Development of Software Test-based Reliability Assessment Method for Nuclear Power Plant Safety-critical Software

Abstract

Software has been used to digitalize many instrumentation and control (I&C) systems in nuclear power plants (NPPs). Since software failure induces the common cause failure of the processor modules, the reliability of the software used in NPP safety-critical I&C systems must be quantified and verified with proper test cases and environment. In this study, a software testing method using the simulation-based software test-bed is proposed. In the test-bed, the microprocessor architecture of the programmable logic controller (PLC) used in NPP safety-critical applications is emulated and the execution behavior of the microprocessor at each machine instruction line is captured. The effectiveness of the proposed method is demonstrated with the safety-critical trip logic software of a fully digitalized reactor protection system (IDiPS-RPS). The software test cases are developed in consideration of the digital characteristics of the target system as well as the plant dynamics to represent the possible states of software input and internal variables that contributes to generating its dedicated safety signal. The method provides a practical way to conduct software testing in order to prove the software to be error-free while effectively reducing the software testing effort by emulating the PLC behavior in machine-level compared to existing software testing methods.