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The radioisotope 129 I, a fission product in spent nuclear fuel, has a long half-life, and can be highly mobile in the environment. Iodine K-edge X-ray absorption spectra were collected to characterize the iodine valence and coordination environment in simulated Hanford low activity waste glasses. Both iodine XANES and EXAFS data for eleven borosilicate glasses indicate iodide-like environments within the glass structure, where I � has Na or Li nearest-neighbors, and where the nearest-neighbor cation-type correlates to the most common network-modifying cation in the glass. This is further supported by the systematic increase of iodine incorporation with the combined Na2 O+L i 2O content in the glass. EXAFS analyses determined I–Na distances near 3.04 A with coordination numbers near 4.0 and I–Li distances near 2.80 A with coordination numbers near 3.0. I–Na environments determined for the glasses are similar to the tetrahedral INa4 coordination found in NaI-sodalite. These weakly bound iodine-alkali configurations may be the only pathways for iodine to be retained in the glass. These environments may be precursors to NaI-sodalite crystallization in Na-rich glass. Iodine also shows distinct differences from chlorine in terms of the preferred sites in the glass structure.

The concentration of sulfur in Hanford low-activity waste (LAW) glass melter feed will be maintained below the point where the salt accumulates on the melt surface. The allowable concentrations may range from near zero to over 2.05 wt% (of SO3 on a calcined oxide basis) depending on the composition of the melter feed and processing conditions. If the amount of sulfur exceeds the melt tolerance level, a molten salt will accumulate which may upset melter operations and potentially shorten the useful life of the melter. At the Hanford site, relatively conservative limits have traditionally been placed on sulfur loading in melter feed, which in turn significantly increases the amount of LAW glass that will be produced. Crucible-scale sulfur solubility data and scaled melter sulfur tolerance data have been collected on simulated Hanford waste glasses over the last 15 years. These data were compiled and analyzed. An empirical model was developed to predict the solubility of SO3 in glass based on 253 simulated Hanford LAW glass compositions. This model represents the data well, accounting for over 85% of the variation in data, and was well validated. The model was also found to accurately predict the maximum amount of sulfur in melter feed that did not form a salt layer in 13 scaled melter tests of simulated LAW glasses. The model can be used to help estimate glass volumes and make informed decisions on process options (e.g., scale of supplemental LAW treatment facility, and pretreatment facility performance requirements). The model also gives quantitative estimates of component concentration effects on sulfur solubility. The components that increase sulfur solubility most are Li2O > V2O5 > CaO ≈ P2O5 > Na2O ≈ B2O3 > K2O. The components that decrease sulfur solubility most are Cl > Cr2O3 > Al2O3 > ZrO2 ≈ SnO2 > Others (i.e., the sum of minor components) ≈SiO2. The order of component effects is similar to previous literature data, in most cases.

X-ray absorption spectroscopy (XAS) was used to characterize vanadium (V) and chromium (Cr) environments in low activity nuclear waste (LAW) glasses synthesized under a variety of redox conditions. V2O5 was added to the melt to improve sulfur incorporation from the waste; however, at sufficiently high concentrations, V increased melt foaming, which lowered melt processing rates. Foaming may be reduced by varying the redox conditions of the melt, while small amounts of Cr are added to reduce melter refractory corrosion. Three parent glasses were studied, where CO–CO2 mixtures were bubbled through the corresponding melt for increasing time intervals so that a series of redox-adjusted-glasses was synthesized from each parent glass. XAS data indicated that V and Cr behaviors are significantly different in these glasses with respect to the cumulative gas bubbling times: V4+/Vtotal ranges from 8 to 35%, while Cr3+/Crtotal can range from 15 to 100% and even to population distributions including Cr2+. As Na-content decreased, V, and especially, Cr became more reduced, when comparing equivalent glasses within a series. The Na-poor glass series show possible redox coupling between V and Cr, where V4+ populations increase after initial bubbling, but as bubbling time increases, V4+ populations drop to near the level of the parent glass, while Cr becomes more reduced to the point of having increasing Cr2+ populations.

