Phase evolution and chemical durability of co-doped Gd2Zr2O7 ceramics for nuclear waste forms

Abstract (Gd 1− x Nd x ) 2 (Zr 1− x Ce x ) 2 O 7 (0≤ x ≤1.0) ceramics were synthesized to investigate the co-doping effects on the phase evolution and chemical durability of Gd 2 Zr 2 O 7 based nuclear waste forms. The phase structures of these solid solutions were identified by X-ray diffraction and their chemical durability was evaluated by static leach test (Materials Characterization Center, MCC-1). The results show that the Gd 2 Zr 2 O 7 ceramic adopts a pyrochlore structure while the co-doped (Gd 1− x Nd x ) 2 (Zr 1− x Ce x ) 2 O 7 (0.2≤ x ≤1.0) compositions exhibit a defect fluorite structure. Moreover, the normalized release rates of each element in (Gd 1− x Nd x ) 2 (Zr 1− x Ce x ) 2 O 7 (0≤ x ≤1.0) waste forms increase with the growing temperature and converge to constant values with enhanced leaching time. In the discussed time range (42 days), all the considered elements show a normalized release rate lower than 10 −4 g m −2 d −1 . Gd shows the highest normalized release rate of all the involved elements, while Zr shows the best chemical durability.