As outlined above, this LOCA frequency assessment is limited to specific portions of BWR and PWR Code Class 1 piping. The BWR base cases include contributions from potential pipe breaks in Loop B of the respective RR and FW System. Pipe break frequency contributions from normally pressurized sections of HPCI, RCIS, RHR or RWCU piping are not considered in this study. Piping system design information beyond that itemized above is not accounted for in this study. The PWR base cases include contributions from 3-of-3 RC hot legs and 2-of-2 HPI/NMU lines, respectively.

Excluded from the analysis are LOCA frequency contributions due to degradation and failure of cast stainless steel components such as valve bodies. While there is some documented evidence of degradation of such components, (e. g., [D.10]) the frequency of a through-wall defect in valve bodies and pump casings is viewed as being considerably lower than for welds in Class 1 systems.