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Title: Defense Waste Processing Facility (DWPF) Viscosity Model: Revisions for Processing High TiO 2 Containing Glasses

Abstract

Radioactive high-level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the Defense Waste Processing Facility (DWPF) since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it is poured into ten foot tall by two foot diameter canisters. A unique “feed forward” statistical process control (SPC) was developed for this control rather than statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-composition models form the basis for the “feed forward” SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to guarantee, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository. The DWPF SPC system is known as the Product Composition Control System (PCCS). The DWPF will soon be receiving wastes from the Salt Waste Processing Facility (SWPF) containing increased concentrations of TiO 2, Na 2O, and Cs 2O . The SWPFmore » is being built to pretreat the high-curie fraction of the salt waste to be removed from the HLW tanks in the F- and H-Area Tank Farms at the SRS. In order to process TiO 2 concentrations >2.0 wt% in the DWPF, new viscosity data were developed over the range of 1.90 to 6.09 wt% TiO 2 and evaluated against the 2005 viscosity model. An alternate viscosity model is also derived for potential future use, should the DWPF ever need to process other titanate-containing ion exchange materials. The ultimate limit on the amount of TiO 2 that can be accommodated from SWPF will be determined by the three PCCS models, the waste composition of a given sludge batch, the waste loading of the sludge batch, and the frit used for vitrification.« less

Authors:
 [1];  [1]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Publication Date:
Research Org.:
Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Sponsoring Org.:
USDOE Office of Environmental Management (EM)
OSTI Identifier:
1323882
Report Number(s):
SRNL-STI-2016-00115
TRN: US1601913
DOE Contract Number:
AC09-08SR22470; AC09-96SR18500; AC09-89SR18035
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; HIGH-LEVEL RADIOACTIVE WASTES; WASTE FORMS; BOROSILICATE GLASS; WASTE PROCESSING; TITANIUM OXIDES; PROCESS CONTROL; VITRIFICATION; SAVANNAH RIVER PLANT; HARDNESS; VISCOSITY; MODIFICATIONS; LIMITING VALUES; DWPF; Salt Waste Processing Facility; monosodium titanate; crystalline silicon titanate

Citation Formats

Jantzen, C. M., and Edwards, T. B. Defense Waste Processing Facility (DWPF) Viscosity Model: Revisions for Processing High TiO2 Containing Glasses. United States: N. p., 2016. Web. doi:10.2172/1323882.
Jantzen, C. M., & Edwards, T. B. Defense Waste Processing Facility (DWPF) Viscosity Model: Revisions for Processing High TiO2 Containing Glasses. United States. doi:10.2172/1323882.
Jantzen, C. M., and Edwards, T. B. 2016. "Defense Waste Processing Facility (DWPF) Viscosity Model: Revisions for Processing High TiO2 Containing Glasses". United States. doi:10.2172/1323882. https://www.osti.gov/servlets/purl/1323882.
@article{osti_1323882,
title = {Defense Waste Processing Facility (DWPF) Viscosity Model: Revisions for Processing High TiO2 Containing Glasses},
author = {Jantzen, C. M. and Edwards, T. B.},
abstractNote = {Radioactive high-level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the Defense Waste Processing Facility (DWPF) since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it is poured into ten foot tall by two foot diameter canisters. A unique “feed forward” statistical process control (SPC) was developed for this control rather than statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-composition models form the basis for the “feed forward” SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to guarantee, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository. The DWPF SPC system is known as the Product Composition Control System (PCCS). The DWPF will soon be receiving wastes from the Salt Waste Processing Facility (SWPF) containing increased concentrations of TiO2, Na2O, and Cs2O . The SWPF is being built to pretreat the high-curie fraction of the salt waste to be removed from the HLW tanks in the F- and H-Area Tank Farms at the SRS. In order to process TiO2 concentrations >2.0 wt% in the DWPF, new viscosity data were developed over the range of 1.90 to 6.09 wt% TiO2 and evaluated against the 2005 viscosity model. An alternate viscosity model is also derived for potential future use, should the DWPF ever need to process other titanate-containing ion exchange materials. The ultimate limit on the amount of TiO2 that can be accommodated from SWPF will be determined by the three PCCS models, the waste composition of a given sludge batch, the waste loading of the sludge batch, and the frit used for vitrification.},
doi = {10.2172/1323882},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 8
}

