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.