High level waste is waste with levels of activity and radionuclide concentra­tions high enough to generate significant quantities of heat by radioactive decay or waste with large amounts of long-lived radionuclides that need to be considered in the selection of a disposal facility and disposal route for such waste. Handling and storage of HLW requires proper shielding and in some cases also additional cooling. Typical examples of HLW generated at NPPs are highly activated reactor parts. However, the main source of HLW is reprocessing of spent nuclear fuel. Disposal in deep, stable geological formations usually several hundred metres or more below the surface is the generally recognized option for disposal of HLW.