Input-Domain Software Testing for Failure Probability Estimation of Safety-Critical Applications in Consideration of Past Input Sequence

Software failure probability quantification is an important aspect of digital system reliability assessment. Several quantification methods currently available in the software reliability field have characteristics unsuitable for application to safety-critical software. In this paper, a software test framework in consideration of input trajectory is developed, and a software failure probability quantification method is also suggested. The test input cases consist of the states and present inputs, where input trajectory is represented by the state. To obtain the input domain, which represents realistic plant behavior, digital system characteristics and plant dynamics are considered. This allows software failure probability to be estimated by using the result of each representative test case, thus reducing testing efforts. The proposed framework was applied to a nuclear power plant reactor protection system as an example to show its effectiveness. The method provides a practical and relatively simple way to test software and estimate software failure probability.