Modeling of Hanford Double-Shell Tank Waste Simulants · pH-OLI (20oC) 11.5 pH-meter 1:1 mixture by...
Transcript of Modeling of Hanford Double-Shell Tank Waste Simulants · pH-OLI (20oC) 11.5 pH-meter 1:1 mixture by...
DNV GL © 2014 SAFER, SMARTER, GREENER DNV GL © 2014
Sandeep Chawla and Narasi Sridhar
Modeling of Hanford Double-Shell Tank Waste Simulants
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OLI Simulation Conference 2014
21-22 October, 2014, Florham Park, NJ
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Background
Hanford Site in southeastern Washington State
– Storage of 55 million gallons of radioactive and chemically hazardous wastes
– From weapons production in WWII and Cold War
Waste stored in 177 underground carbon steel storage tanks
– 149 single shell tanks – SSTs (0.55 to 1M gallon capacity)
– Constructed 1943-1964
– 28 double shell tanks – DSTs (1M gallon capacity)
– Constructed 1968-1986
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Background information: J. A. Beavers et al., “SCC of Carbon Steel in Nitrate Based
Hanford Waste Simulants,” presentation at CORROSION 2014, San Antonio, TX, March
2014.
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Background
US DOE, Office of River Protection responsible
Current plan
– Transfer wastes from SSTs to DSTs over next 25 years
– Retrieve wastes from DSTs
– Vitrify into glass logs for repository storage
– Close tanks by 2048
Great emphasis on maintaining integrity of both types of tanks
Management of DSTs important for transfer of wastes from SSTs
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Background
Nitric acid was neutralized with sodium hydroxide and sodium carbonate
– Primarily nitrate based alkaline wastes
– Some carbonate based wastes
Tanks have three phases
– Supernatant liquid
– Saltcake layer consisting of precipitated salts
– Sludge consisting of metal oxides with an interstitial liquid
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Waste leakage
67 SSTs are considered possible leakers
– 750,000 gallons of waste leaked into soils
– Waste discharge to SSTs stopped in 1980
– Pumpable liquid transferred to DSTs
– Saltcake and sludge being transferred to DSTs
Cause of leaks not established
– SCC likely cause for some tanks
– High nitrate concentrations
– Elevated temperature
– Lack of stress relief of weld
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Chemistry limits for corrosion control
Research at SRNL and Hanford
established safe waste chemistry
limits for preventing pitting corrosion
and SCC
– Nitrate concentration determines
whether pitting or SCC is concern
– Maintain adequate levels of
hydroxide and nitrite, which are
inhibitors
– Increase inhibitor concentrations
to offset increasing nitrate
concentration from waste transfers
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B. J. Wiersma and K. H. Subramanian, “Corrosion Control Measures for Liquid Radioactive Waste Storage Tanks at the Savannah River Site,” SRNL-STI-2012-00745, Savannah River National Laboratory, 2012.
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Double Shell Tank DST-AY-102
Tank AY-102
First double-shell radioactive waste storage tank constructed at Hanford
1 million gallon capacity
Completed in 1970, commissioned in 1971
Currently stores hot feed for the vitrification plant
In August 2012, accumulation of radioactive material discovered at two locations
on the floor of the annulus separating primary and secondary liners
– Leak volume estimated between 190 to 520 gallons
– Significant portion of liquid evaporated
– 20 to 50 gallons of drying waste
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AY-102 construction
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J.K Engeman et al., “Tank 241-AY-102 Leak Assessment Report,” RPP-ASMT-53793, Rev. 0, Washington River Protection Solutions, 2012.
Secondary liner • height: 39 ft.-8 in. • bottom diameter: 80 ft. • wall thickness: ¼ in. • Width of annular space
between primary and secondary liners: 2½ ft.
