燃烧反应制备Y2-xGdxTi2O7 烧绿石及其作为核废物固化材料的稳定性研究

Combustion reaction synthesis of Y2-xGdxTi2O7 pyrochlores and its aqueous durability as nuclear waste mateiral

摘要:

烧绿石基陶瓷材料是理想的核废物固化基材,本研究采用燃烧反应结合快速加压工艺,以CuO 为氧化剂、Ti为还原剂,在5分钟内快速制备出烧绿石基 Y_2-xGd_xTi₂O₇/Cu复合材料固化体。以Gd作为三价锕系核素的模拟物,设计Gd取代Y_2-xGd_xTi₂O₇烧绿石中的Y位。研究结果表明,Gd能完全取代Y位形成Gd₂Ti₂O₇ 烧绿石,所得产物没有杂质相的出现,且在烧绿石基体中没有出现相分离现象。选择Gd1.0样品进行浸出实验,结果表明该样品具有优异的水热稳定性,Cu, Y 和 Gd 元素的42天归一化浸出率分别低至 2.4×10^_-2, 1.1×10^_-5和5.3×10^_-6 g?m^_-2?d^_-1。

关键词:燃烧反应制备;核废物;烧绿石;化学稳定性

Abstract:

Pyrochlore-based ceramic is recognized as promising nuclear waste matrice. In this study, pyrochlore-based Y_2-xGd_xTi₂O₇/Cu composite waste forms were rapidly prepared within 5 minutes by combustion reaction plus quick pressing (CR/QP) synthesis route, where CuO was utilized as the oxidant and Ti as the reductant. As the surrogate of trivalent actinide nuclides, Gd was introduced to substitute the Y site with nominal formulation of Y_2-xGd_xTi₂O₇. The results demonstrate that Gd can totally replace the Y site and Gd₂Ti₂O₇ pyrochlore can be readily synthesized. There is no impurity phase generated in the products, and phase separation is not detected in the pyrochlore matrix. The selected Gd_1.0 waste form exhibits promising aqueous durability as the 42 days normalized leaching rates of Cu, Y and Gd elements are evaluated as low as 2.4×10^_-2, 1.1×10^_-5 and 5.3×10^_-6 g.m^_-2.d^_-1.

Key words:Combustion;reaction synthesis, Nuclear;waste, Pyrochlore, Chemical;durability.