GdEuZrCeO_(7)烧绿石陶瓷核废物固化体的制备及化学稳定性

Preparation and Chemical Stability of GdEuZrCeO_(7) Pyrochlore Ceramic Nuclear Waste Forms

选择镧系元素Eu、Ce分别模拟高放废物中的三价和四价锕系核素,以硝酸盐和氧化物为原料,分别采用普通烧结法和液相烧结法制备了GdEuZrCeO_(7)烧绿石陶瓷核废物固化体。利用XRD、SEM-EDS对固化体的物相组成、微观结构和化学组成进行了测试表征,研究了烧结方法、烧结温度和烧结助剂对固化体物相组成、晶粒大小以及致密性的影响,并采用PCT静态浸出法研究了固化体的化学稳定性。结果表明:GdEuZrCeO_(7)烧绿石陶瓷固化体的物相结构为无序缺陷萤石型结构;较高的烧结温度有利于固化体结晶度和致密性的提高,液相烧结和添加烧结助剂对固化体致密性的提高并不明显;PCT结果说明固化体具有较好的化学稳定性,元素的归一化浸出率总体处于10^(-7)~10^(-4) g·m^(-2)·d^(-1)范围。

In this work, the lanthanide of Eu and Ce were used as the surrogates for the trivalent and tetravalent actinide nuclides in high-level radioactive waste. GdEuZrCeO_(7) pyrochlore ceramic nuclear waste forms were prepared by ordinary sintering method and liquid phase sintering method using nitrates and oxides as raw materials. The phase composition, microstructure and chemical composition of the waste form were analyzed and characterized by XRD and SEM-EDS techniques. The influences of sintering methods, sintering temperature and sintering aids on the phase composition, grain size and densification were investigated. And the chemical stability of the waste forms was evaluated by PCT static leaching method. The results showed that the phase structure of the GdEuZrCeO_(7) pyrochlore ceramic waste form is the disordered defect-fluorite structure. Higher sintering temperature is beneficial to the improvement of the phase crystallinity and densification of the waste forms. Liquid phase sintering and adding sintering aids can’t improve the densification of the waste form significantly. PCT results indicated that the waste forms had good chemical stability and the elemental normalized leaching rate was generally in the range of 10^(-7)~10^(-4) g·m^(-2)·d^(-1).