Uncertainties associated with the reliability of thermal-hydraulic nuclear passive systems

ABSTRACT

The increasing adoption of passive safety based front-line systems in advanced nuclear power reactors due to their simplicity, cost competitiveness and autonomous nature makes it very essential to carefully consider the uncertainties associated with their behaviour and the phenomena linked to their operations. The passive safety systems (PSSs) are known to be characterized with several uncertainties in their modelling and operations. These uncertainties are usually more pronounced than those of their active systems counterparts due to the stochastic nature of the associated phenomena, insufficient knowledge of their physics of operation and inadequacy of relevant real/experimental data. This paper thus focused on the uncertainty issues of the thermal-hydraulic (t-h) PSSs which influence their reliability analysis. In addition, the inadequacies of previous research, current research challenges and likely future research directions on uncertainties associated with the models and phenomena applicable to the t-h PSSs adopted in advanced reactors were discussed. For the purpose of illustration, Weibull distribution was adopted for the failures associated with a generic passively cooled steam generator and Bayesian approach applied to account for phenomenological uncertainty. The output of the approach justified the need to account for epistemic uncertainty in reliability analysis of such systems.