Janne Valkonen

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.

Challenges of requirements engineering — A case study in nuclear energy domain

The successful practices of requirements engineering vary between application domains and are characterized by the nature of the application domain. One relatively peculiar application domain is the nuclear energy domain, which is characterized by the long life cycle of power plant operation and construction project, strict control of safety, and collaboration between several stakeholder groups including various branches of technology. We describe the state of the practice of requirements engineering in the nuclear energy domain in Finland on the basis of a descriptive case study focusing on the safety-related automation systems of the nuclear power plants. The results of the study indicate that explicit requirements engineering practices are becoming increasingly important due to the increasing complexity of the technology used, retirement of the older generation of experts, and construction of new power plants along with renewal of the existing nuclear power plants. The challenges of requirements engineering are especially within efficient communication and management of requirements. We highlight challenges that are emphasized by the characteristics of the nuclear energy domain but also discuss the more generic nature of these challenges. The identified challenges are in authority requirements, aging, communication, knowledge transfer, representation of requirements, and tool support.