Reliability Improvement and Assessment of Safety

In order to allow the introduction of safety-related Digital Instrumentation and Control (DI&C) systems in nuclear power plants, the software used by the systems must be demonstrated to be highly reliable. The most widely used and most powerful method for ensuring high software quality and reliability is testing. An integrated methodology is developed in this thesis for reliability assessment and improvement of safety critical software through testing. The methodology is based upon input domain-based reliability modeling and structural testing method. The purpose of the methodology is twofold: Firstly it can be used to control the testing process. The methodology provides path selection criteria and stopping criteria for the testing process with the aim to achieve maximum reliability improvement using available testing resources. Secondly, it can be used to assess and quantify the reliability of the software after the testing process. The methodology provides a systematic mechanism to quantify the reliability and estimate uncertainty of the software after testing. Acknowledgments The author would like to acknowledge ABB-Combustion Engineering for their generous permission for us to use their proprietary software and supporting documents in our case study. Special thanks go to Michael Novak, the primary contact-person at ABB-CE, for his comments, clear focus of requirements upon our research. Thanks also go to Hamilton Technology Inc. for supplying the 001 system for use in the project. Special thanks go to Ronald Hackler for his technical guidance in using the wonderful features of the 001 system.