Load and resistance factor design approach for seismic buckling of fast reactor vessels

Abstract

Seismic buckling of vessels is one of the main concerns for the design of nuclear power plants in Japan. Rational design is important, especially for fast reactor plants. Although thicker walls are preferable in terms of prevention of seismic buckling, excessively thick walls cause unacceptable creep-fatigue interaction damage. In a previous study, we proposed an evaluation method for the seismic buckling probability of a reactor vessel considering seismic hazards and showed that among the random variables considered in the evaluation, seismic load had the most significant impact on buckling probability. This suggests that more rational vessel designs can be realized by taking appropriate account of seismic load variations. The load and resistance factor design (LRFD) method enables us to determine design factors corresponding to target reliability by considering the variations of random variables. Therefore, in this study, we used the LRFD method to develop a new design rule for the prevention of seismic buckling of vessels. The equation in the proposed rule is almost the same as that in the Japan Society of Mechanical Engineers fast reactor codes, but every random variable, seismic load and yield stress, has its own design factor. In addition, mean or median values are used in the evaluation instead of design values including conservativeness. The effectiveness of the new design rule was illustrated in comparison with the current provision.