How much uncertainty surrounds radioactive waste predictions? This paper clarifies the uncertainty in predictions of the quantity, radionuclide inventory, and activity of waste from the Krsko nuclear power plant. The study uses scenario analysis to assess how waste characteristics vary based on factors such as plant operating lifespan and fuel enrichment levels. This study focuses on waste generated by U-235. Calculations connected to spent fuel were performed using ORIGEN2 computer code. A separate code was developed for calculating low- and intermediate-level waste. This dual approach allows for a comprehensive assessment of waste characteristics across different categories. Ultimately, the research presents and interprets the results in a manner accessible to decision-makers and the general public. By clarifying these issues, the study aims to contribute to more informed decision-making and build confidence in waste management options, concerning health and environmental management as well as nuclear technology.