ICONE15-10504 A REALISTIC APPROACH TO THE ANALYSIS OF LOSS OF OFFSITE POWER EVENTS AT NUCLEAR POWER PLANTS

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The current methods used in the U.S. PRAs to calculate the loss of offsite power (LOOP) initiating event frequency and offsite power non-recovery probability do not adequately account for the plant-specific considerations for estimating these parameters. This is inconsistent with the ASME standard requirements for internal events PRA for risk-significant model elements. This paper presents a realistic approach to the analysis of the LOOP initiating event frequency and offsite power non-recovery probability. The U.S. industry LOOP events are collected and reviewed for applicability to the specific plant being analyzed. The initial random failures in the chain of events that eventually lead to the LOOP at other U.S. plants are combined with the switchyard design and operations of the specific plant being analyzed to determine if the same or equivalent failures would result in a LOOP event. Only those applicable events are then used for the analysis of the LOOP initiating event frequency. Similarly, the industry generic LOOP events are screened to determine if the recovery duration in the generic event is applicable to the plant being analyzed. Generic restoration duration may sometimes be adjusted for use under the emergency conditions. It is believed that the use of this plant-specific approach to refine and process the raw, LOOP events would produce much more realistic LOOP event estimates and more accurate PRA results.