新型载高放核废核素纳米陶瓷固化体的体系设计与辐照稳定性研究

Gd2Zr2O7 was chosen as one of the most promising candidate components of ceramic wasteforms in the use of high-level-nuclear-waste-immobilizations on the basis of (a) the extremely high cross section of Gd for neutron absorption, which providescriticality safety, (b) high performance to resist radiation damage by energeticparticles, (c) high-capacity immobilization of high-level nuclear waste, and (d) chemical durable. Nevertheless, higher requirement is to put forward for the anti-radiation strengthen of the ceramic waste forms, owing to the amorphization and the swelling induced by radiation. According to the applicant’s research foundation on inter-discipline subject between nanoceramic and radiation effects, the applicant proposes these ideas. Due to the high self-healing capacity of defects in nanoceramics, radiation damage in the nanostructure significantly weakens. Moreover, the helium bubble aggregation that causes material swelling mostly occurs at the grain boundary, so the morphization and swelling in the nanostructure induced by irradiation are more impossible. Based on these results, we intend to design a system for the nanostructured Gd2Zr2O7 ceramic waste forms containing high-level nuclear elements. Through comprehensive irradiation simulation experiments, the study will obtain the mechanism and radiation stability of the radiation induced amorphization, volume swelling, mechanical properties and leaching rates in the Gd2Zr2O7 based ceramic wasteforms with nano grain size. A design of microstructure enhancing irradiation resistance and a low-cost synthetic method for Gd2Zr2O7 based ceramic wasteforms containing high-level nuclear waste will be proposed in our study to provide important scientific basis, date support and technical foundation for the security of nuclear waste geological disposal.

在高放核废核素的固化应用中，Gd2Zr2O7由于锕系核废固溶量大，抗辐照性能出色，化学稳定性好且可吸收中子而安全性高等优点成为理想的陶瓷固化基材。但是，辐照致非晶化、辐照肿胀等问题对陶瓷固化体的抗辐照加固提出了更高的要求。申请者基于其在纳米陶瓷和辐照效应交叉学科上的研究基础认为：纳米陶瓷具有结构自修复和缺陷自修复能力，辐照损伤在纳米结构中显著弱化，加之氦泡聚集引起的肿胀也多发生在纳米陶瓷的晶界处，因此使纳米结构很难非晶化和产生辐照肿胀。基于上述，本申请项目拟开展纳米结构的载模拟核素Gd2Zr2O7陶瓷固化体体系设计研究，并通过综合辐照模拟实验，获得晶粒纳米化对固化体辐照致非晶化，辐照肿胀，力学性能，浸出率等的影响规律和微观作用机制。在此基础上提出具有实用价值的载高放核废核素纳米陶瓷固化体的抗辐照加固微观结构设计方案，为其在先进核能系统中的应用提供重要的科学依据，数据支撑和技术支持。

在高放核废核素的固化应用中，Gd2Zr2O7由于锕系核废固溶量大，抗辐照性能出色，化学稳定性好且可吸收中子而安全性高等优点成为理想的陶瓷固化基材。但是，辐照致非晶化、辐照肿胀等问题对陶瓷固化体的抗辐照加固提出了更高的要求。本项目基于纳米陶瓷具有辐照缺陷结构自修复、辐照损伤在纳米结构中显著弱化使得纳米结构很难非晶化和产生辐照肿胀等在抗辐照方面的特殊优势，开展了纳米结构的载模拟核素Gd2Zr2O7陶瓷固化体体系设计研究，并通过综合辐照模拟实验，获得晶粒纳米化对固化体辐照致非晶化、辐照肿胀、力学性能和浸出率等的影响规律和微观作用机制。主要取得了六个方面的创新成果：一是研究发现Gd2Zr2O7纳米陶瓷固化体固化TRPO模拟核废可高达60 wt.%，远远高于粗晶陶瓷固化体45 wt.%最高固化能力，原因在于纳米结构中丰富的晶界提高了核素在固化体固溶的冗余度。二是研究发现纳米陶瓷固化体在He离子辐照模拟的α衰变实验中，纳米陶瓷固化体显示不易非晶化，在同等辐照剂量下，纳米样品显示出滞后于微米样品的He泡演化过程，呈现优异的抗辐照性能。三是研究发现在Kr离子辐照模拟α衰变反冲核实验中，纳米陶瓷固化体呈现出大Kr泡，而微米样品直接呈现出辐照损伤的最终形式——微裂纹，且纳米样品非晶化程度较微米样品更低。四是Nd与Ce共掺模拟核废Gd2Zr2O7纳米陶瓷固化体在He离子辐照模拟的α衰变实验中，微米样品微裂纹长度是纳米样品的4倍，且纳米样品微裂纹密度更低，说明纳米样品抗辐照性能更好。五是TRPO模拟核废纳米陶瓷固化体和Nd/Ce元素简化模拟核废的纳米陶瓷固化体均呈现出优于水泥固化体与玻璃固化体优异的抗浸出性能，浸出率低三个数量级，而辐照后，纳米样品浸出率几乎未发生变化而微米样品浸出率增加。六是探究并获得了高放核废处置的陶瓷固化整体解决方案（川大方案），即采用燃烧法完全提取高放核素形成粉体，不产生废液，而后干法成型并微波烧结形成高致密纳米陶瓷固化体。本研究提出具有实用价值的载高放核废核素纳米陶瓷固化体的整体设计方案，认识了纳米陶瓷固化体的辐照稳定性及其抗辐照机理，为载核素热态实验和未来核废料处置应用提供了学术和技术基础。