Apparatus and methods for treating radioactive material, in particular for cleaning radioactive contaminated water, are described. One apparatus comprises a process chamber with a combustion zone for generating an oxygen rich gas and an oxidation zone, which is arranged to receive the oxygen rich gas from the combustion zone. The process chamber further comprises a feed opening for feeding the radioactive material into the oxidation zone and is configured to use the oxygen rich gas for oxidizing the radioactive material to obtain oxidized material. The apparatus further comprises a separation device operationally connected to an outlet of the process chamber and configured to at least partly separate the oxidized material into a gaseous fluid and a non-gaseous residue. This way a greatly reduced volume of the radioactive material is achieved, enabling safe and efficient handling and/or compact and space-saving disposal of the radioactive material.