A Reliability Estimation Method for Dynamic Systems Which have Various Operation Modes Varying with Time

Abstract

The safety of nuclear power plants is analyzed by a probabilistic risk assessment and fault tree analysis is the most widely used method for the risk assessment with event tree analysis. For the reliability analysis of dynamic systems which have various system states as a function of time, dynamic fault tree methods have been developed based on the conventional static fault trees. The fault tree provides meaningful data for the evaluation and improvement of the overall reliability of the target systems. One disadvantage of the fault tree is that the modeling of fault tree requires experts with extensive knowledge of the system, since modeling a fault tree for a complex system is a very cumbersome task. Several graphical modeling methods have been proposed for the convenient and intuitive modeling of complex systems, but they have difficulty in the reliability analysis of dynamic systems. In this paper, the reliability graph with general gates (RGGG) method, an intuitive modeling method based on Bayesian networks, is improved for the reliability and availability analyses of complex dynamic systems which have various operation modes varying with time. A novel concept of a reliability matrix is proposed with an explanation of how to utilize the reliability matrix in the RGGG for the various cases of system configuration changes. The proposed RGGG with a reliability matrix provides convenient and intuitive modeling of various operation modes of complex systems and it has wide applicability to various failure mechanisms compared to the fault tree methods.