Power Reconstruction Uncertainties in European Pressurized Reactor Impact of Partial. Unavailability of Sensors

Abstract: This study is part of a theme related to the physical tests performed on the core of nuclear reactors and particularly the EPR, a new French reactor under construction on the Flamanville site. The peaking factors of this reactor are continuously monitored by an instrumentation located both inside (collectrons) and outside (external fission chambers) the core. To ensure maximum accuracy, these instruments are periodically calibrated by a more precise measurement of the distribution of neutron activity in three dimensions carried out by the AMS (Aeroball Measurement System). Flux maps, providing this data, are collected during operation. Once the data have been recorded on certain assemblies, they are extended to all the assemblies and rods in the core in a mathematical process called $reconstruction$. The objective of this project is therefore to study the impact of partial unavailability of the AMS device, which can occur in the event of breakdowns, on the uncertainty linked to the reconstruction of the neutron power in the core. However, in the absence of measurements for the EPR reactor, pseudo-measurements will be generated. These correspond to core perturbations such as azimuthal power imbalance, radial power imbalance or more unpredictable perturbations.The results for these different disturbances are analyzed and compared to design criteria by selecting the most penalizing situations. In conclusion, these results bring answers to the question of maximum permissible unavailability of AMS in the context of the startup of the EPR reactor in Flamanville.