Abstract
The analytical/deterministic modelling and simulation/probabilistic methods are used separately as a rule in order to analyse the physical processes and random or uncertain events. However, in the currently used probabilistic safety assessment this is an issue. The lack of treatment of dynamic interactions between the physical processes on one hand and random events on the other hand causes the limited assessment. In general, there are a lot of mathematical modelling theories, which can be used separately or integrated in order to extend possibilities of modelling and analysis. The Theory of Probabilistic Dynamics (TPD) and its augmented version based on the concept of stimulus and delay are introduced for the dynamic reliability modelling and the simulation of accidents in hybrid (continuous-discrete) systems considering uncertain events. An approach of non-Markovian simulation and uncertainty analysis is discussed in order to adapt the Stimulus-Driven TPD for practical applications. The developed approach and related methods are used as a basis for a test case simulation in view of various methods applications for severe accident scenario simulation and uncertainty analysis. For this and for wider analysis of accident sequences the initial test case specification is then extended and discussed. Finally, it is concluded that enhancing the modelling of stimulated dynamics with uncertainty and sensitivity analysis allows the detailed simulation of complex system characteristics and representation of their uncertainty. The developed approach of accident modelling and analysis can be efficiently used to estimate the reliability of hybrid systems and at the same time to analyze and possibly decrease the uncertainty of this estimate.
Highlights
A number of different methodologies were proposed in order to analyze stochastic events and the time intervals that elapse between them
The used USS interacts with DSS and performs an additional statistical analysis; that is, outputs from DSS are transferred to the USS system, which perform an integrated uncertainty and sensitivity analysis
The physical model was based on various deterministic laws and process variables and combustion phenomena modelling, all together combined with simulation of various stimuli and corresponding delays, dynamics and random events related to the Passive Autocatalytic Recombiners (PAR), Safety Injection System (SIS), and Containment Heat Removal System (CHRS) [26]
Summary
A number of different methodologies were proposed in order to analyze stochastic events and the time intervals that elapse between them. The main contribution of this paper to the reliability assessment field is in wider discussion of stimulus-driven treatment of probabilistic dynamics and in practical application of related methods and development of approach for severe accident scenario simulation and uncertainty analysis, which was demonstrated by the test case and extension of its initial specification. This can be further used in the benchmark exercise for comparison of other methods and approaches. By discussions and conclusions, the paper is completed summarizing the related PSA issues and advantages of proposed approach application for accident sequence analysis considering hybrid systems and uncertain events
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