| The safe recycling of nuclear energy is the focus of the development of nuclear energy at the current stage in China.The application of nuclear energy has made great contributions to the progress and civilization of human society,while it has posed enormous hazards to the natural environment and human health.What's more,the ultimate disposal of nuclear energy is not only related to the safety of the national environment,but has become one of the important factors restricting the cyclical development of the nuclear industry.In recent years,China's nuclear waste treatment technology has been upgraded and disposal facilities are also at a stage of accelerated construction.And the final solidification of nuclear waste has received extensive attention as the core part of the multi-barrier block system.As to the high-level liquid waste with serious harm and the highest treatment difficulty,its treatments are mainly composed of glass solidification and artificial rock solidification.Among them glass solidification is a thermodynamic metastable phase susceptible to water,which contributes the instability of the structure.As a result,the safety of the solidified cement will be affected,if it is stored in a long time.Compared with glass solidification,almost all high-level waste nuclides can be fixed in the artificial rock solidified body with good chemical stability and leaching resistance.At the same time,a large number of medium and low-level radioactive waste is usually treated by cement solidification,which cost less.However,the traditional cement solidification can't reach the anticipated goal due to its poor performance,like limited capacity,high leaking rate and poor radiation resistance.In this paper,common composite Portland cement is prepared as binder,and based on single factor experiments,calcined kaolin and zeolite are selected as additives,and the effects of calcined kaolin,zeolite,waste content and water cement ratio on the properties of solidified body are studied through mixture designs.The optimum solidification formula is composed of waste,composite Portland cement,kaolin and zeolite with a mass ratio of 10:20:3:1.8 and water-cement ratio of 0.5.The optimized formulation is used to simulate the solidified radioactive waste.The retention ability of the solidified body on the radionuclide ion is reduced,but the normalized leaching rate is still 10-7 which meets the requirements of GB 14569.1-2011.At the same time,in order to improve the anti-leaching performance of the solidified body,samples of the surface-coated asphalt solidified body were prepared,and the results showed that the normalized leaching rate of the element was 1 to 2 orders of magnitude lower than that of the original solidified body;Introducing different kinds of fibers into the formulation can improve the crack resistance of the cured body.Among them,when the volume of the polypropylene fiber is 0.3%,the compressive strength is increased by 15.3%to 15 MPa.In the study,as to the difficult disposal of high-level radioactive waste,the effect of sintering temperature and adhesives on the solidification of artificial rocks in syngenetic mineral system was studied,and the leaching rule of solidified elements in immersion solution of pH=2,4,7,11 and 13 was discussed.The results show that the normalized leaching rate of artificial rock solids containing multivalent elements is in the order of 10-510-8,and under the same conditions,the leaching rate of Sr in strong acid environment is higher than that in strong alkaline environment.The artificial rock solidified body has good leaching resistance.Finally,electrochemical impedance spectroscopy?EIS?was used to scan the cement solidified at different ages and the artificial rock.According to Nquist diagram and equivalent circuit diagram,the changing process of the Cured form was explained from the electrochemical signals. |
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