Influence of dead weight and internal pressure to seismic buckling probability of fast reactor vessels

Abstract

Seismic buckling of vessels is one of main concerns for the design of fast reactor plants in Japan. Rational design is important because of two conflicting requirements; thicker walls are preferable to prevent seismic buckling of vessels, while excessively thick walls introduce large thermal stress causing unacceptable creep-fatigue interaction damage. In previous studies, we discussed evaluation methods of seismic buckling probability of vessels by taking account of seismic hazards in order to rationalize seismic buckling evaluation, and proposed a rule for seismic buckling of vessels based on the load and resistant factor design method. The proposed rule is expected to widen design window regarding seismic buckling and contribute to more reasonable design of vessels of fast reactors. However, there is still a room for more rational design. The proposed method deals with only seismic load, but in actuality, dead weight and internal pressure also exist. The existence of these loads contributes to reducing the buckling probability because axial compressive load decreases. In this study, the rule was expanded so that dead weight and internal pressure can be taken into account. Furthermore, the influences of dead weight and internal pressure to seismic buckling evaluation were discussed. As result, it was shown that approximately 10 to 20% of further rationalization of allowable seismic load could be achieved by considering dead weight and internal pressure in the evaluation. In addition, it was found that the previously proposed design rule, not considering dead weight and internal pressure, includes approximately 2 to 10 times margins in terms of seismic buckling probability.