模拟次锕系核素在氟磷灰石陶瓷固化体中的赋存状态及其稳定性

The borosilicate glass waste forms for the immobilization of high level radioactive waste (HLW) have several shortcomings, such as the low solubility of phosphorus and minor actinides (Np, Am, Cm), poor thermodynamic stability. The project intends to prepare the fluorapatite ceramic waste forms doped with the simulated minor actinides (Sm, Eu, Gd) by the hot pressing sintering process. In addition, the project will optimize and integrate the preparation technologies of the fluorapatite ceramic waste forms. The relationships among the charge compensation mechanism, doping content of simulated minor actinides, hot pressing sintering process, crystal phase composition, microstructure and physical properties of the fluorapatite ceramic waste forms will be investigated. The occurrence and occupying mechanism of the simulated minor actinides (Sm, Eu, Gd) in the fluorapatite ceramic waste forms will be ascertained. The chemical durability and simulated minor actinide leaching behavior of the fluorapatite ceramic waste forms under the thermal-hydrodynamic-mechanical-chemical (THMC) coupling effects will be revealed. The preparation technologies used in the project are simple and practical. The sintering can be carried out at a lower temperature. It is expected that the fluorapatite ceramic waste forms with superior performance will be obtained. The preparation technologies would help to realize the resource utilization of the phosphorus containing HLW, and the engineering application of the HLW immobilization treatment. The related research results can provide the theoretical basis and technical support for the optimization and preparation of high-performance phosphorus and minor actinides containing HLW ceramic waste forms, and lay a solid foundation for promoting the applied basic research and safe disposal of HLW immobilization using the ceramic.

针对高放废物硼硅酸盐玻璃固化体存在磷和次锕系核素（Np、Am、Cm）溶解度较低、热力学稳定性较差等不足，本项目拟采用热压烧结工艺制备模拟次锕系核素（Sm、Eu、Gd）氟磷灰石陶瓷固化体，优化集成固化体制备工艺技术。系统研究电荷补偿机制、模拟次锕系核素掺量、热压烧结工艺与氟磷灰石陶瓷固化体晶相组成、显微结构和物理性能的关系，探明模拟次锕系核素（Sm、Eu、Gd）在氟磷灰石陶瓷固化体中的赋存状态和占位机制，揭示氟磷灰石陶瓷固化体在“热、水、力、化学”（THMC）耦合作用下的化学稳定性及其核素浸出行为。本项目工艺技术简洁实用，烧结温度较低，预期可获得性能优良的氟磷灰石陶瓷固化体，其工艺技术有利于实现含磷高放废物的资源化利用及其固化处理的工程化应用。相关研究成果可为优化和制备高性能含磷次锕系高放废物陶瓷固化体提供理论依据和技术支持，为推进高放废物陶瓷固化的应用基础研究及其安全处置奠定基础。

针对高放废物硼硅酸盐玻璃固化体存在磷和次锕系核素（Np、Am、Cm）溶解度较低、热力学稳定性较差等不足，本项目以Ca2P2O7、CaF2、Sm2O3、Eu2O3、Gd2O3、Na2CO3、SiO2等为原料，采用稀土元素Sm、Eu、Gd分别模拟Np、Am、Cm，通过固相反应和热压烧结制备固化基材纯氟磷灰石、掺模拟次锕系核素（Sm、Eu、Gd）氟磷灰石固溶体及其陶瓷固化体，优化集成了固化体制备技术，研究了氟磷灰石陶瓷固化体的组成-结构-工艺-性能的关系，揭示了模拟次锕系核素（Sm、Eu、Gd）在氟磷灰石中的赋存状态和占位机制，探明了氟磷灰石陶瓷固化体在模拟深地质处置环境中的的化学稳定性及其核素浸出行为。研究结果表明，在正电荷补偿机制和较低温度下成功实现了氟磷灰石陶瓷固化体的热压烧结制备；模拟次锕系核素在氟磷灰石中的赋存状态是一种类质同象状态，模拟次锕系核素（Sm、Eu、Gd）在氟磷灰石中的极限固溶量为1.2化学式单位，深入揭示了模拟次锕系核素在氟磷灰石Ca(1)位和Ca(2)位的优先占位倾向和占有率。在THMC耦合作用下（T=90-200℃，P=0.101-1.554MPa，pH=3-11）氟磷灰石陶瓷固化体呈现出优良的化学稳定性，模拟次锕系核素（Sm、Eu、Gd）归一化浸出率分别低至1.07×10-6（Sm）、5.22×10-7（Eu）、5.14×10-7（Gd） g•m-2•d-1，上述模拟次锕系核素（Sm、Eu、Gd）归一化浸出率比硼硅酸盐玻璃固化体中核素归一化浸出率（10-3 g•m-2•d-1）低3-4个数量级。本项目工艺技术简洁实用，烧结温度较低，固化体目标矿相的致密度和纯度高、浸出率低、化学稳定性优良，其工艺技术有利于实现含磷高放废物的资源化利用及其固化处理的工程化应用。相关研究成果可为优化和制备高性能含磷次锕系高放废物陶瓷固化体提供理论依据和技术支持，为推进高放废物陶瓷固化的应用基础研究及其安全处置奠定基础。