Common cause failure experience for reliability analysis and design guidelines in large nuclear breeder plants

Failure experience in all PWR auxiliary feedwater systems (AFWS) was reviewed for calendar 1975. Common cause failures (CCF) were examined in detail. An identification/classification scheme was developed for CCF's. Common mode failures were regarded as a special sub-class of CCF. The PWR experience indicated that about one out of four failures in the AFWS was a CCF. Most of the CCF's did not cause a significant loss of availability of the AFWS. System failures dominated the CCF's while hardware failures dominated non-CCF's. Design inadequacies were the most frequent cause of CCF's. A strong systems integration effort in the design stage of large breeder reactors is recommended to help avoid CCF's. A number of CCF's involved the failure to assure the required supply of condensate water to the AFWS pumps according to technical specifications. Increased design attention to this part of the AFWS is recommended for large breeder plants. Numerous other recommendations are included