Hollandite-rich Ceramic Melts for the Immobilisation of Cs

Carter, M. L.; Vance, E. R.; Li, H.

doi:10.1557/proc-807-249

Cited by 19 publications

(16 citation statements)

References 3 publications

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“…The successful demonstration of melt processing of ceramic waste forms achieving the targeted phases has been accomplished, however there were additional crystalline phases observed that possessed low durability, specifically the alkali molybdate phases. This is being addressed by varying the transition metal elements in the hollandite structure [9] to facilitate Cs incorporation into the hollandite structure to minimize secondary Cs-Mo phase formation and continued processing in reducing conditions using metal/metal oxide buffers such as Ti/TiO 2 [10].…”

Section: Reference Composition-target Vs Achieved Phase Formationmentioning

confidence: 99%

“…Hollandite derived ceramic waste forms for immobilization of Cs have been previously melted in air using Cr, Ni, Zn or Co transition metal substitutions resulting in PCT-B normalized leachate concentrations below 0.2 g/L [9]. The present study used melt processing in air to fabricate three single phase hollandite ceramics with the following stoichiometries: The Fe-Hollandite sample was used as a baseline composition from which to compare phase formation and Cs incorporation.…”

Section: Single Phase Hollandite-composition and Processingmentioning

confidence: 99%

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Crystalline Ceramic Waste Forms: Report Detailing Data Collection In Support Of Potential FY13 Pilot Scale Melter Test

Brinkman¹,

Amoroso²,

Marra³

et al. 2012

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v SUMMARYThe research conducted in this work package is aimed at taking advantage of the long term thermodynamic stability of crystalline ceramics to create more durable waste forms (as compared to high level waste glass) in order to reduce the reliance on engineered and natural barrier systems. Durable ceramic waste forms that incorporate a wide range of radionuclides have the potential to broaden the available disposal options and to lower the storage and disposal costs associated with advanced fuel cycles. Assemblages of several titanate phases have been successfully demonstrated to incorporate radioactive waste elements, and the multiphase nature of these materials allows them to accommodate variation in the waste composition. Recent work has shown that they can be successfully produced from a melting and crystallization process. The objective of this report is to summarize the data collection in support of future melter demonstration testing for crystalline ceramic waste forms.The waste stream used as the basis for the development and testing is a combination of the projected Cs/Sr separated stream, the Trivalent Actinide -Lanthanide Separation by Phosphorous reagent Extraction from Aqueous Komplexes (TALSPEAK) waste stream consisting of lanthanide fission products, the transition metal fission product waste stream resulting from the transuranic extraction (TRUEX) process, and a high molybdenum concentration with relatively low noble metal concentrations.The principal difficulties encountered during processing of the "reference ceramic" waste form by a melt and crystallization process were the incomplete incorporation of Cs into the hollandite phase and the presence of secondary Cs-Mo non-durable phases. In the single phase hollandite system, these issues were addressed in this study by refining the compositions to include Cr as a transition metal element and the use of Ti/TiO 2 buffer to maintain reducing conditions. Initial viscosity studies of ceramic waste forms indicated that the pour spout must be maintained above 1400 o C to avoid flow blockages due to crystallization. In-situ electron irradiations simulate radiolysis effects indicated hollandite undergoes a crystalline to amorphous transition after a radiation dose of 10 13 Gy which corresponds to approximately 1000 years at anticipated doses (2×10 10 -2×10 11 Gy). Dual-beam ion irradiations employing light ion beam (such as 5 MeV alpha) and heavy ion beam (such as 100 keV Kr) studies indicate that reference ceramic waste forms are radiation tolerant to the β-particles and α-particles, but are susceptible to a crystalline to amorphous transition under recoil nuclei effects.A path forward for refining the processing steps needed to form the targeted phase assemblages is outlined in this report. Processing modifications including melting in a reducing atmosphere with the use of Ti/TiO 2 buffers, and the addition of Cr to the transition metal additives to facilitate Cs-incorporation in the hollandite phase. In addition to melt processing, alternative f...

