Initiating Event Frequency and Mitigation System Unavailability

2 Initiating Event Frequency and Mitigation System Unavailability 

As the Super LWR has never been constructed, it is impossible to prepare the database for PSA. However, taking suitable data from the available PSA database of LWRs helps to roughly estimate the core damage frequency (CDF and to identify the dominant sequences for the CDF. 

The frequencies of the initiating events used for the PSA of the Super LWR are summarized in Table 6.26. Since the reactor vessel is similar to those of PWRs, the frequencies of the LOCAs are taken from PWRs [40]. Since most of the abnormal transients of the Super LWR are taken from those of BWRs as shown in Table 6.4 [1], the frequencies of the three transients are taken from those of BWRs [41]. The unavailabilities of the mitigation systems are also taken from those of LWRs as summarized in Table 6.27. Since the control rods of the Super LWR are inserted from the core top like PWRs, the unavailability of the reactor protection system is taken from PWRs [40]. Since other safety systems, the containment system, and power conversion system are similar to those of BWRs, the unavailabilities of these systems are taken from those of BWRs [41]. 

Mitigation system Unavailability (demand ) References Remark 

RCP AtT-nPCS l.OE-01 At other events l.OE-02 BWR [41] Feedwater system of BWRs 

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