Study On The Properties Of Phosphate Glass Ceramics Containing Sr(Ⅱ)/Th(Ⅳ) Fluorine Salt Waste

The molten fluorine salt is used as the main coolant in the molten salt reactor,and the fuel of the liquid molten salt reactor itself is dissolved in the high temperature molten salt.In the process of dry reprocessing of spent fuel in molten salt reactor,analysis of fuel salt,separation and recovery of fuel carrier salt,molten salt waste with fluorine salt as the main component will be produced.The characteristics of molten salt waste include strong radioactivity,corrosiveness,poor chemical stability,easy deliquescence,low melting point,and high radioactivity may also cause the radioactive decomposition of waste salt to form halogen-containing gas.Some wastes may contain toxic components such as beryllium fluoride.Many of these molten salt wastes exist in dispersed or mobile forms,such as particles or powders such as sodium fluoride,magnesium fluoride and barium fluoride produced by high temperature fluorination volatilization treatment of fuel.How to deal with this kind of molten salt waste with strong radioactivity,chemical corrosion and chemical toxicity is a difficult problem to be solved in the development of molten salt reactor and dry process reprocessing.Because the encapsulation rate of borate glass to chloride and fluoride is very low,the traditional curing technology based on borosilicate glass is not suitable for the treatment of molten salt waste produced by dry treatment,so it is necessary to develop suitable curing technology for molten salt waste.On the basis of the characteristics of waste produced by dry treatment,this paper puts forward the curing scheme of many kinds of glass ceramic solidifying bodies by using SrF₂and ThF₄as simulated waste after component design.The structure and chemical stability were analyzed and compared in detail,the composition and preparation process of vitreous ceramic solidified body were optimized,the relationship between waste inclusion and the leaching resistance of solidified body was studied.This paper consists of six chapters:The first chapter is the introduction.This paper briefly introduces the development background of molten salt reactor,expounds in detail the source,composition and characteristics of molten salt reactor waste,and focuses on the research status of waste solidification from dry process reprocessing at home and abroad.Based on the analysis of the investigation results,the iron phosphate glass powder and the precursor of strontium fluoride and thorium fluoride ceramic powder were uniformly mixed and sintered by solid phase sintering technology to obtain the molten salt waste glass ceramic solid.By analyzing the composition of fluoride salt waste,a reasonable substitute and target crystal were selected,and the curing formula was designed according to the composition of the target crystal and verified by experiments.The second chapter is the introduction of experimental research methods.The raw materials,the source of reagents and the equipment of the experiment solidified substrate are briefly introduced,the experimental scheme adopted in this study is described in detail,and the method of analyzing and characterizing the solidified body in the experiment is described in detail.Chapter 3 is about the structure and chemical stability of Th（Ⅳ）fluoride waste glass solidified body.A portion of radioactive waste generated in thorium-based molten salt reactors（TMSR）will exist as fluoride.Due to the low solubility of fluoride in borosilicate glass,this glass curing system is no longer applicable.Previous studies have shown that iron phosphate glass is more inclusive of fluoride.In this chapter,thorium fluoride is used as a typical 4-valent analog nuclide to prepare iron phosphate glass solid with different mass fraction,and XRD,SEM,PCT experimental methods are used to analyze the structure and chemical stability of the solid.Chapter 4 is about the structure and chemical stability of Sr（Ⅱ）fluorine salt waste glass ceramic solidified body.Salt wastes containing halides in molten salt reactor systems are unstable during storage in containers.These wastes can be fixed by glass ceramics.SrF₂fluoroapatite ceramics were prepared in this chapter,and then encapsulated with iron phosphate glass.The glass ceramic solid was prepared by solid phase sintering.The structure and properties of fluoroapatite ceramics and glass ceramics solidified body were analyzed.Chapter 5 is about the structure and chemical stability of Th（Ⅳ）fluorine salt waste glass ceramic solidified body.As the main content of this chapter,two kinds of ceramics containing ThF₄ammonite and thorium stone are prepared,then encapsulated with iron phosphate glass,and two kinds of glass ceramic solidified bodies are prepared by solid phase cantering.The structure and properties of two kinds of ceramic and glass ceramic solidified bodies were analyzed.Chapter 6 is the summary and outlook.This paper summarizes the research contents and results,summarizes the problems found in the research process,analyzes some ideas to solve these problems,and prospects the future research.