Technetium-99 is a long half-life radioactive fission product whose high volatility during waste vitrification (National Research Council, 2001; Migge, Mat Res Symp Proc 127:205–213, 1989) is a factor in the safe disposal of radioactive waste. Oxidation states of +7, +4 mostly, and some traces of metal have been observed in the glass (Migge, Mat Res Symp Proc 176:411–417, 1990; Darab and Smith, Chem Mater 8:1004–1021, 1996) with Tc7 + more volatile than Tc4 + , leading to a range of technetium retention in the glass varying from 0.8% to 92%. In the present experiments, a simulated high-sulfate Hanford tank waste was vitrified using a slurry fed joule heated furnace producing about 30 kg of glass per day. Various combinations of sucrose and urea were used as denitration and reducing agents in order to optimize sulfate and technetium retention. Since iron oxide is used as a glass additive, Fe-Mossbauer spectroscopy was a vital tool to monitor the melt redox through its Fe2 + /Fetot ratio. A Mossbauer glass redox scale was designed to relate the technetium speciation to its retention in the glass.

This report describes the results of testing specified by the Enhanced LAW Glass Property-Composition Models, VSL-13T3050-1, Rev. 0 Test Plan. The work was performed in compliance with the quality assurance requirements specified in the Test Plan. Results required by the Test Plan are reported. The te4st results and this report have been reviewed for correctness, technical adequacy, completeness, and accuracy.

This report presents the results of glass formulation development with TWRS LAW simulants that was conducted at the Vitreous State Laboratory of The Catholic University of America during TWRS Phase I.

The main objective of the work was to develop and select a glass formulation for vitrification testing of the actual waste sample of LAW AP-101 at Battelle - Pacific Northwest Division (PNWD). Other objectives of the work included preparation and characterization of glasses to demonstrate compliance with contract and processing requirements, evaluation of the ability to achieve waste loading requirements, testing to demonstrate compatibility of the glass melts with melter materials of construction, comparison of the properties of simulant and actual waste glasses, and identification of glass formulation issues with respect to contract specifications and processing requirements.

The main objective of the work is to develop a correlation that employs waste composition information to determine the appropriate waste loading, glass composition, and amounts and types of glass formers. In addressing this objective emphasis has been placed on those compositions that have been validated in DM100 and LAW Pilot Melter testing. This is particularly important in view of the essential role that potential for sulfate phase separation in the melter plays in glass formulation selection. A further objective of this work is to select and test glass compositions in order to augment the existing data set and to test the predictions from the correlation. It should be noted that the intent of the correlation is to provide practical, robust glass formulations that exceed all of the contract and processability requirements; it is not intended to provide the "maximum achievable" waste loading such that at least one of those properties is at its respective limit.

Sulfur can be the waste-loading limiting constituent for vitrification of sulfur-bearing radioactive wastes due to low solubility in silicate melts. Methods to improve sulfur loading would benefit from improved understanding of the structural aspects of sulfur incorporation in borosilicate and other glasses. To this end, sulfur XANES spectra were collected for eight crystalline standards and twenty-four glasses, including borosilicate, phosphate, and borate compositions. Spectra for the standards show a systematic energy shift of the sulfur K-edge from 2469 to 2482 eV, as sulfur valence increases from 2− (in sulfides) to 6+ (in sulfates). Most crucible glasses investigated have simple edges near 2482 eV that indicate sulfur in the form of sulfate only. Other glasses, some synthesized under reducing conditions, have complicated edges, indicating sulfate, sulfite, and more reduced species that may include S, S–S doublets, or short polysulfide chains. Sulfide species (S2−) were not dominant in any of the samples over the range of redox conditions investigated. These results indicate that sulfur incorporation is considerably more complex than would be suggested by the conventional interpretation of the redox-dependence of sulfur solubility, which considers only sulfate and sulfide species. Raman data indicate that several of the glasses investigated are not homogeneous with regard to all sulfur species.

