自蔓延高温合成钙钛锆石及其固化模拟锕系核素研究

The disposal of high-level radioactive waste(HLW) is a complex and technological problem in the processing of radioactive wastes around the world. Synroc, which has been considered as the waste form of second generation, is suggested as the potential immobilization material for HLW as it exhibits high chemical, thermal and radiation stability. Nuclide atoms can be fixed in the crystal lattice of synroc structure and the eventual security can be guaranteed. One synroc mineral, zirconolite, is chosen as the waste form of long-lived actinide nuclides in this project. Self-propagating high-temperature synthesis(SHS) is utilized as the preparation route. With the combination of quick press and optimization of processing parameters, zirconolite based mineral-like waste form with excellent properties will be prepared. Oxides of Nd and Ce will be added as the simulated elements of trivalent and tetravalent actinide nuclides in the synthesis procedure. Zirconolite based solidified body will be synthesized with immobilization of the simulated elements. Mode of occurrence, immobilizing mechanism and ultimate capacity of the simulated elements in zirconolite based waste form will be studied. The mechanical property and chemical stability will be characterized as well. This research will be a direction for the preparation of zirconolite based solidified body from SHS process. This project will also provide technological support for the immobilization of actinide nuclides by synroc process and their eventual disposal with prolonged security.

高放废物(HLW)是国内外放射性废物处理的重点和难点，人造岩石能够将核素原子固定于其晶格结构中，是较为理想的HLW固化介质。本课题拟选用人造岩石中稳定性高的钙钛锆石矿相，作为长寿命锕系HLW的固化基材，采用反应温度高、速度快、操作简便的自蔓延高温合成(SHS)技术，同时结合快速加压工艺，制备性能优异的钙钛锆石基人造岩石固化基材；添加Nd和Ce的氧化物模拟三价和四价锕系核素，制备包容模拟核素的钙钛锆石固化体；研究模拟锕系核素在钙钛锆石中的赋存状态及固化机制，探明固化体对不同模拟元素的极限包容量，并测定其机械性能和化学稳定性。本研究有望为SHS制备钙钛锆石固化基材提供依据，为简化人造岩石的制备工艺、推动锕系HLW的人造岩石固化和最终安全处置提供技术支持。

高放废物(HLW)是国内外放射性废物处理的重点和难点，人造岩石(Synroc)作为第二代HLW固化介质，能够将核素原子固溶于矿石的晶相结构中，是当前较为理想的HLW固化处理途径。本项目采用反应温度高、速度快、操作简便的自蔓延高温合成(SHS)技术，同时结合快速加压(QP)工艺，选取Fe2O3、CrO3、Ca(NO3)2、CuO、MoO3作为氧化剂，Ti粉作为还原剂，制备综合性能优良的钙钛锆石基人造岩石固化基材。添加Nd2O3和CeO2模拟三价和四价锕系核素氧化物，设计Ce取代钙钛锆石的Zr位，Nd同时取代钙钛锆石的Ca位和Zr位，SHS实验表明二者均能以固溶方式进入固化体矿相的晶格结构中。MCC-1浸出测试表明Ce和Nd具有较高的水热稳定性，其归一化浸出率在在Ca(NO3)2和CuO体系中较低，均为10-6～10-5 g m-2 d-1数量级，而在MoO3体系中达到10-2 g m-2 d-1数量级。通过本项目研究，验证了SHS工艺制备钙钛锆石型人造岩石的可行性，可以通过多个氧化物体系制备富钙钛锆石型人造岩石，模拟锕系核素能够以晶格固溶方式得到有效固化，且固化体的化学稳定性较高，包容量较大。本项目的顺利完成，为SHS制备钙钛锆石型人造岩石固化体提供依据，为简化人造岩石的制备工艺、推动锕系HLW人造岩石固化和最终安全处置提供技术支持。