Radioactive waste drums containing nuclear material pose a significant challenge in the context of JRC-Ispra decommissioning and waste management, both for the alpha emitting radionuclide content and for the safeguards implications. Accurate characterization of these drums is therefore essential for the safe management of nuclear waste. In this paper, we describe the use of differential die-away technique neutron measurements (DDT) and gamma spectrometry for the characterization of radioactive waste drums containing Uranium Hexafluoride (UF6). Our results show that the combination of these techniques provides a highly accurate and sensitive means of characterizing these drums, including the mass and the FRAM-evaluated enrichment of Uranium, as well as the consequent alpha activity. We also discuss the general benefits of using DDT in waste characterization, specifically the ability to non-invasively detect and quantify the fissile content of the drums. Our findings highlight the importance of nuclear material characterization in the management of nuclear waste.