Biotransformation of Neptunium in Model Groundwaters

—The kinetics of Np(VI and V) reduction was studied in model underground water in the presence of bacteria, isolated from from deep-injection disposal of liquid radioactive wastes of Siberian Chemical Plant. Obtained data indicate a chemical instability of Np(VI) in the studied system. The reduction of neptunium (V) depended on its initial concentration and the presence of microorganisms. In microbiome samples, the reduction rate has significantly increased and neptunium-bearing particles more than 200 nm in size were formed. At neptunium concentrations less than 10 –7 М, the reduction rate constant did not depend on the radionuclide content (half-reaction period of 36–40 days). An increase of Np concentration to 10 –6 М led to a two-fold decrease of the reduction rate constant.