Construction • Primary tank • Secondary liner structure • Concrete shell • Refractory insulating pad
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AY-102 leak assessment
Leak assessment team formed
Consensus agreement
– Radioactive waste on annulus floor was result of breach of primary liner
– Probable leak cause
– corrosion at high temperatures in the tank
– containment margins reduced by construction difficulties and trial-and-error-
repairs leaving residual stresses in the bottom of the primary liner
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Secondary liner concerns
Current concerns
– Effect of leaked waste on integrity
– Estimated life
Focus of ongoing corrosion studies at DNV GL
– Localized corrosion: pitting, LAI corrosion
– Stress corrosion cracking: susceptibility, crack growth rate
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Waste Simulants
Waste simulants used for corrosion and SCC testing of tank steel
Represent environments likely to be present on the floor of the annulus
– Liquid
– Semi-solid
Simulant chemistry developed through
– Analytical information from waste samples
– Thermodynamic modeling (OLI)
– Laboratory trials
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Waste simulant chemistry
Start with non-radioactive, in-tank chemistry
Atmospheric CO2 equilibration calculation
Partial drying/evaporation calculation
Select bounding conditions of pH, temperature
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AY-102 in-tank waste composition
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• A.R. Felmy, O. Qafoku, “Drying of Hanford Tank AY-102 Waste Compositions: Thermodynamic Modeling Results,” PNNL-22758, September 2013.
• Initial CO2 equilibration and evaporation calculations using OLI done at PNNL
• Certain solution compositions exhibited precipitation and required further investigation.
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Development of liquid simulant recipes
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• Derived recipe for partially dried, atmospheric-CO2 equilibrated waste simulant recipe through OLI
• Determined composition of crystalline precipitates by XRD • Made adjustments to obtain precipitate-free, homogeneous
simulants
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Atmospheric CO2 equilibration of 50S:50IL mixture
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OLI survey calculation • Determine CO2 in aqueous phase that is in equilibrium with 300-ppm CO2 in
vapor phase at 50oC. • Determine pH of the waste composition
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Partial drying of CO2-equilibrated 50S-50IL mixture
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Source Chemical Amount in
1-L solution
Calcium chloride 0.012 g
Potassium nitrate 266.975 g
Sodium nitrite 225.288 g
Sodium nitrate 264.719 g
Sodium acetate trihydrate 35.449 g
Sodium chloride 8.456 g
Sodium carbonate 43.031 g
Sodium bicarbonate 5.828 g
Sodium chromate(VI) tetrahydrate 2.364 g
Sodium fluoride 2.234 g
Sodium orthophosphate hydroxide
dodecahydrate 2.734 g
Sodium hydrogen orthophosphate
heptahydrate 40.373 g
Sodium metasilicate nonahydrate 0.039 g
Sodium sulfate 1.463 g
Sodium oxalate 0.838 g
Simulant recipe developed through OLI by
CO2-equilibration and drying to 41 mass%
water (41.A)
OLI
calculation
pH @
50oC
Solids @ 50oC g
MSE 10.7
Sodium chromate decahydrate
3.45
Fluorapatite 0.011
Aqueous 10.0
Potassium nitrate 34.47
Sodium fluoride sulfate
0.71
Sodium oxalate 0.03
Fluorapatite 0.011
Important differences observed in OLI predictions using MSE and Aqueous databanks: • pH • Solids
• amount • composition
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Simulant Preparation in the lab
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Precipitate
Interface
Simulant: 41.A (OLI calculated)
Precipitation @ 50oC
pH MSE
pH Aq
pH meter
Yes 10.7 10.0 9.9
XRD Analysis of Crystalline Components of Precipitate
Component
Natratine NaNO3
Trona Na3H(CO3)2∙2(H2O)
Niter KNO3
Natrophosphate Na7F(PO4)2∙19(H2O)
Partially dried, CO2-equilibrated 50S-50IL mixture
