The System Based Code (SBC) concept has been proposed to achieve compatibility in matters of reliability, safety, and cost of Fast Breeder Reactors (FBR). This code extends the present structural design standard to include the areas of load setting, fabrication, inspection, maintenance, and so on. Therefore, a quantitative index which can connect different areas is required. In addition, the determination of its target value is also one of the key points to substantiate the SBC concept. Failure probability is one of the candidate indexes. We have proposed a new method to determine the reliability targets for the structures and components in FBR plants from the safety point of view by utilizing analysis models of a probabilistic safety assessment. In this study, the effectiveness of the failure probability as an index and the compatibility of the reliability targets derived by the new method were investigated through a trial setting of In-Service Inspection (ISI) request on the reactor vessel near the sodium surface based on the SBC concept. The failure probability due to creep-fatigue interaction was calculated by the Monte-Carlo simulation. In response, the reliability targets for fracture related to the risk from internal initiating events were derived. Cumulating the failure probability and the reliability targets up to the end of in-service period enables us to compare them directly, and we obtained a result that the reactor vessel has enough reliability even without ISI. Through this trial, we showed that the failure probability is a promising index, and the reliability targets derived by the new method are compatible with the SBC concept.

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