X-ray absorption spectroscopic data were collected and analyzed to characterize vanadium in borosilicate glasses used for immobilization of sulfur-containing nuclear wastes. Data are presented for borosilicate glasses, some with and some without sulfur, that have V2O5 concentrations as high as 12 wt%, and for the sulfides: sulvanite and patronite, the silicates: cavansite, hadaraite, and roscoelite, and the oxide: vanadinite. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data for the glasses have no sulfur dependent features, but do show changes that parallel various redox conditions for the corresponding melts. EXAFS data for the glasses indicate V–O distances near 1.70 A that are considerably shorter than typical V–S distances found in the sulfides. Both XANES and EXAFS indicate that most or all vanadium in these glasses is in the form of V5+O4 tetrahedra; glasses synthesized under reducing conditions can have penta-coordinated V4+ populations up to approximately 20–25% of all vanadium present.

Raman spectroscopy has been used to characterize sulfur environments in a variety of borosilicate glass formulations developed for long-term radioactive waste storage. The spectra of these glasses all have S–O symmetrical stretch modes (ν1) near 1000 cm −1 from tetrahedral SO4 (sulfate) environments. The Raman data indicate that the sulfate environments are independent of the borosilicate network; in particular, isolated SO4 tetrahedra in the glass are surrounded by network modifying cations, such as Na. By changing the type of network modifying cations in the borosilicate glass, the ν1 peak shifts, in such a way that larger cation charge densities correlate to higher ν1 frequencies. The ν1 peak for Li, Ca, Na, K, and Cs borosilicate glasses is broadened and shifted to lower frequencies with respect to ν1 for Li, Ca, Na, K, and Cs sulfate crystals, respectively; this indicates that sulfate tetrahedra in borosilicate glass are more disordered and more weakly bonded to their surrounding environments than sulfate tetrahedra in the corresponding sulfate crystals.

Polarized Raman spectra were obtained for a collection of borosilicate glasses that have been developed as candidate compositions for the immobilization of wastes generated from the reprocessing of Zircaloy-clad spent nuclear fuel. Raman spectra were obtained for borosilicate glasses with zirconia compositions as high as 21 wt%, as well as for crystalline ZrO2 (baddeleyite) and crystalline ZrSiO4 (zircon). As zirconia content in the glass is increased, two trends in the spectra indicate that the partially polymerized silicate tetrahedral network becomes more depolymerized: one, the polarized mid frequency envelope near 450 cm ˇ1 , assigned to Si‐O‐Si symmetrical bend modes, decreases in area; and two, the higher frequency band assigned to Si‐O stretch in Q 2 units (silicate chains) increases in area, while band areas decrease for modes assigned to Si‐O stretch in more polymerized Q 3 and Q 4 units (silicate sheets and cages). These trends take place whether the glass composition is relatively simple or considerably more complex. As zirconia concentrations in the glass increase beyond 15 wt%, a series of sharp lines are observed in the spectra from baddeleyite crystals, and to a minor extent Zn‐Cr spinel phases, superimposed on broad features from the glass matrix. A low intensity, broad band near 1400 cm ˇ1 in the glass spectra is probably due to B‐O stretch modes within BO3 units. ” 2000 Elsevier Science B.V. All rights reserved.

