peer reviewed ; How does naming an object affect the way it is or could be managed? This paper examines and compares classification systems for radioactive waste applied by the IAEA and in France, Canada and Belgium. I analyze how the relevant actors classify radioactive objects and, in so doing, prescribe their management. By comparing and describing four established classification systems, I highlight how the IAEA and national classification systems for radioactive waste systematically associate the “high-level radioactive waste” category with the “deep geological disposal” option. Building on Science and Technology Studies, I argue that creating categories of high-level radioactive waste does more than just describe different types of wastes: it also prescribes certain management options (e.g. deep geological disposal), thereby opening up certain options for action and closing down others. I underline how uncertainties remain about what to do with radioactive wastes in blurred, un-stabilized categories that are classified and named differently by different actors. Examples of “blurred” categories include spent nuclear fuel from uranium oxide, and spent nuclear fuel from mixed oxide fuel (MOX). Should these categories be managed as a waste, or as a resource? Should their common fate be the deep geological disposal? Revealing the power and limits of a top-down classification system to manage radioactive waste, I maintain that remaining uncertainties could reverse the dynamics of imagining a final long-term repository option for a given category. In the absence of stabilized categories, the deep geological disposal option becomes the primary mode of classifying objects as either waste or a resource. This analysis flips the conventional notion of high-level radioactive waste on its head: instead of asking what management option should be preferred to deal with nuclear waste, the chosen disposal option has a decisive influence on what counts a radioactive waste in the first place. Nuclear engineers and top nuclear ...