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

Abstract

Lanthanide-Borosilicate (LaBS) glass capable to dissolve up to ~10 wt.% PuO 2 is designed for immobilization of plutonium-bearing wastes. The sample of LaBS glass with a target chemical composition (wt %): 9.0 SrO was prepared from PuO 2 powder and mechanically activated mixture of chemicals at 1500 C. The obtained product was visually homogeneous. Xray diffraction of the as-prepared glass showed that it mostly consists of a vitreous phase with small amounts of crystalline PuO 2 (or PuO 2 -HfO 2 solid solution with minor HfO 2 ), britholite and an oxide with a fluorite structure and a composition close to GdHfO 1.75 . The crystalline fraction increased after storage for ~1 year. Magnitude of the FT of EXAFS spectrum at Pu L III edge shows that the peak due to first coordination sphere is much more intense than that of the second shell. This indicates that though some Pu entered crystalline phases (mainly distorted PuO 2 ), its major fraction remained in the vitreous phase. Fit of the spectrum (R-factor = 0.02) gives the following distances: R (Pu-O 1 ) 1 = 1.98 Ǻ ( = 0.04), R (Pu-O 1 ) 2 = 2.18 Ǻ ( = 0.04), R (Pu-O 1 ) 3 = 2.35 Ǻ, R (Pu-Pu) = 3.72 Ǻ ( = 0.04), R (Pu-O 2 ) = 4.4 Ǻ ( = 0.06). Oxygen environment of the Pu 4+ ions in the vitreous phase resembles axially squeezed tetragonal pyramid with a coordination number ~5. The distances ~2.35 Ǻ and ~4.4 Ǻ correspond to the pairs Pu-O in the first and the second shells in the crystalline PuO 2 . The distance ~3.72 Ǻ corresponds to the Pu-Pu and/or Pu-M (M = Ln, Hf) distances. EXAFS spectra of Hf show that Hf is present mostly in the vitreous phase with major neighbors at 2.17 and ~3.2 A.

Inorganic Waste Forms for Efficient Immobilization of Radionuclides

“…La atoms uniformly distributed in the glass structure without any clustering surrounded by about 6 nonbridging oxygen (O) atoms mixed with sodium (Na) and calcium (Ca) atoms to the impairment of the BO 4 groups. Additionally, because of their facile ionization behavior compared with those of lanthanides, various actinides (U, Pu, Np, Am, and Th) can be easily immobilized by conditioning borosilicate glasses. − …”

Plutonium Solubility in High-Level Waste Alkali Borosilicate Glass

“…Glass melts were made with a SB2/SB3 Slurry Mix Evaporator (SME) a simulant and SB6 SME simulant both using hafnium oxide as a PuO 2 surrogate. Testing has shown that HfO 2 is the best surrogate for PuO 2 in glasses from solubility and glass structure perspectives (Lopez, 2003;Shiryaev, 2009). The SB2/SB3 simulant was on hand and available for initial testing.…”