Seismic capacity evaluation of a group of vertical U-tube heat exchanger with support frames for seismic PSA

Watanabe, Yuichi*; Muramatsu, Ken; Oikawa, Tetsukuni

This paper presents an evaluation of seismic capacity of a group of vertical U-tube type heat exchangers(HXs) with support frames for residual heat removal systems of BWRs for seismic Probabilistic Safety Assessment in Japan. The median capacity was evaluated by a time history response analysis with a detailed model for a representative HX selected from four HXs. The logarithmic standard deviation(LSD) for uncertainty due to lack of knowledge was evaluated with consideration of the variabilities in three influential parameters, i.e., diameter of anchor bolt, weight of HX and position of center of gravity of HX. The dominant failure mode of HXs was the failure of anchor bolts of lugs mainly due to shearing stress. The capacity expressed in terms of zero period acceleration on the foundation of HX was evaluated to be 4,180 Gal(4.3 g) for median, LSD for uncertainty due to randomness was 0.11 from the variability in material property and LSD due to lack of knowledge was 0.21 to 0.53 depending on combination of the variability in design parameters to be considered.