OECD/NEA WGRISK task on failure modes taxonomy for digital I&C - DIGREL

초록

The OECD/NEA CSNI Working Group on Risk Assessment (WGRisk) has set up a task group called DIGREL to develop a taxonomy of failure modes of digital components for the purposes of probabilistic risk analysis (PRA). The failure modes taxonomy is based on a failure propagation model and a definition of five levels of abstraction: 1) system level, 2) division level, 3) I&C unit level, 4) I&C unit modules level, 5) basic components level. This structure corresponds to a typical reactor protection system architecture. The failure propagation model consists of the following elements: fault location, failure mode, uncovering situation, failure effect and the end effect. These concepts are applied to define the relationship between a fault in hardware or software modules (module level failure modes) and the effect on I&C units (I&C unit level failure modes). The purpose of the taxonomy is to support PRA, and therefore focuses on high level functional aspects rather than low level structural aspects. This focus allows handling of the variability of failure modes and mechanisms of I&C components. It reduces the difficulties associated with the complex structural aspects of software in redundant distributed systems.

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