Technical Report:

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  • Radioactive high level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the Defense Waste Processing Facility (DWPF) since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it is poured into ten foot tall by two foot diameter canisters. A unique “feed forward” statistical process control (SPC) was developed for this control rather than statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-compositionmore » models form the basis for the “feed forward” SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to guarantee, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository. This report documents the development of revised TiO 2, Na 2O, Li 2O and Fe 2O 3 coefficients in the SWPF liquidus model and revised coefficients (a, b, c, and d).« less
  • Radioactive high-level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the DWPF since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it has been poured into ten foot tall by two foot diameter canisters. A unique “feed forward” statistical process control (SPC) was developed for this control rather than relying on statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-composition models formmore » the basis for the “feed forward” SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to determine, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository. The DWPF SPC system is known as the Product Composition Control System (PCCS). One of the process models within PCCS is known as the Thermodynamic Hydration Energy Reaction MOdel (THERMO™). The DWPF will soon be receiving increased concentrations of TiO 2-, Na 2O-, and Cs 2O-enriched wastes from the Salt Waste Processing Facility (SWPF). The SWPF has been built to pretreat the high-curie fraction of the salt waste to be removed from the HLW tanks in the F- and H-Area Tank Farms at the SRS. In order to validate the existing TiO 2 term in THERMO™ beyond 2.0 wt% in the DWPF, new durability data were developed over the target range of 2.00 to 6.00 wt% TiO 2 and evaluated against the 1995 durability model. The durability was measured by the 7-day Product Consistency Test. This study documents the adequacy of the existing THERMO™ terms. It is recommended that the modified THERMO™ durability models and the modified property acceptable region limits for the durability constraints be incorporated in the next revision of the technical bases for PCCS and then implemented into PCCS. It is also recommended that an reduction of constraints of 4 wt% Al 2O 3 be implemented with no restrictions on the amount of alkali in the glass for TiO 2 values ≥2 wt%. The ultimate limit on the amount of TiO 2 that can be accommodated from SWPF will be determined by the three PCCS models, the waste composition of a given sludge batch, the waste loading of the sludge batch, and the frit used for vitrification.« less
  • The Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) vitrifies high level liquid waste (HLLW) into borosilicate glass for stabilization and permanent disposal. The viscosity of the borosilicate glass melt as a function of temperature is the single most important variable affecting the melt rate and pour ability of the glass. The viscosity determines the rate of melting of the raw feed, the rate of glass bubble release (foaming and fining), the rate of homogenization, the adequacy of heat transfer, the devitrification rate, and thus, the quality (in terms of glass homogeneity) of the final glass product.more » If the viscosity is too low, excessive convection currents can occur during melting, increasing corrosion/erosion of the melter materials of construction (refractory and electrodes) and making control of the melter more difficult. The lowest glass viscosities allowed in the DWPF melter have, therefore, been determined to be approximately 20 poise. DWPF glasses must pour continuously into a large steel canister for ultimate storage in a geologic repository, but glasses with a viscosity greater than or equal to 500 poise do not readily pour. Moreover, too high a viscosity can reduce product quality by causing voids in the final glass. A conservative range of 20-110 poise at a melt temperature, Tmelt or Tm, of 1150 degrees C was, therefore, established for DWPF