Radioactive waste from nuclear or radiological accidents can overwhelm disposal infrastructure, so planners need lessons learned for preparedness. Major accidents at a nuclear power plant or fuel cycle facility are rare but can produce large quantities of radioactive waste with widely varying characteristics that can be difficult to manage. Large volumes of radioactive waste can also be generated by accidents at military installations or by the mishandling high-activity-sealed radiation sources. In the case of a major accident, radioactive waste volumes may quickly overwhelm existing national management and disposal infrastructure. Appropriate disposal facilities might not be available to match the amounts or characteristics of the wastes. This publication is developed to support Member States efforts towards improved preparedness related to the management of radioactive waste in the event of a nuclear or radiological accident. It builds on experiences gained following historic accidents to develop lessons learned, which planners in governmental agencies and nuclear facilities are encouraged to consider in preplanning activities.