than the threshold leak rates, i. e., 380 lpm (100 gpm) while the values in Table G.2 reflect the totals.