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Studies to Improve 99 Tc Management Strategy for Hanford Waste Vitrification Dongsang Kim, John S. McCloy, Brian J. Riley, Mike J. Schweiger, Pavel R.

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Presentation on theme: "Studies to Improve 99 Tc Management Strategy for Hanford Waste Vitrification Dongsang Kim, John S. McCloy, Brian J. Riley, Mike J. Schweiger, Pavel R."— Presentation transcript:

1 Studies to Improve 99 Tc Management Strategy for Hanford Waste Vitrification Dongsang Kim, John S. McCloy, Brian J. Riley, Mike J. Schweiger, Pavel R. Hrma, Jarrod V. Crum, Chuck Z. Soderquist, Steven A. Luksic, Carolyn I. Pearce, Tongan Jin, Wayne Lukens (1) File Name // File Date // PNNL-SA-##### Introduction Hanford tank wastes are planned to be separated into high-level waste (HLW) and low-activity waste (LAW) and vitrified separately. Hanford site contains ~1500 kg (~25,000 Ci) of 99 Tc and >90% of the 99 Tc inventory is to be immobilized in LAW glass. The major environmental concern with 99 Tc is its high mobility in addition to a long half life (213,000 y). The highly soluble TcO 4- does not adsorb well onto the surface of minerals, and thus, migrates at the same velocity as groundwater. Primary concern with processing the Hanford LAW into glass is its high volatility and hence low retention in glass. The objective is to improve technetium management strategy for Hanford LAW vitrification through: developing technologies to incorporate technetium into high-temperature minerals that can be used to increase its retention in glass fundamental understanding of the partitioning of technetium during conversion of LAW feed into glass Understand the partitioning of 99 Tc into various phases (salts, early glass forming melts, intermediate reaction phases, etc.) and volatilization of 99 Tc from these phases during cold cap melting Eventually to develop the approaches to maximize the Tc retention in glass Solubility of 99 Tc in LAW Glass This work was supported by the Department of Energy’s Waste Treatment & Immobilization Plant Federal Project Office under the direction of Dr. Albert A. Kruger. Develop experimental techniques for solubility using Re as a surrogate and measure Re solubility Measure 99 Tc solubility for reduced (Tc 4+ ) and oxidized (Tc 7+ ) species Mechanism of 99 Tc Volatilization from LAW Melt Mineral that dissolves and releases Tc into glass at high temperatures minimizing Tc loss during cold cap melting Mineral that may be used as a stand alone waste form  Fused quartz ampoule  Vacuum sealed  Batch: baseline glass + Tc/Re-source  Target Re: ,000 ppm mass  Target 99 Tc: ,000 ppm mass  Batch size: g  Heat treating at 1000°C for 2 h  Quenching in air Vacuum sealing Out of furnace after 2 h at 1000°C Final glass Example Pictures from 99 Tc Test SEM micrographs, phase map, and elemental distribution for crystals found on the surface of the Re test glass Baseline glass + KTcO 4 Baseline Glass Composition Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) signal versus time, showing (a) the presence of Re inclusions and (b) depth profiling glass salt Incorporation of 99 Tc from Off-gas Stream into Minerals Methods that are being explored to synthesize Re/Tc incorporating minerals  Aqueous and heat treatment (“wet chemical” method) of trevorite Trevorite (NiFe 3+ 2 O 4 ) is stable to oxidation compared to Fe 2+ in magnetite (Fe 2+ Fe 3+ 2 O 4 )  Molten salt method Chlorides salt as a reaction medium, under ambient atmosphere or in a sealed ampoule Trevorite, franklinite (ZnFe 2 O 4 ), and geikielite (MgTiO 3 ) were synthesized KReO 4, ReO 2, and K 2 ReCl 6 were used as a Re source (surrogate for Tc)  High-temperature reaction of oxides Trevorite, franklinite, geikielite, rutile (TiO 2 ), and quandilite (NiZnTiO 4 ) were synthesized RuO 2 was used as a Ru source (surrogate for Tc)  Aqueous method Solution derived synthesis of magnetite doped with Re or Tc Future Plans Molten Salt synthesis of trevorite with Tc (Tc is expected to form spinel more readily than Re) Re/Tc incorporation into solution derived Fe 3-x Re x O 4 and Fe 3-x Tc x O 4 Improve calcining procedure to retain Re in the spinel and produce larger particles Synthesize Re- and Tc-sodalite from Na 2 ReCl 6 /K 2 ReCl 6 and Na 2 TcCl 6 /K 2 