Development of System Based Code (2) Application of Reliability Target for Configuration of ISI Requirement

Abstract

The concept of System Based Code (SBC) has been proposed to achieve compatibility in matters of reliability, safety, and cost of fast breeder reactors (FBRs). This code extends the present structural design standard to include the broad areas such as load setting, fabrication, inspection, and maintenance related to FBR design and operation. Therefore, a quantitative index that can correlate these different areas is required. One such index is the probability of failure. The determination of a target value is also one of the key points to implement the SBC concept. We have proposed a new method to determine reliability targets for structures and components in FBR plants from the viewpoint of safety. Analysis models based on probabilistic safety assessments are used in the method for determining reliability targets. In this study, the effectiveness of the probability of failure as an index and the reliability targets produced using the new method are investigated through a trial setting of an in-service inspection (ISI) requirement for a reactor vessel. The probability of failure due to fatigue-creep interaction is calculated using a Monte Carlo simulation. The reliability targets for failure related to the risks arising from internal initiating events are derived using the new method. The summation of the probability of failure and of the reliability targets up to the end of the in-service period enables us to compare them directly. The results show that the reactor vessel has sufficient reliability even without an ISI. Through this example, we demonstrate that the probability of failure is a promising index and that reliability targets derived using the new method are compatible with SBC.