An experience of a critical software development

Some data about the design and validation of a safety critical software, the ESIN application software, are presented. The ESIN application software is integrated within an instrumentation system designed for experimental nuclear reactors. Its main function is to generate the emergency shutdown of the reactor. The development of this software has been based on a fault-avoidance approach: use of a strict life cycle, existence of an independent verification and validation team, and application of rules of design and programming. The data presented here concern the location of faults in the life cycle and in subsystems; a classification of faults in each step is provided. These data are also correlated with the effort spent on verification/qualification.<>