Rhenium Solubility in Borosilicate Nuclear Waste Glass: Implications for the Processing and Immobilization of Technetium-99

McCloy, John S.; Riley, Brian J.; Goel, Ashutosh; Liezers, Martin; Schweiger, Michael J.; Rodriguez, Carmen P.; Hrma, Pavel R.; Kim, Dong-Sang; Lukens, Wayne W.; Kruger, Albert A.

doi:10.1021/es302734y

Cited by 65 publications

(149 citation statements)

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“…The loading of technetium in LAW glass can be increased by using reducing conditions (Fe(II)/Fe tot ~0.25), up to ~3000 ppm total technetium. Contrary to our previous hypotheses, 20 the solubility of Tc(VII) (estimated to be ~900 ppm in these glass samples) is lower than predicted by arguments based on ionic radii, and the solubility of Tc(IV) (estimated to be ~2600 ppm in these glasses) appears to be quite high.…”

Section: Environmental Impactcontrasting

confidence: 99%

“…Given that the estimated concentration of technetium in LAW glass at Hanford is ~3 ppm, 20 the technetium solubility in glass should not be a factor in technetium retention regardless of its oxidation state. Likewise, at the Defense Waste Processing Facility in Aiken, South Carolina, the highest estimated Tc concentrations in actual glasses measured were ~33 ppm which most being <8 ppm, and >80% of the Tc was found to be retained (based on measured radioactivity) at a melt redox of Fe(II)/Fe tot ~0.2.…”

Section: Environmental Impactmentioning

confidence: 99%

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Redox-dependent solubility of technetium in low activity waste glass

Soderquist

Schweiger

Kim

et al. 2014

Journal of Nuclear Materials

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The solubility of technetium was measured in a Hanford low activity waste glass simulant. The simulant glass was melted, quenched and pulverized to make a stock of powdered glass. A series of glass samples were prepared using the powdered glass and varying amounts of solid potassium pertechnetate. Samples were melted at 1000°C in sealed fused quartz ampoules. After cooling, the bulk glass and the salt phase above the glass (when present) were sampled for physical and chemical characterization. Technetium was found in the bulk glass up to 2000 ppm (using the glass as prepared) and 3000 ppm (using slightly reducing conditions). The chemical form of technetium obtained by x-ray absorption near edge spectroscopy can be mainly assigned to isolated Tc(IV), with a minority of Tc(VII) in some glasses and TcO 2 in two glasses. The concentration and speciation of technetium depends on glass redox and amount of technetium added. Solid crystals of pertechnetate salts were found in the salt cake layer that formed at the top of some glasses during the melt. BackgroundRadioactive waste from decades of plutonium production is currently stored in large underground tanks at the Hanford Site. This waste will be mixed with glass formers and then vitrified. 1 The Hanford tank wastes vary widely in composition, but are typically largely sodium nitrate, nitrite, and carbonate with a small amount of hydroxide.2; 3 Aluminum, iron and zirconium comprise 20% or more of the waste in some cases. Chromium and manganese may be present up to several percent. not recover all of the plutonium from the irradiated uranium, and a small amount of plutonium, uranium and americium are also found in the tanks. Many of the waste components do not incorporate well into silicate glasses. A number of ionic compounds such as sulfates have low solubility in silicate glasses and may form a separate salt phase.The current plan is to chemically separate the waste into a small volume of high-level waste, intensely radioactive from 90 Sr and 137 Cs, and a large volume of low-activity waste (LAW). 1 These two fractions will be vitrified separately. Technetium will report to the low-activity waste and will be vitrified in that fraction. Tc in LAW GlassPage 2 of 21Technetium incorporates poorly into silicate glass in traditional glass melting. Technetium readily evaporates during melting of glass feeds (waste + additives) and out of the molten glass, leading to low retention in a final glass product. [4][5][6][7] To effectively manage technetium retention in the Hanford LAW glass, it is critical to understand if the solubility of technetium is a controlling factor. The speciation of technetium in glass has been previously studied, and the technetium species present in waste glass have been previously reported; [8][9][10][11] however, the solubilities of these species are unknown.The solubility of technetium and many other waste constituents depends partly on their chemical forms.A particular constituent may be better incorporated into the glass if it is adde...

