Tc and Re behavior in borosilicate waste glass vapor hydration tests II

Buechele, Andrew C.; McKeown, David A.; Lukens, Wayne W.; Shuh, David K.; Pegg, Ian L.

doi:10.1016/j.jnucmat.2012.05.032

Cited by 22 publications

(9 citation statements)

References 15 publications

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“…A key difference between 99 Tc and Re is that Tc 7+ is more easily reduced to Tc 4+ than is Re 7+ to Re 4+ . 3,10 In experiments with glasses of varying redox conditions comparing 99 Tc to Re, only Re 0 and Re 7+ but no Re 4+ or Re 6+ were observed, even though in comparable 99 Tc glasses Tc 0 , Tc 4+ , and Tc 7+ were observed. 11 Thus, it has been suggested that, at least in borosilicate LAW glasses, Re may not be a representative substitute for 99 Tc under reducing conditions.…”

Section: Technetium and Rheniummentioning

confidence: 99%

“…11 Additionally, in vapor hydration tests (VHTs 12 ), 99 Tc was always reduced to Tc 4+ regardless of the starting distributions of 99 Tc valence, whereas Re 7+ species were always dominant in the comparable Re glasses. 10,13 While 99 Tc is enriched at the outer corroded gel layer of amorphous silicate and almost absent at the center, Re concentrations are low near the surface of comparable samples and approach that of unreacted glass near the center.…”

Section: Technetium and Rheniummentioning

confidence: 99%

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Structure of Rhenium‐Containing Sodium Borosilicate Glass

Goel

McCloy

Windisch

et al. 2012

Int J of Appl Glass Sci

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A series of sodium borosilicate glasses were synthesized with KReO 4 or Re 2 O 7 , to 10,000 ppm (1 mass%) target Re, to assess effects of large concentrations of rhenium on glass structure and fto estimate solubility of 99 Tc, a radioactive component in low active waste nuclear glasses. Rhenium was used as a surrogate for 99 Tc for laboratory testing, due to similarities in chemistry, ionic size, and redox. Magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, and Raman spectroscopy were performed to characterize the glasses. Si was coordinated in Q 2 and Q 3 units, Al was four-coordinated, and B was mostly three-coordinated. The rhenium additions did not have significant effects on the glass structure up to approximately 3000 ppm Re by mass, the maximum concentration that remained dissolved in glass. Rhenium likely exists in isolated ReO À 4 anions in the interstices of the glass network, as evidenced by polarized Raman spectrum of the Re glass in the absence of sulfate. Analogous to SO 2À 4 in similar glasses, ReO À 4 is a network modifier and above solubility forms alkali salt phases on the surface and in the bulk. Comparisons of phase separation and crystallization in MoO 2À 4 containing borosilicate glasses can also be made to ReO À 4 containing glasses.

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Section: Technetium and Rheniummentioning

confidence: 99%

Section: Technetium and Rheniummentioning

confidence: 99%

Structure of Rhenium‐Containing Sodium Borosilicate Glass

Goel

McCloy

Windisch

et al. 2012

Int J of Appl Glass Sci

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“…Rhenium (Re) has been the preferred nonradioactive 99 Tc surrogate because of the similarities of Re to 99 Tc in chemistry, ionic size, speciation in glass, and volatility in glass [20]. It is known that Re and 99 Tc behave differently when redox reactions are involved because of the differences in reduction potentials of Re 7+ and Tc 7+ [21][22][23][24], yet the chemistry of the two elements is similar when in the same oxidation state. Kim et al [21] investigated the behavior of 99 Tc and Re during crucible melting of simulated Hanford LAW glass feeds designed for bulk vitrification technology demonstration.…”

Section: Introductionmentioning

confidence: 99%

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Jin

Kim

Tucker

et al. 2015

Journal of Non-Crystalline Solids

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a b s t r a c tVolatile loss of radioactive technetium-99 ( 99 Tc) to off-gas is a major challenge when vitrifying low-activity waste (LAW) at the U.S. Department of Energy's Hanford Site in Washington State. We investigated the partitioning and incorporation of rhenium (Re) (a nonradioactive surrogate for 99 Tc) into the glass melt during crucible melting of two simulated LAW feeds that have exhibited a large difference in 99m Tc/Re retention in glass from small-scale melter tests. Each feed was prepared from a simulated liquid LAW and additives (boric acid, silica sand, etc.). The as-mixed slurry feeds were dried at 105°C and heated to 600-1100°C at 5 K/min. The dried feeds and heat-treated samples were leached with deionized water for 10 min at room temperature followed by 24-h leaching at 80°C. Chemical compositions of the resulting solutions and insoluble solids were analyzed. Volume expansion measurements and X-ray diffraction (XRD) analyses were performed on dried feeds and heat-treated samples to characterize the progress of feed-to-glass conversion reactions. We found that incorporation of Re into the glass melt was virtually completed during the major feed-to-glass conversion reactions that occurred at ≤700°C. The results of our study suggest that the different compositions of the salt phases formed during early stages of melting at ≤700°C are responsible for the large difference in Re incorporation into the glass melt in these two feeds.

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“…However, only a few studies were dedicated to glass vapor hydration. [25][26][27][28][29][30][31] Recent papers on the vapor hydration of borosilicate glasses have been published by McKeown et al 32,33 and Buechele et al 34 The authors used state-of-art spectroscopic techniques to investigate the glass alteration layer. Hence, Raman and X-ray absorption spectroscopic studies showed that, at high temperature (200 C) and short time periods (3-20 days), the major hydration product is a depolymerized hydrated altered glass with some crystals of analcime and leucite.…”

Section: Introductionmentioning

confidence: 99%