A Software Fault Tree Analysis Technique for Formal Requirement Specifications of Nuclear Reactor Protection Systems

Rigorous safety demonstration of software, as well as systems, is required when developing digital reactor protection systems in nuclear power plants. Various safety analysis techniques try to identify, analyze, and find remedies for potential hazards at each stage of software development life-cycle. This paper proposes a software fault tree analysis technique for software requirements written in the NuSCR formal specification language. The proposed method can mechanically construct software fault trees and calculate minimal cut-sets, encompassing timing constraints of multi-cycles, from NuSCR formal specifications. We also improved the fault tree construction and analysis tool into "NuFTA 2.0" to cope with multi-cycled executions. The case study with a preliminary version of requirements specification for a Korean nuclear power plant in operation shows the proposed technique's effectiveness and applicability to other V&Vs such as simulation.