Modeling of Hanford Double-Shell Tank Waste Simulants

Transcription

1 Modeling of Hanford Double-Shell Tank Waste Simulants OLI Simulation Conference October, 2014, Florham Park, NJ Sandeep Chawla and Narasi Sridhar 1 SAFER, SMARTER, GREENER

2 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 double shell tanks DSTs (1M gallon capacity) Constructed 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

3 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 3

4 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 4

5 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 5

6 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 B. J. Wiersma and K. H. Subramanian, Corrosion Control Measures for Liquid Radioactive Waste Storage Tanks at the Savannah River Site, SRNL-STI , Savannah River National Laboratory,

7 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 7

8 AY-102 construction Construction Primary tank Secondary liner structure Concrete shell Refractory insulating pad 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. J.K Engeman et al., Tank 241-AY-102 Leak Assessment Report, RPP-ASMT-53793, Rev. 0, Washington River Protection Solutions,

9 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-errorrepairs leaving residual stresses in the bottom of the primary liner 9

10 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 10

11 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 11

12 Waste simulant chemistry Start with non-radioactive, in-tank chemistry Atmospheric CO 2 equilibration calculation Partial drying/evaporation calculation Select bounding conditions of ph, temperature 12

13 AY-102 in-tank waste composition Initial CO 2 equilibration and evaporation calculations using OLI done at PNNL Certain solution compositions exhibited precipitation and required further investigation. A.R. Felmy, O. Qafoku, Drying of Hanford Tank AY-102 Waste Compositions: Thermodynamic Modeling Results, PNNL-22758, September

14 Development of liquid simulant recipes Derived recipe for partially dried, atmospheric-co 2 equilibrated waste simulant recipe through OLI Determined composition of crystalline precipitates by XRD Made adjustments to obtain precipitate-free, homogeneous simulants 14

15 Atmospheric CO 2 equilibration of 50S:50IL mixture OLI survey calculation Determine CO 2 in aqueous phase that is in equilibrium with 300-ppm CO 2 in vapor phase at 50 o C. Determine ph of the waste composition 15

16 Partial drying of CO 2 -equilibrated 50S-50IL mixture Source Chemical Amount in 1-L solution Calcium chloride g Potassium nitrate g Sodium nitrite g Sodium nitrate g Sodium acetate trihydrate g Sodium chloride g Sodium carbonate g Sodium bicarbonate g Sodium chromate(vi) tetrahydrate g Sodium fluoride g Sodium orthophosphate hydroxide dodecahydrate g Sodium hydrogen orthophosphate heptahydrate g Sodium metasilicate nonahydrate g Sodium sulfate g Sodium oxalate g Simulant recipe developed through OLI by CO 2 -equilibration and drying to 41 mass% water (41.A) OLI calculation 50 o C MSE 10.7 Aqueous o C Sodium chromate decahydrate g 3.45 Fluorapatite Potassium nitrate Sodium fluoride sulfate 0.71 Sodium oxalate 0.03 Fluorapatite Important differences observed in OLI predictions using MSE and Aqueous databanks: ph Solids amount composition 16

17 Simulant Preparation in the lab Partially dried, CO 2 -equilibrated 50S-50IL mixture XRD Analysis of Crystalline Components of Precipitate Component Precipitate Interface Natratine NaNO 3 Trona Na 3 H(CO 3 ) 2 2(H 2 O) Niter KNO 3 Natrophosphate Na 7 F(PO 4 ) 2 19(H 2 O) Simulant: 41.A (OLI calculated) 50 o C ph MSE ph Aq ph meter Yes

18 Preparation of homogeneous simulant Simulant of partially dried, CO 2 -equilibrated 50S-50IL mixture ADJUSTMENTS Simulant: 41.B (41.A minus oxalate, phosphate, fluoride) 50 o C ph MSE ph Aq ph meter No Simulant: 41.D (41.A minus oxalate, phosphate, fluoride and 40 g/l KNO 3 ) 50 o C ph MSE ph Aq ph meter No Simulant 41.B preferred for corrosion testing as it did not involve reduction of nitrate content Simulant: 41.C (41.A minus 40 g/l KNO 3 ) 50 o C ph MSE ph Aq ph meter No

19 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 Appearance of poultice simulant Composition of poultice simulant Source Chemical mol Water Potassium nitrate Sodium chromate(vi) tetrahydrate Sodium aluminate Sodium carbonate Sodium nitrite Sodium nitrate Sodium fluoride Sodium hydrogen orthophosphate heptahydrate Sodium metasilicate nonahydrate Sodium oxalate Sodium formate Sodium chloride Sodium sulfate Sodium bicarbonate ph-oli (20 o C) 11.5 ph-meter 1:1 mixture by weight with DI water (~25 o C) ph-meter 1:1puddle by weight with Equilibrium Liquid (~29 o C) ph-oli (50 o C)

20 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 Original poultice recipe calculated from analytical information in RPP-RPT Adjust CO 3 /HCO 3 until poultice ph equal to 11 Extract aqueous stream ph-11 poultice recipe ph-11 equilibrium liquid recipe Mix poultice and equilibrium liquid recipes. Check ph and composition of puddles 20

21 Mixer calculation for puddle formulation Equilibrium liquid ph-11 poultice 21

22 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 22

23 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 23

24 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 24

25 Acknowledgments The work is being performed under sub-contract No 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. 25

26 SAFER, SMARTER, GREENER 26