The Zn environments in six zirconium borosilicate glasses were characterized using X-ray absorption spectroscopy (XAS). The Zn environment is of interest because the addition of ZnO to borosilicate glass produces beneficial eAects on certain bulk physical properties that are important in the production and long-term storage of radioactive waste glasses. Zn XAS data and analyses show that all glass samples investigated contain Zn aa surrounded by four oxygens in tetrahedral coordination, with most likely, Si second nearest neighbors. The Zn environments are essentially invariant in all of the glass samples investigated, despite significant diAerences in glass chemistry and sample homogeneity. The results indicate that tetrahedral Zn in these glasses takes on the role of a weakly bonded network former. As ZnO is added to a silicate glass, Zn tetrahedra most likely link to silicate tetrahedra, decrease the volume of voids between linked tetrahedra, and restrict diAusion of large ions. These inferences concur with observations that leach rates are reduced for zirconium borosilicate glass as ZnO is added. ” 2000 Elsevier Science B.V. All rights reserved.

Zirconium X-ray absorption spectroscopic (XAS) data were collected and analyzed for a series of zirconia borosilicate glasses developed as potential formulations for immobilization of nuclear fuel reprocessing wastes. For the first time, XAS are presented for silicate glasses with zirconia concentrations as high as 21 wt% and for zektzerite (LiNaZrSi6O15), a crystalline standard that is chemically similar to the glasses. Two other glass series were investigated where the CaO and ZnO contents were varied individually, while the Zr content was held constant. The analysis results indicate that Zr4+ is predominantly in octahedral sites in the glasses. Trends in the data also show that the Zr environments in the glasses are sensitive to changes in ZrO2 concentration, but are less sensitive to changes in Zn or Ca content. With addition of zirconia, the Zr site population shifts from mostly six-coordinated with minor amounts of seven-coordinated Zr, to having a larger fraction of seven-coordinated Zr sites, while maintaining a majority of octahedral Zr. The seven-coordinated Zr atoms probably act as nucleation sites in the glass; as the zirconia content increases to 15 wt% and higher, the numbers of these sites become large enough to promote ZrO2 baddeleyite crystallization. There is no evidence of Zr–Zr pair correlations, similar to those observed in baddeleyite, in any of the crystal-free glasses.

The iron(III) complex of the Schiff base formed from the condensation of 1 equiv. of trist(2-aminoethyl)amine (tren) and 3 equiv. of 4-methyl-5-imidazolecar☐aldehyde has been synthesized by the reaction of iron(III) methoxide, tren and 4-methyl-5-imidazolecar☐aldehyde in methanol. Fetren(meim)3 is low spin as indicated by magnetic moment, Mo¨ssbauer and ESR measurements. The crystal structure of Fetren(meim)3 was determined (space group Pna21, R1 = 0.0331 and wR2 = 0.0857). The complex is six-coordinate although the ligand is potentially heptadentate. Basicity of the three ‘backside’ imidazolate nitrogens is demonstrated in the crystal structure by H-bonding interactions and in solution by reactions with acidic metal complexes. ZnTPP and M(hfa)2 (M = Cu(II), Ni(II)), to give imidazolate bridged adducts. Products of the reaction of Fetren(meim)3 with M(hfa)2 were isolated and identified as the 1:1 adducts.

This report describes the results of work and testing specified by the Test Specifications (24590-LAW-TSP-RT-01-013 Rev.1 and 24590-WTP-TSP-RT-02-001 Rev.0), Test Plans (VSL-02T4800-1 Rev.1 & TP-RPP-WTP-179 Rev.1), and Text Exception (24590-WTP-TEF-RT-03-040). The work and any associated testing followed established quality assurance requirements and conducted as authorized. The descriptions provided in this test report are an accurate account of both the conduct of the work and the data collected. Results required by the Test Plans are reported. Also reported are any unusual or anomalous occurrences that are different from the starting hypotheses. The test results and this report have been reviewed and verified.

This report describes the results of testing specified by the Test Plan VSL-06R6900-1 Rev 0. The work was performed in compliance with quality assurance requirements specified in the Test Plan. Results required by the Test Plan are reported. The test results and this report have been reviewed for correctness, technical adequacy, completeness, and accuracy.

