Availability and Reliability Assessment for ITER Radial X-Ray Camera System in Final Design

Abstract

ITER is an international experimental nuclear fusion device. In the project, the RAMI approach (reliability, availability, maintainability, and inspectability) has been adopted for technical risk control to mitigate all the possible failures of components in preparation for operation and maintenance. The availability and reliability assessment is required and is one of main design contents in the ITER radial X-ray camera diagnostic (RXC) system final design review phase. The availability and reliability assessment, based on the RAMI program, ensured the system with a very high performance to measure the X-ray emission and research the MHD of plasma with high accuracy on the ITER machine. A functional breakdown was prepared in a bottom-up approach, and the system was divided into three main functions, eight intermediate functions, and 31 basic functions which are described using the IDEFØ method. Reliability block diagrams (RBDs) were prepared to calculate the reliability and availability of each function under assumption of operation conditions and failure data. Initial and expected scenarios were analyzed to define risk-mitigation actions. The initial availability of RXC system was 86.13%, while after optimizations were taken the expected availability was 92.57%. The initial reliability for all functions of ITER RXC system was 92.3% without spares and 94.7% with spares over 16 months. A failure modes, effects, and criticality analysis (FMECA) was performed to the system initial risk. Criticality charts highlight the risks of the different failure modes with regard to the probability of their occurrence and impact on operations. There are 29 risks for the initial state, including 16 major risks. No major risk remains after taking into account all the actions. It was assessed that the RAMI analysis results meet the project requirement in the final design phase and the results will be qualified further with the system manufacture going ahead.