Radionuclide Release from Savannah River Site Waste Residual Solids Under Conditions Anticipated Following Tank Closure

Radionuclide Release from Savannah River Site Waste Residual Solids under Conditions Anticipated Following Tank Closure

William D. King Savannah River National Laboratory

Performance and Risk Assessment Community of Practice Annual Technical Exchange Meeting October 30-31, 2018

SRNL-MS-2018-00202 SRNL-MS-2018-00202 Background • High Level Radioactive Waste from nuclear weapons production stored in 51 underground tanks – Canyons dissolved reactor targets in nitric acid and extracted uranium and plutonium – Nitric acid solution neutralized and stored in carbon steel tanks – Wastes contain fission products, target materials, process chemicals – Insoluble metal oxides (sludge) settle in tanks at ~20 weight % insoluble solids (dominant metals: Fe, Al, U, Hg, Th) – Aqueous waste (supernate) concentrated by evaporation

– Less soluble sodium salts precipitate to form salt cake (primarily NaNO3) • Current practice for closing High Level Waste (HLW) tanks at Savannah River Site (SRS) involves: – Waste removal to maximum extent practical by mechanical sluicing and, in some cases, chemical cleaning (sludge/insoluble salt residuals remain) – Disconnecting all transfer lines and tank penetrations – Filling internal tank volume with grout (concrete) • Eight SRS waste tanks closed to date – Closed Tanks: 5F, 6F, 12H, 16H, 17F, 18F, 19F, and 20F • Performance Assessment (PA) modeling of radionuclide release from closed tanks into environment over extended time periods (thousands of years, in some cases) – Based on published solubility data of assumed metal species – Natural infiltrating groundwater exposed to grout fill material and residual waste solids layer within closed tank – Uranium, neptunium, plutonium, technetium, and iodine among most likely contamination risk drivers

2 SRNL-MS-2018-00202 Closed Tank Waste Release Model (Performance Assessment)

pore volume = total pore void volume within grout fill material

environment less basic, increasingly oxidizing with time

Radionuclide-Bearing Porewater Fluid based on assumed Target Test Conditions chemical species and equilibrium conditions Condition Eh (mV) pH

Reduced Region II (RR2) -470 11.1

Oxidized Region II (OR2) +560 11.1

Oxidized Region III (OR3) +680 9.2

SRR-CWDA-2010-00128, Rev. 1

3 SRNL-MS-2018-00202 SRS Waste Tank Residual Solids Tested for Release of Radionuclides

residuals remaining prior to closure activities (grouting)

Tank 18 Tank 12 • Type IV tank - 1.3 Mgal • Type I tank - 0.75 Mgal • Few obstructions • Numerous obstructions including cooling coils • Waste not typical PUREX/HM • Waste includes PUREX, HM, THOREX • Waste removal: mechanical sluicing/sand mantis • Waste removal: mechanical and chemical cleaning • Residual waste volume: ~1000 gallons • Residual waste volume: ~1000 gallons • Currently filled with grout • Currently filled with grout • Radionuclide release testing completed 2016 • Radionuclide release testing completed 2018 (SRNL- (SRNL-STI-2016-00432) STI-2018-00484, Rev. 1)

4 SRNL-MS-2018-00202 Archive Tank 18F Floor Samples

leach test sample

Analysis Samples Received in Shielded Cells

Tank 18F Sample Locations

• Multiple floor samples collected/analyzed Keep from goingspecific for tankinformation floor locations prior to closure on SRNL family colors. • Sample FTF-18-1 selected for testing (maximum values for most radionuclides)

SRNL-STI-2010-00386, Rev. 0

5 SRNL-MS-2018-00202 Archive Tank 12H Floor Samples

Mound/Floor Composite Samples for Characterization Tank 12H Sample Locations

• Multiple sub-samples collected from primaryKeep tank going floor forand information a mound of residual material • Mound and floor samples composited at variouson SRNL ratios family for colors.characterization and leach testing

SRNL-STI-2015-00241, Rev. 0

6 SRNL-MS-2018-00202 Tank Residual Sample Characterization Data

Tank 18F residuals Tank 12H residuals Radionuclide µCi/g Element Wt. % Radionuclide µCi/g Element Wt. % Al 11 Tc-99 3E-2 Al 19 Tc-99 4E-3 Fe 10 I-129 1E-5 Fe 17 I-129 4E-3 U 6 Hg 9 Np-237 9E-03 Np-237 1E-02 Mg 4 Th 6 Pu-238 90 Ca 3 Pu-238 6 Mn 1 Si 2 Pu-239 16 Na 0.6 Pu-239 4 Mn 1 Pu-240 4 U 0.2 Pu-240 1 Total 37 Total 53 Pu-241 16 Pu-241 21

