Multi-fragmental Markov’s Models for Safety Assessment of NPP I&C System Considering Migration of Hidden Failures

Abstract

The information and control systems of Nuclear Power Plant and other safety critical systems are considered as a set of three independent hardware channels including online testing system. Nuclear Power Plant information and control systems design on programmable platforms is rigidly tied to the V-model of the life cycle. Safety and availability during its life cycle are assessed using Markov and multi-fragmental models. The multi-fragmental model MICS32 contains an absorbing state in case of hidden faults and allows evaluating risks of “hidden” unavailability. The MICS42 model simulates the “migration” of states with undetected failures into states with detected faults. These models describe the functioning of the system and the complete elimination of software faults. Results of multi-fragmental modeling are compared to evaluate proof test period taking into account requirements for SIL3 level and limiting values of hidden fault probabilities. Multi-fragment models are included in the assessing method of implementation safety requirements of ICS on programmable platforms. The information technology of decision support in assessing and managing the implementation of the requirements for ICS safety is also considered.