Limiter probabilistic lifetime analysis

Reliability of tokamak fusion reactors is a key parameter in the successful development of commercial fusion power. In addition, reliability analysis can be used during the design phase of reactor development to perform tradeoff studies. Generation of a set of reliability curves for a particular tokamak in-vessel component, the limiter, is the focus of this paper.The methodology implemented to generate the set of reliability curves consists of the following steps:(1)Identifying those particulars deemed important in characterizing normal and transient operation. This includes enumeration of events initiating transients, referred to as Initiating Events (IE's), via facility level fault tree analysis, of the transients considered.(2)Specifying Failure Modes (FM's) and associated Failure Criteria (FC) to be included in the analysis. Previous lifetime studies, existing design codes and engineering judgment used as guidelines in choosing relevant FM's and FC.(3)Developing and integrating models for normal operation, transient operation and FM's to assess failure times.(4)Assessing probability distributions for state-of-knowledge uncertainties surrounding models and key parameters. These uncertainties are then propagated through a statistical lifetime model to obtain a probabilistic description of limiter reliability. The impact of various parameters on limiter reliability is examined.Results show that the limiter reliability decreases rapidly as a function of time. The occurrence of transients is the main contributor to decreased reliability. The dominant FM's are material loss and cumulative cyclic damage.