Abstract: The invention relates to a method and apparatus for the reduction in the quantity of low activity organic wastes from nuclear power plants. This is accomplished using anaerobic fermentation in a bioreactor. The waste from the nuclear power plant is subjected to a pretreatment such as comminution and suspension, hydrolysis and/or physical dispersion, such as by a irradiation, heat treatment or the equivalent. The pretreated waste is subjected to anaerobic decomposition in a bioreactor, the anaerobic decomposition taking place in two stages, namely an acid stage and a methane stage. The gases produced in the decomposition process are conducted from the methane stage to a gas burning stage and the undecomposed waste is removed, concentrated and packed in barrels or the like for storage.