Structural Reliability Assessment for Thermal Fatigue Phenomena in Fast Breeder Reactors Based upon Probabilistic Fracture Mechanics

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1. A mathematical model to analyze thermal striping phenomena in fast breeder reactors is constructed based upon a probabilistic fracture mechanics. By the use of it, a residual life distribution function, as well as a crack length distribution function, is theoretically derived in a closed form. The residual life calculated by the derived distribution is of order of 10^8 cycles when the failure probability of the component is 10^<-5>.2. Sensitivity analysis with respect to model parameters is performed. The result indicates that, if the spectrum of temperature fluctuation is of narrow-band type, the random aspect of thermal fatigue crack growth is mainly affected by the randomness of material's property rather than by the randomness of temperature.3. An approximation method is proposed to express stress interaction effect between cracks by the use of a stress relaxation factor. The method is applied to analyze the case in which the structural component contains many thermal fatigue cracks. The numerical result shows that the mean residual life is shortened as the crack spacing becomes larger.4. It is theoretically clarified that our model is applicable regardless of the shape of the temperature spectrum.