晶界对离子辐照下纳米Gd2Zr2O7损伤行为的影响机制

The internal microstructures, especially grain boundaries, have significant impacts on radiation damage and radiation stability of ceramic materials. The enhanced or restrained radiation resistance effects of grain boundary in many materials with nano-structure has been reported. The effects are spically important on a form of synthetic rock, SYNROC, which is composed of mutually compatible phases and possess crystal structures identical to chemical durable minerals and was proposed as the most promising host phases for immobilization of actinides and fission products. Gd2Zr2O7 with pyrochlore structure, which is chemical durable, radiation resistant(critical amorphization dose is higher than 100dpa), and have high tolerance of nuclear waste, is one of its candidate component phase. Currently, many studies focus mainly on using ion irradiation under accelerator or TEM to simulate the self-irradiation of the solidified radioactive nuclear waste elements to study the radiation damage in host phases and assess its safety, but no studies reported for Gd2Zr2O7 nanoceramic. On the basis of the synthesized Gd2Zr2O7 nanoceramic by SPS method and Ultrahigh pressure and low temperature sintering method, we would carry out the He2+ irradiation experiments to study the swelling, generation and accumulation of the defects, and phase transformation induced by irradiation. A grain boundary design for enhanced irradiation resistance will be proposed in our study to provide theoretical and technical foundation for the security of nuclear waste geological disposal.

作为材料中晶粒与晶粒的连接区域，晶界在辐照损伤行为中起着至关重要的作用，而目前晶粒减小(晶界面积增加)对抗辐照加固或减弱行为仍存在较大分歧。在对核废物最佳地质处置方式的人造岩石(陶瓷)晶格固化研究中，Gd2Zr2O7由于对高放锕系元素或后处理后核废物的高包容性、高耐辐照性能(>100dpa下未发生非晶化)和高化学稳定性是最佳优选材料体系。目前研究重点主要集中于采用强离子加速辐照来探知入射离子造成材料内的各辐照损伤行为，从而对固化核素自发衰变所致固化体的辐照损伤和安全性评估，然而晶界对纳米Gd2Zr2O7辐照损伤行为的影响还未开展相关研究。本项目基于前期采用SPS和UHPLT方法获得的纳米Gd2Zr2O7，拟采用He2+辐照，研究晶界对辐照致相变、辐照致缺陷的产生和聚集、辐照致肿胀等损伤行为的影响规律和机制。在此基础上提出抗辐照加固晶界设计方案，为核废物地质处置的安全性提供理论和技术基础。

作为材料中晶粒与晶粒的连接区域，晶界在辐照损伤行为中起着至关重要的作用，而目前晶粒减小(晶界面积增加)对抗辐照加固或减弱行为仍存在较大分歧。在对核废物最佳地质处置方式的人造岩石(陶瓷)晶格固化研究中，Gd2Zr2O7由于对高放锕系元素或后处理后核废物的高包容性、高耐辐照性能(>100dpa下未发生非晶化)和高化学稳定性是最佳优选材料体系。目前研究重点主要集中于采用强离子加速辐照来探知入射离子造成材料内的各辐照损伤行为，从而对固化核素自发衰变所致固化体的辐照损伤和安全性评估，然而晶界对纳米Gd2Zr2O7辐照损伤行为的影响还未开展相关研究。本项目基于前期采用放电等离子体烧结（SPS），超高压烧结（UHPS）和两步烧结方法获得的纳米Gd2Zr2O7，采用不同剂量He+辐照，研究了晶界对辐照致非晶化、辐照致缺陷的产生和聚集、辐照致肿胀等损伤行为的影响规律和机制。结果表明，辐照后非晶化百分比、晶内空位缺陷团簇尺寸和密度、晶格膨胀、材料表明肿胀均随晶界面积的减小而增加，且提高晶界面积对各阶段的He泡形成和演化具有明显抑制作用。在此基础上提出了将固化体晶粒纳米化的微观结构设计方案来提升固化体的抗辐照性能。根据该方案，我们最终开展了易实现工业应用的微波烧结并成功制备出Gd2Zr2O7纳米陶瓷。该方法获得的纳米陶瓷不仅能够满足应用条件，而且方法简单，成本低，具有很光明的应用前景。本项目研究为核废物地质处置的安全性提供了学术和技术支持。