高放核废料纳米陶瓷固化体的辐照自修复行为研究

ceramic solidification becomes a candidate solution for resolving high-level radioactive nuclear waste disposal and storage gradually，and candidate materials those have a high ability of anti-radiation have been selected. Nevertheless, amorphization, phase transition, and swelling induced by radiation are still fatal problems in application. According to the applicant’s research foundation on inter-discipline subject between nanoceramic and radiation effects, the applicant proposes these ideas. Due to high interfaces and high surface energy of nanoceramic, the energy deposition of irradiated alpha particle at the grain boundary shows great probability. So the effect of radiation on the amorphization of grain in nanoceramics is relatively weaker compared with traditional ceramics. Meanwhile, as helium bubble aggregation that causes material swelling mostly occurs at the grain boundary, radiation damage in the nanoceramic significantly weakens. All of these will lead to a completely different radiation effects under the nuclear waste irradiation between nanoceramics and traditional ceramics (grain size is in micron level). Even irradiation will effectively enhance the self-organization and self-healing capacity of defects in nanocrystals because of heating effects caused by β-decay. This application project will focus on three most important nuclear waste host nanoceramic materials. Through comprehensive irradiation simulation experiments, the study will obtain the mechanism of amorphization and swelling induced by α-particle irradiation, and explore the mechanism of self-healing problem of recrystallization caused by β-ray irradiation. On the basis of the effect of composite damage experiments ( the coupling effect of the displacement effect, helium effect and heating effect ), this project will select nanoceramic of high resistance to radiation. The investigation will lay the academic and technical foundation for nuclide hot experiments and future nuclear waste disposal applications.

陶瓷固化逐步成为解决高放核废料处置和存储的候选方案，被遴选出了几种抗辐照能力强的候选材料，但辐照非晶化、辐照相变和肿胀等依然是其应用中的致命问题。而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，认为纳米陶瓷晶界多、界面能高，辐照α粒子能量沉积在晶界处的几率大，对晶粒本身辐照非晶化影响相对较小，氦泡聚集引起的材料肿胀也多发生在晶界处，辐照损伤在纳米陶瓷中显著弱化，导致纳米陶瓷和传统陶瓷在辐照下具有完全不同的效应，加上β衰变引起的热效应，甚至会有效增强其中缺陷的自组织和自修复能力。本申请项目重点研究三种当前最重要的核废料固化用纳米陶瓷，通过综合辐照模拟实验，获得α衰变致非晶化、肿胀的机制，探索β衰变引起再结晶的“自我修复”的机理，根据复合损伤效应实验（移位效应、氦效应和热效应的耦合效应），遴选出自我修复能力强的高抗辐照纳米陶瓷，为热态实验和未来核废料处置应用奠定学术和技术基础。

陶瓷固化逐步成为解决高放核废料处置和存储的候选方案，国际上遴选出了几种抗辐照能力强的候选材料，但辐照非晶化、辐照相变和肿胀等依然是其应用中的致命问题。本项目提出了纳米陶瓷固化体来解决以上问题，主要是基于：纳米陶瓷中可以作为辐照缺陷吸收“陷阱”的晶界面积大，对晶粒本身辐照非晶化影响相对较小；氦泡聚集引起的材料肿胀多发生在晶界处，肿胀在纳米结构固化体中显著弱化；间隙原子型点缺陷扩散到晶界处后甚至会反扩散回晶粒内部和空位点缺陷复合，从而使纳米结构具备更强的辐照缺陷自修复能力；β衰变引起的电离激发效应和热效应，也会有效增强固化体的晶体结构自修复能力。本项目主要研究内容是从三种当前最重要的核废料固化中遴选出高放核废固溶量大，抗辐照性能出色的Gd2Zr2O7，合成纳米结构陶瓷，通过综合辐照（α，β，Kr+）实验，模拟研究纳米结构固化体在α衰变离子作用下的微观结构和缺陷变化（如相变或非晶化、间隙点缺陷团、空位聚集形成的空洞、辐照肿胀等）及其与晶粒尺寸的关系，并探索β衰变引起再结晶的“结构自修复”机理，提出抗辐照的晶界优化设计方案。研究结果表明纳米结构相比微米结构具有更好的缺陷自修复和结构自修复能力，且晶粒尺寸存在优选范围（约48nm），本研究也首次获得了易于工业化生产的纳米陶瓷烧结烧结技术。以上结果对于预测核废料固化中可能发生的辐照损伤现象具有现实意义，为载核素热态实验和未来核废料处置应用奠定了学术和技术基础。所以本研究不仅具有学术意义，也具有潜在应用价值。