• Tank 12H bulk composition high in Hg and Th and low in U versus Tank 18F • Less Tc-99, Pu-239, and Pu-240 in Tank 12H residuals versus Tank 18F • More I-129 and Pu-238 in Tank 12H residuals versus Tank 18F (higher than anticipated I-129 inventory) • Comparable Np-237 and Pu-241 in the residual tank samples

7 SRNL-MS-2018-00202 SRNL Shielded Cells Facility

• Remote sample handling with manipulators • Gases and probes introducedKeep through going front for wallinformation penetrations on SRNL family colors. • Ambient temperature varies with season/weather

8 SRNL-MS-2018-00202 Three Component Test Samples

1. Grout Porewater Simulant Early testing indicated approaching Component mg/L SRS Infiltrating Water plus: pH and Eh targets under oxidizing Infiltrating Water Na+ 1.4 • CaCO3 added to saturation conditions required simplified system. ‐ representative of Cl 5.5 • Ca(OH)2 to raise pH SRS groundwater Ca2+ 1.0 Mg2+ 0.7 K+ 0.2 Sample Atmosphere 2- SO4 0.7 Leach Test • Continuous air purge to lower pH Sample and maintain oxidizing conditions • Continuous N2 purge to maintain reducing conditions

2. Grout or Grout–Representative Solids 3. Residual Tank Waste Solids

• Ground Cement, Flyash, and Slag (CFS) or CaCO3 • Tank 12H or 18F residuals • FeS to produce reducing Eh • Residuals washed to better represent conditions after closed tank aging

Test method development SRNL-STI-2015-00446, Rev. 0

9 SRNL-MS-2018-00202 Radionuclide Release Test Equipment

Test Rig Glass Test Vessels • Multi-position stir plates • Caustic scrubber for CO2-stripping • Customized water bath with attached • Humidifier to minimize evaporative liquid losses bubbler manifold Keep going for information on SRNL• Leach family vessel colors. for sample atmosphere control • Water bath recirculator with continuous agitation and temperature • Custom glass leach test and gas control treatment vessels

10 SRNL-MS-2018-00202 Sample and Gas Pretreatment Vessel Layout

air supply air supply air supply N2 supply

HM CS CS CT* CT* HM

N2 supply

OR3* Empty HM CT HM RR2B*

OR3* OR2* OR2* RR2* RR2* RR2B*

*outlet to bubbler manifold, Legend flow control achieved with vessel sequence for oxidizing OR2 – Oxidizing Region II vessel valves on manifold samples: CS→HM→ leach OR3 – Oxidizing Region III vessel vessel RR2 – Reducing Region II vessel no caustic scrubber vessel CS = caustic scrubber vessel for reducing conditions HM = humidifier vessel (humidifier only) CT = control vessel

11 SRNL-MS-2018-00202 Leach Test Sample Sub-Sampling System bag to minimize tip contamination 0.1 µm PVDF filter vent

10 mL syringe quick-connect fittings 0.1 µm PVDF filter quick-connect fitting shielded analysis bottles • Substantial background contamination (especially Pu) in shielded cells facility • Leach testing requires measurement of very low radionuclide concentrations (near detectable limits) • System utilized to isolate sub-samples immediately following filtration in analysis bottles; bottles never opened within shielded cells • Cell floor and manipulators cleaned prior to testing and clean cloth wipes placed on floor surface prior to sub-sampling • Additional efforts to minimize contamination from bottle exterior surfaces during analysis • Control sample blanks utilized to evaluate contamination levels

12 SRNL-MS-2018-00202 Installed Equipment within Shielded Cells

• Samples prepared under appropriate atmospheres (CO2-stripped air/N2 purge) • Oxidizing samples washed with groundwater simulant prior to testing • Reducing samples tested in two phasesKeep (washed/unwashed) going for information representing initial and later time periods on SRNL family colors. • Weekly sample collection, two month test duration

• pH and Eh monitored weekly

• pH and Eh adjustments as needed to reach targets

13 SRNL-MS-2018-00202 Issues, Observations, and Lessons Learned During Testing

• General – Sub-sampling system successfully minimized sample contamination

– Target pH values achieved, although Tank 12H solids with CaCO3 gradually consumed base equivalents and required frequent Ca(OH)2 addition

– Target Eh values could not be achieved, although ranges of 0.7 and 0.5 V were observed with Tank 18F and 12H residuals, respectively • Tank 18F – Siphon-induced water bath contamination of one sample occurred (gas system design modified) – Lost most uranium to preliminary wash due to formation of soluble carbonate phase (Cejkaite,

