A tiered composite risk-informed LBB case has been developed for the postulated cracking of outlet feeder dissimilar metal welds. The deterministic LBB assessment shows that 90% of the DMWs at risk satisfy the five mandatory requirements: factor on load, factor on crack length, factor on leak rate, time from detectable leakage to rupture, and factor on consequential leakage. For the remaining 10% of the DMWs at risk have an insufficient factor on leak rate, the AFEA flaw evaluation demonstrates there are at least 58 days available for operator action to shut down the reactor. The probabilistic LBB assessment concludes that the 95~(th) percentile of rupture probability from a single DMW is 5.95 ×10~(-8) and that even 100% inspection every outage (-2.5 EFPY) does not significantly reduce the rupture probability. Of the input parameters for the probabilistic LBB assessment, the operational leak detection limit has the most significant impact on the rupture probability and the influence of WRS is important.
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