This report describes the results of work and testing specified by Test Specifications 24590-LAW-TSP-RT-04-004, Rev. 0, Test Plans VSL-05T5480-1, Rev. 0 and Text Exceptions 24590-LAW-TEF-RT-05-00002. The work and any associated testing followed established quality assurance requirements and was conducted as authorized. The descriptions provided in this test report are an accurate account of both the conduct of the work and the data collected. Results required by the Test Plan are reported. Also reported are any unusual or anomalous occurences that are different from the starting hypotheses. The test results and this report have been reviewed and verified.

This report describes the results of testing specified by Test Plan VSL-05R5900-1 Rev.0. The work was performed in compliance with the quality assurance requirements specified in the Test Plan. Results required by the Test Plan are reported. The test results and this report have been reviewed for correctness, technical adequacy, completeness, and accuracy.

The principal objective of this work was to extend the glass formulation methodology developed in the earlier work [2, 5, 6] for Envelope A, B and C waste compositions for development of compliant glass compositions targeting five high sodium-sulfur waste loading regions. This was accomplished through a combination of crucible-scale tests, and tests on the DM10 melter system. The DM10 was used for several previous tests on LAW compositions to determine the maximum feed sulfur concentrations that can be processed without forming secondary sulfate phases on the surface of the melt pool. This melter is the most efficient melter platform for screening glass compositions over a wide range of sulfate concentrations and therefore was selected for the present tests. The tests were conducted to provide information on melter processing characteristics and off-gas data, including sulfur incorporation and partitioning. As described above, the main objective was to identify the limits of waste loading in compliant glass formulations spanning the range of expected Na{sub 2}O and SO{sub 3} concentrations in the LAW glasses.

The principal objective of the work described in this Final Report is to extend the glass formulation methodology developed in the earlier work by development of acceptable glass compositions for four LAW compositions specified by ORP that cover the range of sulfate to sodium and potassium to sodium ratios expected in Hanford LAW. The glass formulations were designed to exclude titanium and iron as glass former additives, while tin and vanadium as glass former additives were evaluated for beneficial effects in increasing waste loading in the glasses. This was accomplished through a combination of crucible-scale tests and tests on the DM10 melter system. This melter is the most efficient melter platform for screening glass compositions over a wide range of sulfate concentrations and therefore was selected for the present tests. The current tests provide information on melter processing characteristics and off-gas data, including sulfur incorporation and partitioning.

The objectives of this work are aimed at the development of enhanced LAW propertycomposition models that expand the composition region covered by the models. The models of interest include PCT, VHT, viscosity and electrical conductivity. This is planned as a multi-year effort that will be performed in phases with the objectives listed below for the current phase.  Incorporate property- composition data from the new glasses into the database.  Assess the database and identify composition spaces in the database that need augmentation.  Develop statistically-designed composition matrices to cover the composition regions identified in the above analysis.  Prepare crucible melts of glass compositions from the statistically-designed composition matrix and measure the properties of interest.  Incorporate the above property-composition data into the database.  Assess existing models against the complete dataset and, as necessary, start development of new models.

The radioactive tank waste treatment programs at the U. S. Department of Energy (DOE) have featured joule heated ceramic melter technology for the vitrification of high level waste (HLW). The Hanford Tank Waste Treatment and Immobilization Plant (WTP) employs this same basic technology not only for the vitrification of HLW streams but also for the vitrification of Low Activity Waste (LAW) streams. Because of the much greater throughput rates required of the WTP as compared to the vitrification facilities at the West Valley Demonstration Project (WVDP) or the Defense Waste Processing Facility (DWPF), the WTP employs advanced joule heated melters with forced mixing of the glass pool (bubblers) to improve heat and mass transport and increase melting rates. However, for both HLW and LAW treatment, the ability to increase waste loadings offers the potential to significantly reduce the amount of glass that must be produced and disposed and, therefore, the overall project costs. This report presents the results from a study to investigate several glass property issues related to WTP HLW and LAW vitrification: crystal formation and settling in selected HLW glasses; redox behavior of vanadium and chromium in selected LAW glasses; and key high temperature thermal properties of representativemore » HLW and LAW glasses. The work was conducted according to Test Plans that were prepared for the HLW and LAW scope, respectively. One part of this work thus addresses some of the possible detrimental effects due to considerably higher crystal content in waste glass melts and, in particular, the impact of high crystal contents on the flow property of the glass melt and the settling rate of representative crystalline phases in an environment similar to that of an idling glass melter. Characterization of vanadium redox shifts in representative WTP LAW glasses is the second focal point of this work. The third part of this work focused on key high temperature thermal properties of representative WTP HLW and LAW glasses over a wide range of temperatures, from the melter operating temperature to the glass transition.« less

