Study On The Treatment Of Liquid Radioactive Waste In Nuclear Power Plant By Ferrite Co-Precipitation Process

With the continuous development of nuclear power utilization, the treatment of liquid radioactive waste in nuclear power plant has been a hot and thorny topic, and it is particularly important to treat activated corrosion products with the higher level radioactivity.60Co is the typical activated corrosion product in liquid radioactive waste from nuclear power plant, the proportion is more than40%, it has high toxicity, long half-life, high energy γ-photons, and will lead to serious harm to the environment and human health if it is not properly treated. Therefore, it is vital significant to remove60Co in liquid radioactive waste.In this study59Co has been used as the simulation of non-radioactive isotope, and the process parameters, sediment characteristics and mechanism of ferrite process have been investigated, which is applied to remove Co2+in the simulated liquid radioactive waste. It will provide reference to use ferrite process for the treatment of the actual liquid radioactive waste. Experimental results are as follows:(1) Ferrite process can efficiently remove Co2+in the simulated liquid radioactive waste. Under the optimal process parameters, residual Co2+≈0.50μg/L in effluent, and DF≈10000. To treat100mL liquid waste, the average weight of wet sediment produced is0.6155g, the average weight of dry sediment is0.0673g, and water content is89.06%. The magnetism of wet sediment is week, and it is not good for magnetic separation. Decreasing the concentration of boric acid, increasing pH or rising temperature are all able to improve magnetism of wet sediment slightly. The use of Fe3O4as seed crystal can improve magnetism of wet sediment significantly, which is beneficial to magnetic separating. Ferrite process with seed crystal (FPSC) has good performance on treatment efficiency and magnetic separating. Under the optimal process parameters, residual Co2+≈0.36μg/L in effluent, and DF>10000.(2) FPSC has good removal efficiency on Co2+, Cu2+, Zn2+and Mn2+. Cu2+, Zn2+and Mn2+decrease the removal efficiency of Co2+to various degrees. Under the optimal process parameters, residual Co2+≈0.40-0.50μg/L in effluent, and DF>1.0×104. Moreover, residual Cu2+, Zn2+and Mn2+are all less than5.00μg/L. When single ion exists, the DF sequence is Co2+> Mn2+> Cu2+> Zn2+; when three ions coexist, the sequence is Co2+> Cu2+> Mn2+> Zn2+(3) The water quality parameters, including pH, DO, ORP and conductivity change obviously during the NaOH titrating process in FPSC, and removal efficiency of Co2+is 99.98%when the titration process ends. The stage of ferrite crystal formation starts mainly after the titration process, the magnetism of sediment improves and the magnetic separating becomes possible. XRD, VSM and XPS analysis show that ferrite sediment is crystalline in nature with cubic structure, and contains ferrite crystal CoFe2O4and Fe3O4. It has ferromagnetism at ambient temperature, Hc=137.902Oe, Mr=5.852emu/g, and Ms=47.72emu/g. The iron-containing compounds include Fe3O4, CoFe2O4and Fe2O3on the surface of sediment.(4) It is successful to treat the actual liquid radioactive waste from Third Qinshan Nuclear Power Plant by the FPSC, the removal efficiency of total radionuclide is96.95%, and60Co is99.72%. Moreover, the supernatant is very clear, the magnetism of wet sediment is strong, magnetic separation is good, and the weight of dried sediment is0.6185g to treat500mL liquid radioactive waste.