Model-Based Analysis of an Arc Protection and an Emergency Cooling System:MODSAFE 2007 Work Report

Instrumentation and control (I&C) systems play a crucial role in the operation of nuclear power plants and other safety critical processes. An important change that will be going on in the near future is the replacement of the old analogue I&C systems by new digitalised ones. The programmable digital logic controllers enable more complicated control tasks than the old analogue systems and thus the verification of the control logic designs against safety requirements has become more important. In order to diminish the subjective component of the evaluation, there is a need to develop new formal verification methods. This report summarizes the work done in the MODSAFE 2007 project on two case studies where model checking techniques have been used to study an arc protection system and an emergency cooling system. Model checking tools offer typically a finite state machine based modelling language for modelling the system to be verified, a specification language (temporal logic) for expressing the properties to be verified and a set of analysis tools to check that the system satisfies the given properties. A state of the art open source model checking system NuSMV was employed and using a reasonable effort it was possible to (i) model both systems on an adequate level, (ii) to formulate required safety properties in the specification language, and (iii) to perform a full verification of the properties using the NuSMV system. This indicates that current model checking techniques are applicable in the analysis of safety I&C systems in NPPs