独居石陶瓷固化模拟次锕系核素及其稳定性研究

Due to the long half-lives and high toxicity of minor actinides (Np, Am, Cm), the safe immobilization and disposition of them is of great significance to the development of economic, safe and clean nuclear energy. In this project, monazite solid solutions doped simulated minor actinides(Pr, Eu, Gd) will be synthesized by solid state reaction using cerous oxalate, praseodymium oxide, europium oxalate, gadolinium oxalate, and ammonium dihydrogen phosphate as raw materials. Monazite ceramic waste forms will also be prepared by hot pressing (HP). The processing techniques of the simulated minor actinides-doped monazite solid solutions and waste forms will be optimized. The occurrence of the simulated minor actinides in the monazite ceramic waste forms will be studied. The chemical durability of the waste forms in deep geologic environment and the leaching rule of the nuclides will also be revealed. Moreover, the irradiation stability of monazite will be evaluated by theoretical calculations, and the long-term safety of the monazite ceramic waste forms will be predicted. The preparation techniques used in this project are practical and convenient. The heat treatment can be carried out at low temperatures. It is expected that the waste forms possess high purity crystalline phase and excellent performances, and the processing techniques facilitate their remote operation of engineering application. The research results can provide theoretical basis and technical support for the optimization and preparation of high-performance minor actinides waste forms.

次锕系核素(Np、Am、Cm)的毒性大，半衰期长，其安全的固化处理与处置，对实现核能发展的经济性、安全性和洁净性具有重要的意义。项目拟以草酸铈、氧化镨、草酸铕、草酸钆、磷酸二氢铵等为原料，利用固相反应合成模拟次锕系核素（Pr、Eu、Gd）独居石固溶体，采用热压烧结制备独居石陶瓷固化体，优化集成制备模拟次锕系核素独居石固溶体及其固化体的工艺技术，获得模拟次锕系核素在独居石陶瓷固化体中赋存状态的规律性认识，揭示固化体在深地质处置环境中的稳定性及其核素浸出规律，通过理论计算评价独居石固化材料的抗辐照稳定性，预测独居石陶瓷固化体的长期安全性。项目的工艺技术简洁实用，热处理温度低，预期固化体的目标矿物纯度高，性能优异，其工艺技术有利于陶瓷固化高放废物工程化应用的遥控操作，相关研究成果可为优化和制备高性能次锕系核素固化体提供理论依据和技术支持。

针对次锕系核素(Np、Am、Cm)的安全固化处理，项目以Ce2(C2O4)3.10H2O、Pr6O11 / Eu2O3 / Gd2O3、NH4H2PO4为原料，分别用稀土元素Pr、Eu、Gd来模拟Np、Am、Cm，通过固相反应和热压烧结制备独居石Ce1-xLnxPO4 (Ln=Pr, Eu, Gd)固溶体及其固化体，优化集成了单相、连续独居石Ce1-xLnxPO4 (x=0-1)固溶体及其固化体的制备技术，揭示了铈独居石固化体的组成-工艺-结构-性能的关系，获得了模拟次锕系核素（Pr、Eu、Gd）与铈独居石相互作用的规律性认识。利用水热反应釜来模拟固化体的深地质处置环境，研究热-水-力-化学（THMC）耦合作用下（pH=3-11，T=90-200℃，P=0.101-1.554 MPa）铈独居石固化体的化学稳定性、相稳定性、机械稳定性、蚀变机制等，在THMC耦合作用(90-200℃，0.101-1.554MPa， pH=5-9)下铈独居石固化体呈现出良好的稳定性，获得了THM耦合作用(温度)、HC耦合作用 (pH值)、烧结方式对固化体稳定性及蚀变机制影响的规律性认识，揭示了独居石陶瓷固化体在模拟深地质处置环境中的稳定性及其核素浸出行为。利用第一性原理和分子动力学，采用SIESTA、CASTEP、VASP、VASP-CASTEP组合等软件，对铈独居石的结构稳定性进行了初步研究，铈独居石具有很强的结构缺陷自修复能力，且只有在高能量粒子碰撞作用下才能形成空位和弗伦克尔缺陷。项目的工艺技术简洁实用，热处理温度低，固化体的目标矿物纯度高，性能优异，其工艺技术较容易实现高放废物固化处理的遥控操作，为优化和制备高性能次锕系核素铈独居石固化体提供了实验数据、理论依据和技术支持，对铈独居石陶瓷安全固化处理（次）锕系高放废物，实现核科学与技术的可持续发展具有重要的意义。