Radioactive waste represents only a small portion of the waste produced by human activity. However, it is dangerous due to its potential long-term negative effects on the biosphere. Close attention is therefore paid to the handling and storage of radioactive waste. Radioactive waste may be classified according to its radioactivity level as low-level, intermediate-level, or high-level radioactive waste and according to its state as solid, gaseous or liquid waste. Each type of radioactive waste requires different handling, a different system of storage and processing, and also a different final storage in repositories where this waste will be safely isolated for a sufficiently long period of time from the environment. A deep repository is a locality where long-term radioactive waste will be isolated from the biosphere for up to one million years.