Exhaustive testing of safety-critical software for reactor protection system

Abstract As software is used to implement safety-critical functions in nuclear power plants (NPPs), the software developers must demonstrate that the software will generate its dedicated safety signal in on-demand situations based on proper test results to ensure the safety of digitalized NPP. This paper describes an automated exhaustive test case generation framework for the function block diagram (FBD) programs used in NPP safety systems. The proposed method translates an FBD program to a semantically equivalent satisfiability modulo theories (SMT) formula based on the formal definition of FBD and generates the exhaustive test cases given desired software output by iteratively solving the SMT formula. The effectiveness of the proposed framework is demonstrated with a case study of a trip logic software of a typical NPP reactor protection system. The case study results showed that the proposed approach could effectively generate exhaustive test cases and further prove that the NPP safety software is error-free in terms of its safety function.