NPP Krško is a 650 MW nuclear power plant, located in the Republic of Slovenia. When Krško was built it was planned to construct the low/intermediate radioactive waste repository in the following 10–15 years. There has been considerable delay in the repository project implementation and Krško on site temporary radioactive waste storage was almost full. As the part of NPP efforts to solve the problem, a supercompaction campaign has been carried out, during which almost 90% of the existing drums were supercompacted and put into the new overpacks. The overpack is a steel tube type container (TTC), licensed as an IP 2 IAEA package type. The final volume reduction achieved was 30% of the original volume, which ensures additional storage space for at least five years of normal plant operation. At the same time, a detailed characterisaiion of each drum before compaction, including radionuclide inventory, has been done.