Leaching stability of simulated waste forms for immobilizing An³⁺ by Gd₂Zr₂O₇ with Nd³⁺

Abstract

In order to investigate the anti-leaching capability of pyrochlore Gd₂Zr₂O₇ immobilized An³⁺, trivalent neodymium was used as the simulacrums for radioactive wastes with trivalence, Gd_2−xNd _xZr₂O₇(0.0⩽x⩽2.0) series samples were successfully synthesized by high temperature solid reaction and using Gd₂O₃, ZrO₂ powders as starting materials. The experiments of long-term chemical stability were conducted in synthetic seawater at 40 and 70 °C. The XRD diffractive data and extraction ratio of as-received samples were collected with the help of X-ray diffraction (XRD) instrument and inductively coupled plasma mass spectrometry (ICP-Mass). The results indicate that the phases of as-received compounds keep the single phase of pyrochlore. The extraction ratio of Gd³⁺, Zr⁴⁺ and Nd³⁺ in waste forms is increasing with the increase of immersion time in synthetic seawater. The extraction ratio of waste forms at 70 °C is higher than at 40 °C. The highest extraction ratio of Gd³⁺, Zr⁴⁺ and Nd³⁺ after 42 days is near 0.025 8, 0.003 8 and 0.045 2 μg·mL⁻¹, respectively.

Keywords

pyrochlore / radioactive waste with trivalence / waste forms / anti-leaching capability

References

[1] Hatch L P Ultimate Disposal of Radioactive Wastes[J]. Amer. Sci., 1953, 41: 410-421.

[2] Ringwood A E, Kesson S E, Ware N G, . Immobilisation of High Level Nuclear Reactor Wastes in SYNROC[J]. Nature, 1979, 278: 219-223.

[3] Ewing R C, Weber W J, Lian J Nuclear Waste Disposal-pyrochlore (A₂B₂O₇): Nuclear Waste Form for the Immobilization of Plutonium and “Minor” Actinides[J]. J. Appl. Phys., 2004, 95: 5 949-5 971.

[4] Yndinsev S V, Lukinykh A N, Tomilin A A, . Alpha-decay Induced Amorphization of Cm-doped Gd₂Ti₂O₇ [J]. J. Nucl. Mater., 2009, 385: 200-203.

[5] Lang M, Zhang F X, Zhang J, . Review of A₂B₂O₇ Pyrochlore Response to Irradiation and Press [J]. Nuclear Instruments and Method in Physics Research B, 2010, 268: 2 951-2 959.

[6] Montel J M Mineral and Design of New Waste Forms for Conditioning Nuclear waste [J]. Comptes Rendus Geoscience, 2011, 343: 230-236.

[7] Wang J W, Zhang F X, Lian J, . Energetics and Concentration of Defects in Gd₂Ti₂O₇ and Gd₂Zr₂O₇ Pyrochlore st High Press [J]. Acta Materialia, 2011, 59: 1 607-1 618.

[8] Mandal B P, Grag N, Sharma S M, . Solubility of ThO₂ in Gd₂Zr₂O₇ Pyrochlore: XRD, SEM and Raman Spectroscopc Studies[J]. J. Nucl. Mater., 2009, 392: 95-99.

[9] Wang S X, Begg B D, Wang L M, . Radiation Stability of Gadolinium Zirconate: A Waste Form for Plutonium Disposal [J]. J. Mater. Res., 1999, 14: 4 470-4 473.

[10] Weber W J, Ewing R C Plutonium Immobilization and Radiation Effects[J]. Science, 2000, 289: 2 051-2 052.

[11] Zhu X Z, Luo S G, Wang D X Synroc for Actinides Immobilization [J]. Chinese Journal of Nuclear Science and Engineering, 1997, 17(2): 173-174.

[12] Yang J W, Luo S G, Li B J, . Pyrochlore-rich Synroc for Immobilization of Actinides [J]. Atomic Energy Science and Technology, 2001, 35: 104-108.

[13] Zhang H, Yang J W, Li B J, . Study on Leaching Behaviors of Pyrochlore-rich Synroc Under Simulated Disposal Conditions [J]. Journal of Nuclear and Radiochemistry, 2004, 26(2): 65-67.

[14] Lu X R, Dong F Q, Hu S, . Phase and Chemical Stability of Simulated Waste Forms Gd₂Zr_2−xCe_xO₇(0⩽x⩽2.0) [J]. Acta Phys. Sin., 2012, 61(15): 152 401