Study On Synthesis Of Silica Based Anion Exchange Resins And Their Application In Thorium Based Spent Fuel Reprocessing

With the expansion of the scale of nuclear power and the growing demand for nuclear fuel,the proven reserves of uranium resources cannot support the development of nuclear power for a long time.Thorium,as a kind of element which can be converted to fissile uranium,is a kind of potential nuclear fuel,which has been widely concerned.In order to realize the efficient utilization of thorium,thorium based fuel reprocessing must be developed.The existing THOREX process is not mature,and there are many problems that can't be solved.Ion chromatography is an efficient method for separation and has a wide range of applications.But the traditional ion exchange resin has poor dynamic performance and poor radiation stability,which is not suitable for the treatment of spent fuel reprocessing process.In order to overcome the defects of traditional ion exchange resin,a noval silica based anion exchange resin was synthesized.In order to achieve the separation and recovery of uranium and thorium,which is the core issue of thorium based fuel reprocessing,adsorption behavior of thorium and uranium in nitric acid solution was investigated,including adsorption mechanism and radiation resistant stability of resin.Finally to achieve efficient separation of thorium and uranium recovery by ion chromatography.The silica based anion exchange resin was successfully synthesized by the method of solution polymerization in the pores of the porous silica support.The silica based anion exchange resin was characterized by SEM,mercury intrusion method,TG-DTA,infrared and other means.The silica based resin has porous structure with the porosity of 37%,and the average pore diameter is 35.3nm.The proportion of organic matter in resin is about 25wt%,and the ion exchange capacity is about 4.2meq/g.In order to realize the adsorption and separation of thorium from nitric acid solution,the adsorption behavior of thorium was studied.With the increase of the concentration of nitric acid,the adsorption ability of the resin to thorium was gradually increased,and reached the best at the concentration of 9M.The adsorption rate of the resin is fast and can reach the adsorption equilibrium in 5min.The adsorption capacity is 28.56mg/g.The adsorption process was in accordance with the quasi two order kinetic equation and Langmuir adsorption isotherm model.The adsorption of thorium by the resin is exothermic reaction.The palladium has strong interference to the thorium adsorption.In the case of no palladium,the resin can selectively adsorb thorium from a variety of fission products.In the nitric acid solution,the adsorption of thorium is much stronger than that of uranium,and the separation coefficient of thorium and uranium in 9M nitric acid is about 10.The 9M nitric acid solution containing thorium and uranium is pumped through a column loaded with silica based anion exchange resin,and thorium and uranium are adsorbed in the column.Uranium is eluted by 9M nitric acid and thorium is eluted by 0.1M nitric acid.Separation and recovery of different concentration ratio of thorium and uranium can be achieved and the recovery rate was more than 99%.The chemical stability and radiation stability of the silica based anion exchange resins were evaluated.After 15 days of immersion in 80 °C nitric acid,the ion exchange capacity of the silica based anion exchange resin remains more than 99%.The radiation stability of the resin was significantly higher than that of the traditional ion exchange resin,and the ion exchange capacity of the resin was still more than 90% when the absorbed dose was 500 kGy in 9M nitric acid.