[en] The objective of this project was to make a contribution toward the goal of improving nuclear plant performance by identifying conservatisms and uncertainties in the determination of core power distributions. This objective was achieved by investigating incore instrumentation measurements and the interpretation and conversion of these measurements to power distributions. The data base for this analysis consisted of incore detector measurements for two PWRs (Westinghouse) and two BWRs and gamma scan measurements for two BRWs and one PWR. The conclusions and results presented for the analysis of incore detector measurements were based on evaluations of measurement asymmetries and trends throughout one cycle of data for each plant investigated