The Nuclear Energy Agency (NEA) and the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) are organising an international workshop on the characterisation of large quantities of unconventional and legacy waste. The event will take place in Iwaki, Japan on 31 August - 1 September 2022. This workshop builds on the work of the NEA Expert Group on Characterisation Methodology of Unconventional and Legacy Waste (EGCUL) and its report Management of Radioactive Waste after a Nuclear Power Plant Accident published in 2020. The workshop aims at supporting the progress of the clean-up of Fukushima Daiichi nuclear power plant. The workshop will convene participants from various fields of expertise in the areas of radioactive waste management, decommissioning, nuclear science and development, as well as young professionals, communication experts and researchers.