Specification of a Software Common Cause Analysis Method

Abstract

Electronic safety systems for applications with a high level of safety integrity as in nuclear plants use hardware redundancy extensively. By implementing identical or similar software in the redundant hardware channels, systematic software failures may become a vital origin of common cause failures. The paper specifies a Software Common Cause Analysis allowing a well-documented judgment whether the likelihood of dangerous common cause failures in the conjunction of the system environment with the embedded software is adequately low, or which initiating events cannot be adequately controlled and measures on system level must be taken in order to prevent the initiating event or diversify the subsystems. The paper specifies an extensive list of common cause initiators from the environment onto software and combines them with fault avoidance and control measures in an event tree method.