Assessment of the overall instrumentation and control architecture of the EPR FA3 project

This paper presents the approach used by IRSN to perform the technical assessment of overall instrumentation and control architectures and its application to the EPR Flamanville 3 project. This approach consists in performing a defense in depth and diversity analysis (D3 analysis) with however some specificities to try to overcome the limitations encountered when considering absolute independence between safety classes and lines of defense. Basic assumptions regarding plausible events that may affect I and C devices are set up and are then used as a guideline to systematically screen the robustness of the overall I and C architecture. The application of this approach to EPR is then briefly described. A short description of the architecture and of its underlying concepts is given as well has the main findings. This assessment has allowed identifying a set of specific points requiring additional robustness, with some confidence in being more realistically conservative than with abruptly enforcing high level independence principles. This paper also reminds that in IRSN's approach the assessment of the overall architecture is considered as complementary to the detailed assessment of the I and C systems and equipments, this later being at least as important in terms of both amount of work and confidence brought. (orig.)