TcCl 6 Incorporate resulting spinel phases into a typical glass feed and measure Re retention in comparison with KReO 4 or K 2 ReCl 6 Perform laboratory-scale melter (slurry fed, with Re and or 99Tc) tests to verify Re/Tc retention enhancement Future Plans Evaluate Re partitioning results in relation to mass loss, feed volume expansion, XRD phase identification Design next set of crucible tests including: Effect of heating conditions (heating rate or simulated melter schedule, etc.) Effect of reducing agents (varied carbon sources chemical and amount) Modified feeds (AN-102 and/or AZ-102 feed modified for selected feed components) If successful approaches are developed, perform laboratory-scale melter tests (slurry fed, with Re and or 99Tc) for selected feed and test variables and recommend scaled melter tests 600°C 700°C 800°C 900°C 1000°C 1100°C AN-102 (medium sulfate, high nitrates) AZ-102 (high sulfate, low nitrates) Surface salt observed at ≥ 800°C (salt formation is specific to the crucible test conditions of dried feeds, i.e., these feeds were processed in scaled meter tests without salt formation) Preliminary Conclusions Considering that the projected concentration of 99 Tc in Hanford LAW glass is <10 ppm, solubility of Tc in glass is not likely to limit its retention Although the high Tc concentration used in solubility test is not directly relevant to LAW processing, information learned on the structural role and partitioning of Re in relation to S and on the behavior of two 99 Tc species is helpful for current studies on “incorporation of 99 Tc from off-gas stream into minerals” and “mechanism of 99 Tc In escape from LAW feed/melt XANES: ~100% Re(VII) Test Conditions Fused silica (1) Lawrence Berkeley National Laboratory Glass with 6400 ppm (target) Re WC milled SEM-EDS of the surface of glass containing 6000 ppm (target) 99 Tc Tc K edge X-ray absorption near-edge structure (XANES) spectrum of glass containing 3000 ppm (target) 99 Tc WC milled Measured (a) Re and (b) 99 Tc concentrations in bulk glass Raman spectroscopy, X-ray photoelectron spectroscopy, and magic angle spinning-nuclear magnetic resonance are underway for Tc solubility samples to further investigate Tc speciation (a) (b) XANES: ≥ 90% Tc(IV) with TcO 2 in 1000 and 3000 ppm samples in WC milled % Tc(IV) in corundum milled Example XANES spectra of trevorite sample with 10% Re 2 O 7 (target) O Al Fe Ni Re Trevorite (NiFe 3+ 2 O 4, confirmed by XRD) synthesized by wet chemical method Fraction (29 to 53%) of Re is in reduced form, probably Re(VI) → Re is not likely structurally bound to trevorite: Re(IV) is expected if Re was structurally bound Trevorite (NiFe 3+ 2 O 4 ) synthesized by molten salt method Rhenium added as ReO 2 does not join the spinel structure Re-doped magnetite particles formed by solution derived synthesis before (left) and after (right) coarsening for 12 h at 300°C under N 2 Crucible melting of high-level waste glass added with spinel Experimental Method of Initial Re Partitioning Tests  Prepare and dry simulated slurry feeds with Re 2 O 7 to have 8.1 ppm Re in glass (AN-102 and AZ-102)  Measure feed volume change as a function of temperature using pellets prepared from dried feeds  Heat dried feeds at 5 °C/min to 600 – 1100°C at 100 °C interval and air cool  Perform 3-step wash/leach for each heat treated sample First room temperature rinse for 10 min in 200 ml DI water Soak for 24 h at 80°C in a sealed container, filter solution out, and dry the remaining solids Second room temperature rinse for 10 min in 200 ml DI water Top view of heat treated samples  Sodium nitrate is the only waste simulant component detected  Boric acid and lithium carbonate that were added in relatively large quantity were not identified => likely mixed into amorphous phases during slurry preparation and drying Fraction of Re analyzed in solution (total from 3 samples) and solid samples AN °C samples are being reanalyzed Preliminary notes: AN-102 contained higher fraction of Re in the soluble phases (see “Dissolved” for ≤ 800°C) than AZ-102 and resulted in lower Re retention in the final glass (see “Retained in solid” for 1100°C) Detailed analyses of all feed components in relation to other test results are in progress XRD of heat treated samples


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