Analysis of the LaSalle Unit 2 Nuclear Power Plant: Risk Methods Integration and Evaluation Program (RMIEP). Volume 3, Part 2, Internal events accident sequence quantification: Appendices

This volume presents the methodology and results of the internal event accident sequence analysis of the LaSalle Unit II nuclear power plant performed as part of the Level III Probabilistic Risk Assessment being performed by Sandia National Laboratories for the Nuclear Regulatory commission. The total internal core damage frequency has a mean valve of 4.41E-05/R-yr. with a 5th percentile of 2.05E-6/R-yr., a median value of 1.64E-05/R-yr. , and a 95th percentile of 1.39E-04/R-yr. The dominant sequences involve a loss of off-site power (LOSP), immediate or delayed failure of on-site AC power resulting in station-blackout, and failure of the reactor core isolation cooling system (RCIC). The events most important to risk reduction are: frequency of LOSP, non-recovery of offsite power within one hour, diesel generator (DG) cooling water pump common mode failure, and non-recoverable isolation of RCIC during station blackouts. The events most important to risk increase are: failure of various AC power circuit breakers resulting in partial loss of onsite AC power, failure to scram, and DG cooling water common mode failure. The dominant contributors to uncertainty are: control circuit failure rates, relay coil failure to energize, energized relay coils failing deenergized, frequency of LOSP, and DG failure to start.