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The Behavior of Radionuclides and RCRA Elements in Tank Backfill Grouts

The Behavior of Radionuclides and RCRA Elements in Tank Backfill Grouts. Mark Fuhrmann, Jeffrey Gillow, and John Heiser Environmental Sciences Department Brookhaven National Laboratory. Environmental Sciences Department Environmental Research and Technology Division.

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The Behavior of Radionuclides and RCRA Elements in Tank Backfill Grouts

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  1. The Behavior of Radionuclides and RCRA Elements in Tank Backfill Grouts Mark Fuhrmann, Jeffrey Gillow, and John Heiser Environmental Sciences Department Brookhaven National Laboratory Environmental Sciences Department Environmental Research and Technology Division

  2. 1966-1972, Nuclear Fuel Services at West Valley reprocessed spent nuclear fuel rods. 1996-2003, vitrified 600,000 gallons of HLW, 277 glass waste forms-2.5 tons each, 24 million Curies. Tanks need to be decommissioned History of HLW Processing at West Valley

  3. HLW tanks and several cells for HLW processing are heavily contaminated. Most wastes to be shipped off-site Tanks and cells may be partially filled with removable grout for interim stabilization and shielding; with enough stability and retention capacity if DOE decides to leave it in place! Long-Term Disposition?

  4. Grout 21: 7.6 % cement, 32.6% fly ash, 10% zeolite, 12.5% slag, 37.2% water. Grout 26: 8.8 % cement, 42.2 % fly ash, 12.0% apatite, 13.0% slag, 23.9% water. Grout Formulations Are these formulations optimal or can they be made to better sequester contaminants?

  5. Isotherms over several orders of magnitude: bracketing waste concentrations for 23 elements What components of the grout provide best retention? Determine Kd and begin to look at mechanisms Long-term condition of grout is fractured and has water moving through it. Assume water contains oxygen Predicted speciation with Geochemist's Workbench. constants NEA Thermochemical Database Project and published reviews (Guillaumont et al., 2003). What is the long-term performance of these materials? Characterize retention of contaminants in the two Grouts

  6. Zeolite sorbs 85Sr readily even with competing ions of Ca in the contact solution. Kd = Concentration in Solid Concentration in Liquid Zeolite in grout improved Sr Retention in Grout 21. G-21 Kd=110 G-26 Kd= 60

  7. Uptake of Tc is very low, less than one in both grouts. Blast furnace slag does remove more Tc than other materials, but the linear isotherm implies adsorption, not precipitation.

  8. Uptake on cement is significant, but on no other materials. Sorption of 125I on grouts is very weak. Very low retention on grouts implies competition

  9. Can be measured and can be significantly different. e.g. 125I sorbs weakly on grout, Kd around 0.7 Cement sorbs a lot of 125I, with Kd around 200, all other materials are much lower. If better sequestration of I is needed, then more cement in the grout mix is worth trying. Sorption of contaminants on different components of the grouts:

  10. Batch Experiments 550 days aging 55 g Ca/K OH contact solution 2 g grout or components Then KHCO3 added incrementally Flow-through Column Experiments Simulated groundwater Ran for about 1000 pore volumes Uranium Behavior in Contact with Grouts

  11. U in solution in batch experiments as KHCO3 is added: cement Keeping pH above 11.5 helps retain U even with high KHCO3

  12. Two grouts behave differently after aging. Presence of the fluorapatite causes U to be released from G-26 after aging and KHCO3 added. The two data points that are off-scale are from Grout-26.

  13. Long-Term batch Experiments (no KHCO3 added) Slowly Grew Calcite Crystals Containing U, Pb, As, and Se Single crystal XRD done at SUNY-SB by Aaron Celestian

  14. Flow through Uranium experiments set up for tritium slug test to determine pore volumes

  15. U (ppb) in Column Effluent pH = 8 pH=12.4 Time water was simulated site groundwaterflow rate was about 200 mL /day; 10 pore-volumes/day.

  16. Column Mass of U in Column (mg) Mass of U leached (mg) % U leached G-21 6.74 0.665 9.7 G-26 7.27 0.496 6.8 Uranium Leached from Columns

  17. Calcite formed in the columns Fe remains with the grout, As is mobilized from the grout and is incorporated into calcite. So is U and Se. image Grout 21, no U As Fe Ca Synchrotron Microprobe : spot size 10 micrometers NSLS X-27a

  18. As U Fe Elemental Distributions in Calcite Grown in HLW Tank Backfill grouts Column experiments, west valley grout G-21, 1000 pore volumes X-27A, NSLS, M. Fuhrmann

  19. Primary sequestration of contaminants takes place on different components of the grouts. Batch experiments imply that high pH minimizes U concentrations even with high KHCO3. In column experiments U in solution was less than 70 ppb for both grouts. Grout 21- 9.7% of U leached. Grout 26- 6.8% of U leached. U, As, and Se are incorporated in calcite as grouts weather. Conclusions

  20. Acknowledgements Funded by DOE through the West Valley Nuclear Services Co. Dan Westcott, program manager, Washington Group Int. Some activities supported by DOE through the Center for Environmental Molecular Sciences, a DOE/NSF center. Thanks to Richard Reeder, John Parise, David Frumberg, Jenny Huang, Aaron Celestian,Tony Lanzirotti (X-26A), Paul Northrup (X-15A) and James Ablett (X-27A).

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