The major objective of the baseline glass formulation work was to develop and select glass formulations that are compliant with contractual and processing requirements for each of the LAW waste streams. Other objectives of the work included preparation and characterization of glasses with respect to the properties of interest, optimization of sulfate loading in the glasses, evaluation of ability to achieve waste loading limits, testing to demonstrate compatibility of glass melts with melter materials of construction, development of glass formulations to support ILAW qualification activities, and identification of glass formulation issues with respect to contract specifications and processing requirements.

The present report describes the first steps in the development of a glass property-composition database for WTP LAW and HL W glasses that includes all of the data that were used in the development of the WTP baseline models and all of the data collected subsequently as part of WTP enhancement studies perfonned for ORP. The data were reviewed to identifY some of the more significant gaps in the composition space that will need to be filled to support waste processing at Hanford. The WTP baseline models have been evaluated against the new data in terms of range of validity and prediction perfonnance.

Melter tests were conducted to determine the retention of technetium and other volatiles in glass while processing simulated Low Activity Waste (LAW) streams through a DM10 melter equipped with a prototypical off-gas system that concentrates and recycles fluid effiuents back to the melter feed. To support these tests, an existing DM10 system installed at Vitreous State Laboratory (VSL) was modified to add the required recycle loop. Based on the Hanford Tank Waste Treatment and Immobilization Plant (WTP) LAW off-gas system design, suitably scaled versions of the Submerged Bed Scrubber (SBS), Wet Electrostatic Precipitator (WESP), and TLP vacuum evaporator were designed, built, and installed into the DM10 system. Process modeling was used to support this design effort and to ensure that issues associated with the short half life of the {sup 99m}Tc radioisotope that was used in this work were properly addressed and that the system would be capable of meeting the test objectives. In particular, this required that the overall time constant for the system was sufficiently short that a reasonable approach to steady state could be achieved before the {sup 99m}Tc activity dropped below the analytical limits of detection. The conceptual design, detailed design, flow sheet development, process modelmore » development, Piping and Instrumentation Diagram (P&ID) development, control system design, software design and development, system fabrication, installation, procedure development, operator training, and Test Plan development for the new system were all conducted during this project. The new system was commissioned and subjected to a series of shake-down tests before embarking on the planned test program. Various system performance issues that arose during testing were addressed through a series of modifications in order to improve the performance and reliability of the system. The resulting system provided a robust and reliable platform to address the test objectives.« less

In some vitrification processes, the nuclear waste is first mixed with glass-forming additives to form an intermediate aqueous slurry before being processed through a melter at high temperature (typically 1100-1200°C) to form a glass of the desired composition and properties. The rheological characteristics of such an intermediate melter feed slurry are important for the mixing and transport of the feed slurry to the melter and also in the spreading of the slurry on the surface of the glass melt. In this paper, the effects of aging and temperature on the rheological properties of melter feed slurries have been investigated for various high-sodium waste streams. The apparent viscosity of the melter feeds increases significantly with aging time for relatively high solid content melter feeds. After an aging time of 30 days, the apparent viscosity increased exponentially with solid content. A temperature increase from 25°C to 40°C reduced the apparent viscosity with the reduction becoming more evident at high solids content.