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Section: Environmental Impactcontrasting

confidence: 99%

Section: Environmental Impactmentioning

confidence: 99%

Redox-dependent solubility of technetium in low activity waste glass

Soderquist

Schweiger

Kim

et al. 2014

Journal of Nuclear Materials

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“…Included in the inventory of highly radioactive wastes is large volumes of 99 Tc (∼9 × 10 2 TBq or ∼2.5 × 10 4 Ci or ∼1500 kg). [2] This paper describes the coordinated environment of perrhenates and pertechnetates (1) in glasses when KReO 4 or KTcO 4 were added to the simulated LAW [3,4] glass and (2) in crystalline compounds. The KReO 4 or KTcO 4 was added to the glass in order to study the impact of 99 Tc on the properties and performance of highly radioactive glass formulations for long-term storage.…”

Section: Introductionmentioning

confidence: 99%

“…Raman microscopy was used here to probe local environments in the glass structure and to study the crystallization behavior previously observed on the surface of the LAW glass. [3,4] The pertechnetate ion (TcO 4 À ) is the dominant form of Tc metal in the oxidizing environment of the waste tanks. Preliminarily, perrhenate (ReO 4 À ) was used as a nonradioactive surrogate for pertechnetate to probe the effects of the ion on the coordinated silicate, borate, and aluminate networks.…”

Section: Introductionmentioning

confidence: 99%

“…[5,6] The incorporation of ReO 4 À in alumino-borosilicate glasses was previously measured by conventional Raman spectroscopy, X-ray absorption near edge structure spectroscopy, nuclear magnetic resonance spectrometry, and X-ray diffraction (XRD) analysis. [4,7] A subset of these measurements were performed on analogous Tc-containing glasses, and results are presented elsewhere. [8] This work presents data from high spatial-resolution and high spectral-resolution Raman microscopy, which probed the local structure within the glasses as well as crystalline phases on the bulk glasses.…”

Section: Introductionmentioning

confidence: 99%

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Raman analysis of perrhenate and pertechnetate in alkali salts and borosilicate glasses

Gassman

McCloy

Soderquist

et al. 2014

J Raman Spectroscopy

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Sodium borosilicate glasses containing rhenium or technetium were fabricated and their vibrational spectra studied using confocal Raman microscopy. Glass spectra were interpreted relative to new high-resolution spectra of pure crystalline NaReO 4 , KReO 4 , NaTcO 4 , and KTcO 4 salts. Spectra of perrhenate and pertechnetate glasses exhibited sharp Raman bands, characteristic of crystalline salt species, superimposed on spectral features of the borosilicate matrix. At low concentrations of added KReO 4 or KTcO 4, the characteristic pertechnetate and perrhenate features are weak, whereas at high additions, sharp peaks from crystal field-splitting and C 4h symmetry dominate glass spectra, clearly indicating ReO 4 À or TcO 4 À is locally coordinated with K and/or Na. Peaks indicative of both K and Na salts are evident in many Raman spectra, with the Na form being favored at high concentrations of the source chemicals, where more K + is available for ion exchange with Na + from the base glass. The observed ion exchange likely occurred within depolymerized channels where nonbridging oxygens create segregation from the glass network in regions containing anions such as ReO 4 À and TcO 4 À as well as excess alkali cations. Although this anion exchange provides evidence of chemical mixing in the glass, it does not prove the added salts were homogeneously incorporated in the glass. The susceptibility to ion exchange from the base glass indicates that long-term immobilization of Tc in borosilicate glass must account for excess charge compensating alkali cations in melt glass formulations. Published 2014. This article is a U. S. Government work and is in the public domain in the USA.Additional supporting information may be found in the online version of this article at the publisher's web site.

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