高放废物地质处置用玻璃固化体的辐射坚稳性研究与评估

This proposal focus on the 20th direction of the 2018 Introduction of NSFC and CNNC, will investigate the stability of solidified form of high level radioactive waste (HLW) for geological disposal. Glass solidification is used for treat the HLW in China. Therefore, the stability of the solidified glass in the radiation field is crucial to the research and development of the HLW disposal technology. Due to the specificity of the HLW source to be treated, it is necessary to systematically study the stability of the specific glass and the migratory behavior of the radionuclide in the solidified glass. In this project, ion/electron irradiation will be used to simulate α, α recoils, β and γ decay in the HLW. The modifications in the microstructures and macro-properties of glass waste form induced by ion/electron irradiation will be investigated. Based on these experimental results, the evaluation methodology of the robustness of glass waste form could be obtained. By measuring the specified nuclide, the influence of the radiation damages on the migratory and leaching behavior of radionuclides in the glass waste form will be studied. Combining with the computer simulation, the evaluation methodology and standard of the robustness of glass waste form could be established. The topics in this proposal are the scientific problems related to the assessment of long-term irradiation stability of glass waste forms, which are the urgent and original works on this specified glass. The expected results can provide the key basic data and important scientific basis for the research and development of the glass solidification technology of HLW. The project team is a lean research team. It has been long engaged in research on the radiation effects of glass waste form. Dozens of related research papers have been published, and an international cooperation network has been established. It has the ability to undertake the research and train a group of professionals.

本项目针对《核技术创新联合基金2018年指南》方向20，拟围绕高放废物地质处置用固化体的坚稳性开展研究。玻璃固化是我国拟采用的技术路线。由于待处置的高放废物源项具有特异性，必须针对特定配方玻璃的坚稳性进行系统研究。其研究结果直接决定处置技术和工艺的可行性。本项目拟利用离子/电子束模拟高放废物中的α粒子、α反冲核、β及γ射线辐照，研究辐照导致玻璃材料微观结构和宏观性能的变化，评估玻璃材料的辐射损伤效应；同时测量特征核素，研究辐射损伤对固化体内核素迁移及浸出行为的影响；然后，结合计算机理论模拟，建立混合辐射场中玻璃固化体坚稳性评价方法和标准。本项目研究具有紧迫性，相关工作具有原创性。研究结果可为化解高放废液玻璃固化技术难题提供关键基础数据和科学依据。项目组人员结构合理，并长期从事玻璃固化体辐照效应研究，已发表数十篇相关论文，且拥有广泛的国际合作网络，有能力承担该项研究，并培养一批专门人才。

固化体的辐射坚稳性是影响高放废物成功处置的关键因素之一。硼硅酸盐玻璃因制备工艺成熟、对放射性废物包容量大、化学稳定性高等优点，是高放废物固化体的优选基材。本项目分别利用了载能离子，电子和伽马射线模拟放射性核素衰变强辐射场，结合拉曼光谱、红外光谱、扫描电子显微镜、电感耦合等离子发射光谱、分子动力学模拟等对玻璃固化体的力学性能、体积/密度、微观结构和特征元素浸出率开展了系统研究。研究结果表明：.在模拟α衰变场中，玻璃的硬度和模量随辐照剂量的增加表现出先快速下降而后饱和的趋势，且饱和变化量无明显的组分相关性。饱和剂量约为0.1 dpa，硬度和模量的饱和变化量分别为–35%和约–18%。核能量沉积是α衰变场中玻璃力学性能变化的主要原因。放射性核素的β和γ衰变也能导致玻璃的力学性能发生显著变化，且变化量具有明显的组分相关性。辐照还导致了玻璃的体积/密度发生不超过6%的变化，且变化量与玻璃组分密切相关。通过对辐照样品微观结构的实验表征和分子动力学模拟发现，上述宏观物性变化与辐照缺陷的产生、硅原子网络聚合度的降低等因素，特别是硼原子平均配位数的降低有关。辐照能够加速模拟地下水环境中玻璃固化体的腐蚀速率。在浸出反应初期，特征元素的初始浸出率均有不同程度的增加，长期浸出实验结果则显示浸出率随时间的增加逐渐趋于饱和。浸出率的增加主要与微裂纹的产生、玻璃网络体聚合度的降低有关，而表面富Si胶体层的存在能有效抑制玻璃与水的接触，使得特征元素的浸出速率降低。结合上述研究结果和文献调研，我们主要从硬度和初始浸出率的角度提出了玻璃固化体坚稳性的评估方法和建议。并利用分子动力学编写了具有自主知识产权的模拟软件，可对特定的玻璃和源项组合给出预期寿命。.依托基金资助和以上研究工作，课题组培养研究生32名，发表各类学术论文29篇，并积极在国内外学术会议上分享研究进展。所取得的研究结果可为化解高放废液玻璃固化技术难题提供关键基础数据和科学依据。全面完成了计划书中的研究内容，实现了研究目标。