Dependent Failure Quantification

Abstract

Risk reduction almost always would succeed if there were no dependent failures. The dependent failure is a source of a collapse of dependable risk reduction. Some dependencies are modeled explicitly in PRA, while others are dealt with by common-cause failure analysis. This chapter first describes a relatively recent methodology called the alpha-factor model for common-cause quantification. The well-known beta-factor model can be regarded as a variant of the alpha-factor model. The second dependency described in this chapter is a graceful degradation process where changes to inferior states occur in a gradual manner. The graceful or gradual degradation is a key approach to problems with risks because time is available to correct the current inferior situation.