Na4UO2(CO3)3) during air-contact of residual prior to grout addition (timely wash analysis needed; empty tank storage conditions can lead to residual waste chemical changes) • Tank 12H – Could not agitate samples with stir bars during testing – manual daily agitation utilized (preliminary agitation method performance evaluation with actual waste in future testing) – One glass vessel ruptured during testing (vessel design changes may be considered in future testing) – Iodine leaching levels appear to be just below detection (sample size and counting times must be increased to determine if lower detection is possible)

14 SRNL-MS-2018-00202 Leach Test Results

Leachate Molarity Tank 18F Tc data trends Sample Eh pH indicate equilibrium not Tc-99 U Np-237 Pu achieved Tank 18F RRII-CFS -196 11.4 <6E-10 2E-06 <2E-10 7E-11 RRII-CC -208 10.9 <6E-10 2E-06 <2E-10 2E-09 Increasing Tank 18F U data solubility may not represent ORII 340 11.0 1E-08 1E-05 ≤3E-10 3E-09 equilibrium due to wash losses ORIII 507 9.4 8E-09 2E-04 3E-09 8E-09 Leachate Molarity Sample E pH h Tc-99 U Np-237 Pu I-129 RRII-CFS -71 11.3 2E-09 1E-08 <5E-11 <1E-12 <1E-7 Tank 12H RRII-CC -64 11.0 ≤6E-10 9E-09 <5E-11 ≤3E-12 <3E-7 Increasing ORII 341 10.6 9E-09 3E-07 ≤2E-10 1E-10 ≤1E-7 solubility ORIII 405 9.2 6E-09 2E-06 1E-09 1E-10 ≤1E-7 • Tank 12H technetium and neptunium solubility comparable to Tank 18F (exception RRII-CFS) • Tank 12H uranium and plutonium solubility lower than Tank 18F • Tank 12H iodine solubility generally below or near detectable analytical limits

15 SRNL-MS-2018-00202 Predicted Pu and U Residual Solubilities

non-equilibrium with dissolved oxygen impacts Pu solubility

lowest concentrations for co-precipitates

a Eh values represent more realistic, non-equilibrium conditions with dissolved oxygen b Eh values represent equilibrium conditions with dissolved oxygen c apparent solubility based on primary iron phase solubility d Pu solubility based on amorphous plutonium oxide phase

SRNL-STI-2012-00404, Rev. 0

16 SRNL-MS-2018-00202 Predicted Tc, I, and Np Residual Solubilities

a Eh values represent more realistic, non-equilibrium conditions with dissolved oxygen b Eh values represent equilibrium conditions with dissolved oxygen c apparent solubility based on primary iron phase solubility d Np solubility based on hydrous (hyd), aged, and amorphous (am) neptunium oxide and oxyhydroxide phases

SRNL-STI-2012-00404, Rev. 0

17 SRNL-MS-2018-00202 Conclusions

• Leaching studies completed for actual SRS Tank 18F and 12H residual solids • Low leachate metal concentrations (near or below analytical detection limits in some cases) observed with uranium being the most soluble metal analyzed • Discovered significant U losses to wash for Tank 18F oxidizing samples and concentrations of U, Np, and Pu higher than observed in leachate samples (presumably associated with presence of more soluble chemical species as portion of total); losses to wash not significant with Tank 12H residuals • Tank 18F U leachate concentrations were high and significantly exceeded predictions, presumably due to differences between actual and assumed chemical speciation; Tank 12H U exceeded predictions

under reducing conditions by less than order of magnitude (likely associated with Eh well above target) • Other radionuclide concentrations between predictions for co-precipitated iron phases and assumed pure phases under equilibrium conditions with dissolved oxygen (i.e. below maximum PA predictions)

• Tank 12H I-129 solubility much lower than assumed in PA and in range expected for AgI and Hg2I2

18 SRNL-MS-2018-00202 Path Forward and Acknowledgements Path Forward • Simulant lysimeter testing to identify more realistic target conditions • Additional Radionuclide release testing – Tank typical of F Area sludge residuals – H Area sludge residuals not exposed to oxalic acid cleaning Acknowledgements • Savannah River Remediation (funding source) – Mark Layton, Kent Rosenberger, Tim Coffield • Other SRNL Contributors – D. Diprete, M. Malik, M. Jones (analysis) – Rita Sullivan and Jeff Mixon (shielded cell technicians) – K. Roberts (pore water development & initial leaching studies) – K. Taylor-Pashow (actinide and radiochemistry) – D. Miller (pore water development) – C. Langton (cementitious waste forms) – M. Denham (geochemical modeling) – G. Flach (PA Modeling) – D. Kaplan (geochemistry) – L. Oji (tank characterization) – M. Hay (technical reviews)