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Section: Reference Composition-target Vs Achieved Phase Formationmentioning

confidence: 99%

Section: Single Phase Hollandite-composition and Processingmentioning

confidence: 99%

Crystalline Ceramic Waste Forms: Report Detailing Data Collection In Support Of Potential FY13 Pilot Scale Melter Test

Brinkman¹,

Amoroso²,

Marra³

et al. 2012

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show abstract

“…Existing literature has focused Cs-rich waste targeted in dual phase hollandite/rutile mixtures fabricated via melt processing in air. [13] Hollandite formation based on dopants of Zn, Co, or Ni were successfully demonstrated in binary systems by melt processing in air. However, it is believed that reducing environments will be required to avoid molybdate (Cs-Mo) phase formation in the multiphase FCR&D waste forms of interest.…”

Section: Single Phase Hollanditementioning

confidence: 99%

“…[14][15][16][17] In general, many of those trivalent and divalent cations were effective in promoting Cs incorporation into the hollandite, but also promoted secondary phase formation. Dopants which have the atomic radius appropriate for the M +3 site in the hollandite are not found in the anticipated waste streams.…”

Section: Composition and Processing Conditionsmentioning

confidence: 99%

Crystalline Ceramic Waste Forms: Comparison Of Reference Process For Ceramic Waste Form Fabrication

Brinkman

Marra

Amoroso

et al. 2013

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v SUMMARYThe research conducted in this work package is aimed at taking advantage of the long term thermodynamic stability of crystalline ceramics to create more durable waste forms (as compared to high level waste glass) in order to reduce the reliance on engineered and natural barrier systems. Durable ceramic waste forms that incorporate a wide range of radionuclides have the potential to broaden the available disposal options and to lower the storage and disposal costs associated with advanced fuel cycles. Assemblages of several titanate phases have been successfully demonstrated to incorporate radioactive waste elements, and the multiphase nature of these materials allows them to accommodate variation in the waste composition. Recent work has shown that they can be produced from a melting and crystallization process. The objective of this report is to explore the phase formation and microstructural differences between lab scale melt processing in varying gas environments with alternative densification processes such as Hot Pressing (HP) and Spark Plasma Sintering (SPS).The waste stream used as the basis for the development and testing is a simulant derived from a combination of the projected Cs/Sr separated stream, the Trivalent Actinide -Lanthanide Separation by Phosphorous reagent Extraction from Aqueous Komplexes (TALSPEAK) waste stream consisting of lanthanide fission products, the transition metal fission product waste stream resulting from the transuranic extraction (TRUEX) process, and a high molybdenum concentration with relatively low noble metal concentrations.Melt processing as well as solid state sintering routes SPS and HP demonstrated the formation of the targeted phases; however differences in microstructure and elemental partitioning were observed. In SPS and HP samples, hollandite, pervoskite/pyrochlore, zirconolite, metallic alloy and TiO 2 and Al 2 O 3 were observed distributed in a network of fine grains with small residual pores. The titanate phases that incorporate M +3 rare earth elements were observed to be distinct phases (ex. Nd 2 Ti 2 O 7 ) with less degree of substitution as compared to the more homogeneous melt processed samples where a high degree of substitution and variation of composition within grains was observed. Liquid phase sintering was enhanced in reducing gas environments and resulted in large (10-200 microns) irregular shaped grains along with large voids associated with the melt process; SPS and HP samples exhibited finer grain size with smaller voids. Metallic alloys were observed in the bulk of the sample for SPS and HP samples, but were found at the bottom of the crucible in melt processed trials. These results indicate that for a first melter trial, the targeted phases can be formed in air by utilizing Ti/TiO 2 additives which aid phase formation and improve the electrical conductivity. Ultimately, a melter run in reducing gas environments would be beneficial to study differences in phase formation and elemental partitioning.

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“…The dissolution rates of all species decreased with increasing 11 leach time due to the formation of partly impervious surface coatings of Al and Ti rich species. [17] In 2004, ANSTO reported on studies conducted with hollandite-rich ceramic melts for immobilization of Cs. The titanate Synroc phase hollandite (Ba x Cs y M 3+ 2x-y Ti 8-2x-y O 16 where trivalent M = Al in oxidizing conditions and Al and Ti in reducing conditions) is well known for its ability to incorporate Cs when produced by hot pressing with excellent leach resistance.…”

Section: Australia 2002mentioning

confidence: 99%

Evaluation of the Use of Synroc to Solidify the Cesium and Strontium Separations Product from Advanced Aqueous Reprocessing of Spent Nuclear Fuel

Tripp¹,

Garn²,

Boardman³

et al. 2006

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Hollandite-rich Ceramic Melts for the Immobilisation of Cs

Cited by 19 publications

References 3 publications

Crystalline Ceramic Waste Forms: Report Detailing Data Collection In Support Of Potential FY13 Pilot Scale Melter Test

Crystalline Ceramic Waste Forms: Report Detailing Data Collection In Support Of Potential FY13 Pilot Scale Melter Test

Crystalline Ceramic Waste Forms: Comparison Of Reference Process For Ceramic Waste Form Fabrication

Evaluation of the Use of Synroc to Solidify the Cesium and Strontium Separations Product from Advanced Aqueous Reprocessing of Spent Nuclear Fuel

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