About Time-Variant Reliability Analysis with Reference to Passive Systems Assessment

This study addresses the time-variant reliability assessment in relation to systems presenting a non-stationary random process during their operation, such as thermal-hydraulic passive systems for advanced reactors, resting on natural circulation. The reliability assessment efforts conducted so far do not address this specific aspect: the dependence upon time is usually ignored, or at most the system unavailability is intended to be assessed per mission time, during which the parameter values, as t-h parameters for instance, are assumed as constant quantities. The study endeavours to present a consistent approach to model the natural circulation passive systems, in terms of time-variant performance parameters, as for instance mass flow-rate and thermal power, to cite any.