Analysis and modelling of software in probabilistic safety assessment

Currently, no consensus approach is available for assessing safety and reliability of digital I&C at nuclear power plants. Due to the absence of a common method for modelling software failures in the probabilistic safety assessment, generic common cause failure probabilities are usually used, which tend to be conservative and may ultimately prevent PSA results from providing proper risk insights. This paper presents a method for the quantification of software failures in a reactor protection system. The emphasis of the method is in the definition of the relevant software fault cases and related failure effects. The outlined quantification method offers a practical and justifiable approach to account for software failures