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XAFS of Pu and Hf LIII Edge in Lanthanide-Borosilicate Glass

Published online by Cambridge University Press:  15 February 2011

A.A. Shiryaev
Affiliation:
Institute of Crystallography RAS, Leninskii pr. 59, Moscow 119333, Russia
Ya.V. Zubabichus
Affiliation:
RRC “Kurchatov Institute”, Kurchatov sq. 1, Moscow, Russia
S.V. Stefanovsky
Affiliation:
SIA Radon, 7 Rostovskii lane 2/14, Moscow 119121, Russia
A.G. Ptashkin
Affiliation:
SIA Radon, 7 Rostovskii lane 2/14, Moscow 119121, Russia
J.C. Marra
Affiliation:
Savannah River National Laboratory, Aiken 29808 SC, USA
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Abstract

Lanthanide-Borosilicate (LaBS) glass capable to dissolve up to ∼10 wt.% PuO2 is designed for immobilization of plutonium-bearing wastes. The sample of LaBS glass with a target chemical composition (wt %): 9.0 Al2O3, 11.8 B2O3, 12.2 Gd2O3, 6.3 HfO2, 17.2 La2O3, 13.6 Nd2O3, 9.5 PuO2, 18.1 SiO2, 2.3 SrO was prepared from PuO2 powder and mechanically activated mixture of chemicals at 1500 °C. The obtained product was visually homogeneous. Xraydiffraction of the as-prepared glass showed that it mostly consists of a vitreous phase withsmall amounts of crystalline PuO2 (or PuO2-HfO2 solid solution with minor HfO2), britholite andan oxide with a fluorite structure and a composition close to GdHfO1.75. The crystalline fractionincreased after storage for ∼1 year. Magnitude of the FT of EXAFS spectrum at Pu LIII edgeshows that the peak due to first coordination sphere is much more intense than that of the secondshell. This indicates that though some Pu entered crystalline phases (mainly distorted PuO2), itsmajor fraction remained in the vitreous phase. Fit of the spectrum (R-factor = 0.02) gives thefollowing distances: R (Pu-O1)1 = 1.98 (σ = 0.04), R (Pu-O1)2 = 2.18 (σ = 0.04), R (Pu-O1)3= 2.35, R (Pu-Pu) = 3.72 (σ = 0.04), R (Pu-O2) = 4.4 (σ = 0.06). Oxygen environment ofthe Pu4+ ions in the vitreous phase resembles axially squeezed tetragonal pyramid with acoordination number ∼5. The distances ∼2.35 and ∼4.4 correspond to the pairs Pu-O in thefirst and the second shells in the crystalline PuO2. The distance ∼3.72 corresponds to the Pu-Pu and/or Pu-M (M = Ln, Hf) distances. EXAFS spectra of Hf show that Hf is present mostly in thevitreous phase with major neighbors at 2.17 and ∼3.2 A.

Type
Research Article
Copyright
Copyright © Materials Research Society 2009

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