次锕系核素在钙钛锆石基玻璃陶瓷中的固化机制

The disposal of high level radioactive waste (HLW) is one of the critical factors to promote the sustainable development of exploring and utilizing nuclear energy. As the first barrier of multi-barrier system in the deep geological disposal method, the choice of HLW waste form is significantly important. Glass-ceramic matrix, which offers the best flexibility to combine the advantages of glasses and ceramics and avoid their respective disadvantages, is one of the most promising matrices to immobilize HLW. In this proposal, the zirconolite-based glass-ceramic matrix will be chosen to immobilize the simulated minor actinides. Concerning the co-existence of lanthanides and actinides in the domestic minor actinides waste, representative lanthanides (La, Ce, Nd and Gd) will be used as the surrogates of minor actinides. This study will focus on the immobilization mechanism of different simulated minor actinides with using zirconolite-based glass-ceramic matrix. With techniques such as Rietveld structural refinement, Rietveld quantitative XRD, TEM-EDX, SAED and Mössbauer spectroscopy, the existing forms and immobilization and occupation mechanisms of the simulated minor actinides in the zirconolite-based glass-ceramic matrix will be revealed. The leaching behavior of the simulated minor actinides from the zirconolite-based glass-ceramic matrix will also be studied to reveal the chemically-resistant mechanism. In addition, the effects of Fe and Mo contents on the immobilization mechanism, charge compensation mechanism and leaching mechanism of the simulated minor actinides in the zirconolite-based glass-ceramic matrix will be further studied. With the information integrated in this project, an innovative and reliable technology for safely disposing China’s minor actinides waste will be developed.

高放核废的安全处理与处置是核能可持续开发利用的一个关键因素。作为多屏障深地质处置的第一道屏障，高放废物固化体的选择极其重要。玻璃陶瓷固化体可以融合玻璃和陶瓷的优点和消除两者的缺点，是最有应用前景的高放废物固化基材之一。本项目拟以最具挑战性的次锕系核素固化为研究对象，利用钙钛锆石基玻璃陶瓷固化次锕系模拟核素,并研究其中的固化机制和稳定性。选择La、Ce、Nd和Gd为代表性次锕系模拟核素，借助Rietveld XRD、透射电镜和穆斯堡尔谱等分析方法揭示各个次锕系模拟核素在钙钛锆石基玻璃陶瓷中的赋存形态、固化机制和电荷补偿机制。研究钙钛锆石基玻璃陶瓷固化体中次锕系模拟核素的浸出行为和浸出规律，阐明固化体对核素的抗浸出机制。同时，研究Fe和Mo的掺杂对钙钛锆石基玻璃陶瓷固化次锕系模拟核素的赋存形态、固化机制、电荷补偿机制和抗浸出机制的影响。本研究为安全处置我国富锕系高放废物提供可靠的科学依据。

玻璃陶瓷基材作为一种最具有前景的高放核废固化体，可以很好的融合玻璃和陶瓷的优点和消除两者的缺点。本项目以钙钛锆石作为玻璃陶瓷基材的结晶相进行研究，同时考虑Fe2O3和MoO3对玻璃陶瓷体系的影响。本项目系统研究了CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O 体系在成核晶化过程中，基材的短程序、中程序和长程序的结构演变，揭示了中程序结构在成核晶化中的重要作用。研究了Fe2O3对CaO-Al2O3-SiO2-TiO2-ZrO2-CeO2-Na2O玻璃形成钙钛锆石玻璃陶瓷基材的影响。探讨了两步结晶法中Fe2O3对表面结晶的影响，研究了热处理过程中玻璃陶瓷基材的局域结构的演变，并发展了一步结晶法以获得低表面结晶的钙钛锆石玻璃陶瓷基材。研究了MoO3对玻璃体系形成钙钛锆石玻璃陶瓷基材的影响, 结果表明MoO3在这个玻璃陶瓷体系中的固溶度仅为1 wt.%，需要进一步优化体系组分。探讨了以Al3+、Fe3+和Nb5+作为电荷补偿离子时，稀土离子在钙钛锆石晶体中的取代机制，并研究其中的相变机制。揭示了不同价态的电荷补偿离子对稀土离子取代机制的异同以及不同钙钛锆石结构类型之间的相变机理。研究了不同钙钛锆石结构类型（2M、3O和4M）分别在不同剂量的Ne4+和Xe10+离子辐照下，这些结构的短程序和长程序的演变情况，指出4M结构具有更好的抗辐照性能。相关研究成果可为玻璃陶瓷基材固化高放核废提供工程基础和理论依据，为高放核废的最终处理安全处置奠定前期技术基础。