Experimental Study On The Treatment Of Emergency Drinking Water Under Severe Nuclear Accident By Membrane Technology

After the Fukushima accident, the problem of water resource security under nuclear accident has gradually become a hot research topic. This thesis reviews the three nuclear accident during the history of nuclear power development and the pollution caused by those nuclear accident. The 131 I released from the reactors, having a short life, had decayed away quickly. The presence of long-lived nuclides, which may be the major source of radioactivity above background levels in the area for many decades to come, can be removed by conventional water treatment technology, but the removal efficiency of this technology is not satisfactory.In this thesis, we studied two types of pressure driving membrane, namely nanofiltration membrane and reverse osmosis membrane, to remove the target nuclide. In consideration of the characteristics, types and harm about the nuclides in the polluted surface water, we choose Co2+, Cs+ and Sr2+ as research object. When considering about the influence factor of the membrane treatment, separation model and rules are also introduced in this thesis. At last, we discussed the feasibility of the combined process, which consist of coagulation sedimentation, sand filtration, activated carbon adsorption and reverse osmosis, to treat simulated polluted surface water. The following experimental conclusions can be obtained:(1)To investigate the elimination effect of flat nanofiltration membrane device to remove radionuclides from emergency drinking water when severe nuclear power plant accident happened, the effects such as pressure, p H and operation time on the retention efficiency of non-active nuclides cobalt, cesium, strontium and effluent conductivity were explored. With the increase of operation pressure, the removal rate of nuclide by the nanofiltration membrane increased and the conductivity of the effluent decreased. But instead, when the pressure increases to 1.2MPa, the removal rate of nuclide by the nanofiltration membrane decreased and the conductivity of the effluent increased. In alkaline condition, the performance of nanofiltration membrane to removed Co2+, Cs+ and Sr2+ got better.(2) The effects such as nuclides concentration, pressure, p H, competing ions on the retention efficiency of non-active nuclides cobalt, cesium, strontium and effluent conductivity were explored by using TW30-1812 low pressure reverse osmosis membrane. The experimental results showed that inflow nuclides concentration had no significant effect on nuclides retention rate. With increasing inflow p H, the rejection of nuclides increased; when the p H was higher than 9, the retention efficiency increased very slowly. The inflow calcium ion concentration had the greatest impact on the rejection of cesium ions; when the calcium ion concentration increased to 250 mg/L, the rejection coefficient of cesium decreased to 77.4%.(3) The combined process, including coagulation, sand filtration and activated carbon, can reduce TOC, nuclides concentration and conductivity efficiently. The optimum coagulant dosing quantity is 50 mg/L. Alkaline solution contribution to the coagulate effect. Reverse osmosis membrane made the largest contribution to the reduction of TOC, nuclide concentration and conductivity. After the treatment of combined technology, TOC value of water samples reduced form 7.19 mg/L to 0.148 mg/L.