Symmetry Breaking in Model Checking of Fault-Tolerant Nuclear Instrumentation and Control Systems

One of the approaches to assure reliability of nuclear instrumentation and control (I&C) systems is model checking, a formal verification technique. Model checking is computationally demanding, but nuclear I&C systems have certain properties that simplify the verification problem. The most notable of these properties are redundancy (duplication of certain system parts in several divisions) and symmetry, which are the means of ensuring failure tolerance. In this work, we extend our previous method of model checking failure tolerance of nuclear I&C systems by proposing an automated symmetry breaking approach that utilizes these properties to simplify the verification problem. As a result, fewer failure combinations need to be checked. We evaluate this approach on a case study that encompasses three safety functions allocated to four I&C systems in the same I&C model.