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Preparation of homogeneous simulant
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Simulant: 41.B (41.A minus oxalate, phosphate, fluoride)
Precipitation @ 50oC
pH MSE
pH Aq pH
meter
No 10.7 10.1 10.2
Simulant: 41.C (41.A minus 40 g/L KNO3)
Precipitation @ 50oC
pH MSE
pH Aq
pH meter
No 10.6 10.0 9.7
Simulant: 41.D (41.A minus oxalate, phosphate, fluoride and 40 g/L
KNO3)
Precipitation @ 50oC
pH MSE
pH Aq
pH meter
No 10.5 10.1 10.0
Simulant of partially dried,
CO2-equilibrated 50S-50IL mixture
ADJUSTMENTS
Simulant 41.B preferred for corrosion testing as it did not involve reduction of nitrate content
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Modeling of semi-solid waste simulants
Simulant of partially dried, semi-solid
waste observed on annulus floor
termed as “poultice”
Formulation developed from
analytical information on annulus
waste sample
Carbonate/Bicarbonate ratio adjusted
at constant TIC (total inorganic
carbon) through OLI calculation to
achieve target pH of 11
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Source Chemical mol
Water 10.172
Potassium nitrate 0.997
Sodium chromate(VI) tetrahydrate 0.006
Sodium aluminate 0.349
Sodium carbonate 2.888
Sodium nitrite 1.276
Sodium nitrate 1.922
Sodium fluoride 0.045
Sodium hydrogen orthophosphate heptahydrate 0.022
Sodium metasilicate nonahydrate 0.047
Sodium oxalate 0.034
Sodium formate 0.068
Sodium chloride 0.040
Sodium sulfate 0.011
Sodium bicarbonate 0.704
pH-OLI (20oC) 11.5
pH-meter 1:1 mixture by weight with DI water (~25oC) 10.82
pH-meter 1:1puddle by weight with Equilibrium Liquid (~29oC) 10.51
pH-OLI (50oC) 11.0
Composition of poultice simulant
Appearance of
poultice simulant
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Puddle
Various degrees of wetness of
semi-solid waste simulated by
adding “equilibrium liquid” to
poultice
Equilibrium liquid composition
determined through OLI
calculation
Mixture of poultice and equilibrium
liquid termed as “puddle”
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Mix poultice and equilibrium
liquid recipes. Check pH and
composition of puddles
Original poultice recipe
calculated from
analytical information
in RPP-RPT-54071
Adjust CO3/HCO3
until poultice pH
equal to 11
pH-11 poultice
recipe
pH-11 equilibrium
liquid recipe
Extract aqueous
stream
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Mixer calculation for puddle formulation
Equilibrium liquid pH-11 poultice
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Corrosion testing with waste simulants
Corrosion and SCC testing of AAR TC128 steel
Localized corrosion studies
– Pitting
– Cyclic potentiodynamic polarization
– ASTM G192 (Tsujikawa-Hisamatsu Electrochemical) test
– Long-term coupon immersion
– LAI corrosion
– Multi-electrode array
– Partial coupon immersion
SCC studies
– Slow strain rate tests
– Crack growth rate studies
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Summary
Leakage of radioactive waste from primary liner of tank AY-102 has raised
concerns about integrity of secondary liner
Corrosion and SCC studies ongoing on liner steel using waste simulants
Formulation of waste simulants developed using OLI modeling, analytical
information, and laboratory trials
Important differences observed in predictions using MSE and Aqueous databanks
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Future work
At present, OLI corrosion predictions do not match experimental observations for:
– Polarization curves
– OCP
– Repassivation potential
Further work is needed here as OLI could be used in future risk assessments
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Acknowledgments
The work is being performed under sub-contract No. 53247 with Washington
River Protection Solutions, LLC in support of the U.S. Department of Energy.
The discussions with Kayle Boomer, Ted Venetz, Donald Camaioni, Leon Stock,
Bruce Wiersma, Russ Jones, and Scott Lillard in formulating the test plans and
simulant chemistries are gratefully acknowledged.
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