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Order-disorder structural tailoring and its effects on the chemical stability of (Gd, Nd)2(Zr, Ce)2O7 pyrochlore ceramic for nuclear waste forms

  • Wang, Yan (Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory, Southwest University of Science and Technology) ;
  • Wang, Jin (Fundamental Science on Nuclear Wastes and Environmental Safety Laboratory, Southwest University of Science and Technology) ;
  • Zhang, Xue (School of Materials Science and Engineering, Southwest University of Science and Technology) ;
  • Li, Nan (School of Materials Science and Engineering, Southwest University of Science and Technology) ;
  • Wang, Junxia (School of Materials Science and Engineering, Southwest University of Science and Technology) ;
  • Liang, Xiaofeng (Sichuan College of Traditional Chinese Medicine)
  • Received : 2021.11.29
  • Accepted : 2022.02.01
  • Published : 2022.07.25

Abstract

Series of unequal quantity Nd/Ce co-doped ceramic nuclear waste forms, (Gd, Nd)2(Zr, Ce)2O7, were prepared to tailor its ordered pyrochlore or disordered fluorite structure. The phase transition, microtopography, and elemental composition of the ceramic samples were systematically investigated, especially the effect of order-disorder structure on the chemical stability. It was confirmed that unequal quantity of Nd/Ce could synchronously replace the Gd/Zr-sites of Gd2Zr2O7. And the phase transition of order-disorder structure could be successfully tailored by regulating the average cationic radius ratio of (Gd, Nd)2(Zr, Ce)2O7 series. The elements of Gd, Nd, Zr, and Ce are uniformly distributed in the ordered or disordered structures. The MCC-1 leaching results showed that (Gd, Nd)2(Zr, Ce)2O7 pyrochlore ceramic nuclear waste forms had excellent chemical stability, whose elements' normalized leaching rates were as low as 10-4-10-7 g·m-2·d-1 after 7 days. In particular, the chemical stability of disordered structure was superior to that of ordered structure. It was proposed that the force constant and the closest packing were changed with the structure transformation resulting the chemical stability difference.

Keywords

Acknowledgement

We received a great deal of support and assistance from the National Natural Science Foundation of China (Nos. 12075195 and 11705153), the Foundation of Laboratory of National Defense Key Discipline for Nuclear Waste and Environmental Safety of Southwest University of Science and Technology (No. 17kfhk05).

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