| A certain volume of radioactive organic waste liquid and radioactive waste water containing organic matter will be generated during nuclear material production,nuclear facility operation,maintenance and decommissioning.Due to the existence of organic matter,conventional inorganic radioactive waste liquid treatment methods or solidification methods cannot be used for treatment.For this part of the waste liquid,this paper adopts the combined treatment method of supercritical water oxidation+ultrafiltration+reverse osmosis+membrane distillation.Supercritical water oxidation is used to destroy and decompose organic matter,ultrafiltration+reverse osmosis is used to purify and decontaminate the radioactive waste liquid which was treated by supercritical water oxidation,and membrane distillation is used to purify and reduce the volume of the reverse osmosis concentrate.For the supercritical water oxidation unit with a processing capacity of 8 L/h.A typical simulation environment processing experiment was carried out.The oxidative decomposition of the supercritical water oxidation unit on the radioactive organic waste liquid containing 30%TBP/kerosene,Mobil light oil,and Mobil intermediate oil was investigated.The research results show that this supercritical water oxidation unit can oxidize and decompose almost all organic matter,and the chemical oxygen demand(COD)removal rate is above 99.93%.In the ultrafiltration+secondary reverse osmosis treatment unit,the ultrafiltration membrane module is a rolled polyethersulfone composite membrane with a molecular weight cut-off of 1000 Daltons,and the reverse osmosis membrane module is a rolled aromatic polyamide composite membrane with a molecular weight cut-off of 100 Daltons.Apply this set of ultrafiltration+secondary reverse osmosis treatment unit to purify and decontaminate the radioactive waste liquid which was treated by supercritical water oxidation,the research results show that the decontamination factor for radioactive waste liquid is above 7.1×10~3,and the rejection rate of radioactive metal ions is above 99.97%.The effects of operating pressure,feed pH and ion concentration on membrane flux and rejection rate were investigated.The results show that operating pressure has the most significant effect on membrane flux of ultrafiltration and reverse osmosis.When the operating pressure increased from 0.6 MPa to 1.4 MPa,the membrane flux of reverse osmosis increased from 9.84 L/m~2·h to 23.03 L/m~2·h,the membrane flux increased by 134.04%.The feed pH is the most significant factor affecting the rejection rate of ultrafiltration and reverse osmosis,when the feed pH increased from 7 to 9,the Co(II)rejection rate of ultrafiltration increased from 27.07%to 63.38%.For the air-gap membrane distillation unit with PTFE membrane with a pore size of0.22μm.The influence of the feed temperature and the feed flow rate on the membrane flux and rejection rate was investigated.The results show that the feed temperature is the most significant factor affecting the membrane flux.When the feed temperature increased from 50℃to 90℃,the membrane flux increased from 3.51 kg/m~2·h to 15.48 kg/m~2·h,and the membrane flux increased by 341.03%.Feed temperature and feed flow rate have almost no effect on the rejection rate.Finally,a long-term continuous membrane distillation experiment was conducted on the PTFE membrane with a pore size of 0.22μm to investigate its performance under long-term continuous operation conditions.The results of the study show that the PTFE membrane with a pore size of 0.22μm always maintains perfect performance throughout the operating time,the rejection rate of each radioactive metal ion remained above 99.97%,and the decreasing trend of membrane flux was not obvious. |
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