Japan Atomic Energy Agency has been developing “Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)”, which aims to offer best solution for challenges on the design and operation of a nuclear plant. In a part of ARKADIA for design study including design optimization of components named ARKADIA-Design, we have been developing a process to automatically optimize design parameter of structural components subjected to various kinds of loads, including thermal transient.

In this paper, we propose the simplified procedure to estimate failure probability of components subjected to thermal transient for the design optimization. An objective function of this optimization based on failure probability of the components is assumed, because failure probability can be commonly used as an indicator of component integrity for various failure mechanisms. In order to enable necessary number of the estimations for the design optimization with practical calculation cost, we have aimed to reduce number of analyses required for one estimation. For this purpose, we have adopted the First Order Second Moment (FOSM) method as the estimation method of failure probability on the process of the optimization and an orthogonal table in experiment design method is utilized to define conditions of the analyses for the evaluation of mean and variance of thermal transient stress, which are used as inputs for the FOSM method. The proposed procedure has been applied to the demonstration study to optimize thickness of cylindrical vessel subjected to thermal transient derived from shutdown. We confirmed that the procedure can evaluate the failure probability depending on the cylinder thickness with practical calculation cost.

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