Effect of Decay-daughter on An₂Zr₂O₇ Simulated Immobilization Structure by Lanthanide and γ-ray Irradiation Resistance

The zirconate pyrochlore is regarded as candidate crystalline matrix to immobilize actinide elements because of its chemistry and radiation stability. The decay daughters from α-decay of the incorporated actinides can affect the immobilization structure and properties. Due to similarities in charge, size and chemical properties, Nd and La were used as surrogated elements for parent elements (Pu and Am) and daughter elements (U and Np), respectively. The zirconate pyrochlores (La_xNd_1-x)₂Zr₂O₇ were prepared by the sol-gel method. These samples were irradiated by ⁶⁰Co γ-ray source with 233.78 kGy dose. The X-ray diffraction, Raman spectroscopy and structure refinement were employed to investigate the structure evolution. The results show that pyrochlores in the(La_xNd_1-x)₂Zr₂O₇ system are single pyrochlore structure. The lattice parameters increase gradually and the degree order of pyrochlore structure increases with the La content. The analysis of the irradiation experiment suggests that the An—O.48f bond length increases with the decay-daughters content, and the irradiation resistance of pyrochlore immobilization decreases.