基于水化硅酸镁胶凝体系的核废料固化材料分子结构及吸附性能研究

Cement solidification technology has been used for immobilization of low-level radioactive waste and intermediate level radioactive waste widely. However, the traditional Portland cement / Alkali Activated Slag Cement system has high water-cement ratio, high radionuclide leaching rate and low compressive strength. Compared with ordinary Portland cement, magnesium silicate hydrate cement system has lower pH and porosity, lower baking temperature, higher compressive strength and lower heat of reaction, which helps to slow the migration rate of activated ion in nuclear waste, and also helps to improve the ability of immobilization. It is used in this project to immobilize the low / intermediate level nuclear waste. XRD( Software TOPAS), NMR will be used to learn the change of hydration product and the molecular structure of magnesium silicate hydrate (M-S-H) gel, to provide the mechanism of setting and hardening; the pore structure of magnesium silicate hydrate and the molecular structure of magnesium silicate hydrate gel will be explored, and the effect of different environment for stability and adsorption properties of magnesium silicate hydrate system will be proven. The adsorption and immobilization properties of Cs and Sr in magnesium silicate hydrate system will be analyzed to provide a theoretical basis and scientific foundation for the cement to be used in low/ intermediate level nuclear waste immobilization.

水泥固化技术运用在低中放射性核废料的处理上有着明显的优势，然而传统的硅酸盐水泥/碱矿渣水泥处理技术存在水灰比高、核素浸出率高和固化体强度低等不足。相比之下，水化硅酸镁胶凝体系具有低碱度、免烧成、孔隙率低、强度高和反应热低且平稳等特点，有利于降低核废料中活化离子的迁移能力，也有助于固化能力的提高。本课题将选用该体系作为低中放核废料的固化材料，利用XRD（TOPAS软件）和NMR对其物相变化和水化硅酸镁(M-S-H)凝胶的分子结构进行定性定量分析，提出凝结硬化机理；利用氮吸附和脱附测试技术进行比表面积和孔隙结构分析，探索不同环境对于该体系体积稳定性及吸附性的影响；将常见低中放核素铯和锶固化于该体系中，深入研究其吸附性能及固化作用机理，为水化硅酸镁胶凝体系水泥应用于低中放核废料的固化提供理论依据和科学基础。

基于传统水泥固化核废料技术存在不足的问题，提出将低碱度水化硅酸镁胶凝体系应用于核废料固化，并对体系水化产物的分子结构及其对核废料的吸附性能、固化机理进行深入研究。通过定量分析各龄期时体系的水化反应产物，总结出MgO-SiO2-H2O胶凝体系四个阶段的反应进程，并根据SiO2的溶解程度建立了反应动力学模型，探明pH值和Na-HMP对MgO-SiO2-H2O胶凝体系的影响，确定了Na-HMP含量和初始pH值的最佳值。含Cs+、Sr2+、废树脂的固化体力学性能、耐久性能及浸出性能均满足标准GB14569.1-2011中的要求，通过物相组成和微观结构分析，探明MgO-SiO2-H2O胶凝体系对核素Cs+和废树脂固化主要通过水化产物的物理包覆和吸附作用，而对Sr2+的固化主要通过化学结合和水化产物的物理包覆。