Effect of correlations of component failures and cross-connections of EDGs on seismically induced core damages of a multi-unit site

Muramatsu, Ken; Liu, Q.; Uchiyama, Tomoaki*

Aiming at proposing effective applications of seismic PSA for risk management of nuclear facilities, a preliminary study was conducted for a multi-unit site to examine core damage frequency (CDF) and core damage sequences with consideration of correlation of component failures. Besides, the effectiveness of an accident management measure, namely, cross connection of emergency diesel generators (EDGs) between adjacent units was also examined. Twin BWR-5 units of the same design were hypothesized to be located at the same site and the CDF as well as the accident sequences of this site was analyzed by using SECOM2. The results showed that the calculated CDF depends on the assumptions on component correlations and when the rules for assigning correlation coefficients defined in NUREG-1150 program was adopted, the CDF of a single unit, the CDF of this site and the frequency of simultaneous core damage of both units increased. Further, it might be possible that simultaneous core damage of both units was caused by pairs of different accident sequences. When cross-connection of EDGs between two units was available, the CDF of a single unit, the CDF of this site as well as the frequency of simultaneous core damage of both units decreased, which indicated that cross-connection of EDGs can be an effective measure for reducing seismic risk.