Reliability analysis of the JET neutral injection beamlines

Early operation of the JET (Joint European Torus) neutral injection systems was affected adversely by poor reliability in some of the duct protection, electrodeposited components, and inconel bellows. A quantitative reliability analysis has been undertaken to highlight necessary design and component improvements. The analysis is based on a two-stage Markov model followed by a Duane model of the system. The Markov model represents the system as having two stages: working and failure stages. Expressions for reliability and availability are obtained in terms of failure and repair rates, which do not change radically for relatively large periods of time. The Duane model is a curve-fitting model for the time evolution of fault occurrences. It can quantify any reliability improvements and predict future failure rates at a certain level of confidence. The model has shown that a series of design and component changes has resulted in manyfold increase in the reliability of the system. Copper electrode-position has been largely replaced by contact cooling or deep-drilling technology. The number of bellows is being minimized and their manufacturing methods are being improved. An upgraded duct protection system is being implemented