镧系元素模拟衰变子体对An_2Zr_2O_7固化体结构及其γ辐照性能的影响

锆基烧绿石An2Zr2O7以优异的抗辐照性能和化学稳定性成为高放废物中锕系核素的理想固化基材,高放废物固化体在长期贮存过程中不断衰变产生衰变子体,必将影响固化体的结构和性能。本文以镧系核素Nd模拟锕系核素Pu、Am,La模拟其衰变子体U、Np,通过溶胶凝胶方法合成了(LaxNd1-x)2Zr2O7模拟固化体。样品经高能γ辐照,辐照剂量为233.78kGy。利用X射线衍射、Raman振动光谱和结构精修方法对辐照前后的系列样品进行了分析。结果表明:(LaxNd1-x)2Zr2O7系列固化体均为单一的烧绿石结构相;固化体的晶格常数随La的增加呈线性增加,晶体结构趋于有序化,意味着衰变子体有助于固化体趋向于更加有序的烧绿石结构。γ辐照和结构精修结果表明,随着子体的增加,An—O48f键长增大,离子键结合力减小,在辐照情况下晶格易发生无序化,抗辐照能力减弱。

Effect of Decay-daughter onAn2Zr2O7 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.