Model checking of safety-critical software in the nuclear engineering domain

Instrumentation and control (I&C) systems play a vital role in the operation of safety-critical processes. Digital programmable logic controllers (PLC) enable sophisticated control tasks which sets high requirements for system validation and verification methods. Testing and simulation have an important role in the overall verification of a system but are not suitable for comprehensive evaluation because only a limited number of system behaviors can be analyzed due to time limitations. Testing is also performed too late in the development lifecycle and thus the correction of design errors is expensive. This paper discusses the role of formal methods in software development in the area of nuclear engineering. It puts forward model checking, a computer-aided formal method for verifying the correctness of a system design model, as a promising approach to system verification. The main contribution of the paper is the development of systematic methodology for modeling safety critical systems in the nuclear domain. Two case studies are reviewed, in which we have found errors that were previously not detected. We also discuss the actions that should be taken in order to increase confidence in the model checking process.

► We introduce methodology for model checking safety critical systems.
► We show two case studies in which an error was found through model checking.
► Typical errors are infrequent scenarios where events occur during a short time frame.
► Confidence can be gained by a well-defined and documented process.
► Formal methods in system verification should be rigorously demanded in standards.