production. In summary, a uranium term is not needed in the DWPF viscosity model as long as the U3O8 concentrations of the glasses being melted are less than or equal to 5.76 wt percent, the maximum value examined in this study. The fact that a U-plus-6 term is not needed in the DWPF viscosity model is consistent with the fact that U-plus-6 has four bridging and two non-bridging oxygen bonds. Therefore, the impact of the number of bridging and non-bridging oxygens is approximately equal at U3O8 concentrations of less than or equal to 5.76 wt percent. Uranium may not have an impact at higher U3O8 concentrations but this would have to be demonstrated since the effects of the 0.66:0.33 BO to NBO ratio may become more significant as the U3O8 content increases. While U-plus-6 appears to have little to no impact on glass viscosity, this may or may not be true for U-plus-4 and U-plus-5 in glass since these species were not examined in this study. This is of especial note since the DWPF is currently operating at a REDOX target of 0.2 where 45 percent of the uranium is U-plus-6, 45 percent is U-plus-5, and 10 percent is U-plus-4. An additional 26 glasses for which 98 viscosity-temperature measurements were available indicate disparate roles for ThO2 depending on the U3O8 concentration and the Al2O3 concentration of the glasses measured. For the data generated on three DWPF glasses at SRNL where the ThO2 content and U3O8 content were each in the 2.5-3.0 wt percent range, the presence of ThO2 made the melts more fluid. This is consistent with what is known from the literature about the coordination chemistry of Th-plus-4 in glass, e.g. that it may act as a weak network modifier. However, twenty two West Valley mixed uranium-thorium glasses with U3O8 approximately 0.6-0.7 wt percent and ThO2 of 3.5-3.6 wt percent, demonstrate a trend toward more polymerized melts (higher viscosities). The West Valley glasses are much higher in Al2O3 than the glasses measured at SRNL although they are in the range of the DWPF viscosity model. This indicates that there may be a synergistic interaction between ThO2, U3O8, and Al2O3 that needs further investigation.« less
  • A statistically-designed mixture study was undertaken to determine the effect that compositional variation in simulated Savannah River nuclear waste glass has upon melt surface tension, viscosity and Fe/sup 2 +//Fe/sup 3 +/ equilibria. In each case, linear models adequately predicted these properties from the SiO/sub 2/, B/sub 2/O/sub 3/, Na/sub 2/O, Li/sub 2/O and K/sub 2/O contents of the borosilicate glass. Surface tension at 1150/degree/C increases with increasing SiO/sub 2/ or Li/sub 2/O content, viscosity increases with increasing SiO/sub 2/ content and the Fe/sup 2 +//Fe/sup 3 +/ ratio increases with additions of SiO/sub 2/, B/sub 2/O/sub 3/ or Li/submore » 2/O at constant temperature and partial pressure of oxygen. Addition of the other oxides decreases the values of these properties. Surface tension was additionally found to decrease under more oxidizing melt conditions and with water vapor present in the atmosphere. The Fe/sup 2 +//Fe/sup 3 +/ ratio only changed by 0.05 over the range of compositions tested, which suggests that compositional variation in the vitrification process will likely not adversely affect its use as a monitor of the glass oxidation state. 18 refs., 6 figs., 3 tabs.« less
  • The DWPF melter off-gas systems have two High-Efficiency Mist Eliminators (HEME) upstream of the High-Efficiency Particulates Air filters (HEPA) to remove fine droplets and particulates from the off-gas. The HEMEs consist of three filter candles. Each filter candle consists of a 0.5 inch layer of 30 micron diameter glass fiber on the upstream face followed by a 2.5 inch layer of 8-micron-diameter glass fiber packed at 11 lbs per cubic foot. The coarse 30-micron filter serves as a prefilter and extends the life of the HEME filter. To have an acceptable fitter life and an efficient HEMIE operation, air atomizedmore » water is sprayed into the off-gas stream entering the 14EME and onto the HEMEE surface. The water spray keeps the HEME wet which would dissolve the soluble particulates and enhance the HEME efficiency. A properly designed spray nozzle should wet the three candies of the HEME filter completely.« less