Thermodynamic Modeling of the In-Drift Chemical Environment of a Potential High-Level Nuclear Waste Repository Using OLI Software

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1 Thermodynamic Modeling of the In-Drift Chemical Environment of a Potential High-Level Nuclear Waste Repository Using OLI Software by Roberto T. Pabalan Center for Nuclear Waste Regulatory Analyses San Antonio, Texas 23rd OLI Users Conference Parsippany, New Jersey October 5 6, 2005

2 Outline of Presentation Background on geologic disposal of high-level nuclear waste (HLW) Thermodynamic modeling of repository seepage water evaporation Thermodynamic modeling of salt deliquescence Summary 2

3 Geologic Disposal of U.S. HLW Potential geologic disposal of HLW at Yucca Mountain (YM), Nevada 70,000 MTHM for disposal ~90% commercial spent nuclear fuel ~10% defense HLW, Naval reactor fuel, Department of Energyowned reactor fuel Engineered and natural barriers to provide isolation for at least 10,000 years 3

Engineered Barrier System Potential YM repository design includes waste packages (WP) and drip shields (DS) Constructed of corrosion resistant materials Expected by DOE to

4 Engineered Barrier System Potential YM repository design includes waste packages (WP) and drip shields (DS) Constructed of corrosion resistant materials Expected by DOE to last at least 10,000 years Aqueous corrosion expected to be primary degradation mechanism Mode and rate of aqueous corrosion will depend on water chemistry and temperature 4

5 In-Drift Water Chemistry Water chemistry will be altered by coupled thermal-hydrological-chemical processes Evaporation processes could form potentially corrosive brines and deposit salts on the WP/DS surfaces Inorganic salts in dusts entrained with ventilation air could deposit on the WP/DS surfaces Deliquescence of inorganic salts could form potentially corrosive brines Deliquescence Brine Seepage H 2 O Waste Package Condensed H 2 O Drip Shield 5

6 Thermodynamic Modeling of In-Drift Chemical Environment Using OLI Software Evaporation of dilute seepage waters Potential range in chemistry of waters contacting DS and WP (corrosive species and corrosion inhibitors) StreamAnalyzer Ver. 1.3 Deliquescence behavior of salts and salt mixtures Time and temperature of brine formation Deliquescence Environmental Simulation Program (ESP) Ver. 7.0, Mixed Solvent Electrolyte (MSE) model H 2 O Brine Evaporation H 2 O Waste Package 6

7 Thermodynamic Modeling of Evaporation StreamAnalyzer vs. Experimental Data Seawater evaporation study (McCaffrey et al., 1987) Morton solar production facility for table salt, halite (Great Inagua Island, Bahamas ) Chemical compositions of evaporating seawater at the plant were determined Production process results in concentration factor ~40 relative to seawater Chemical compositions at higher concentration factors (to ~73) were determined through laboratory evaporation experiments 7

8 Thermodynamic Modeling of Evaporation StreamAnalyzer 1.3 vs. McCaffrey et al. Data Na Mg Cl - Molality 0.1 K + Molality SO Ca HCO Degree of Evaporation Degree of Evaporation 1.0 ph or Ionic Strength (molal) ph Ionic strength a(h 2 O) calc Activity of Water Degree of Evaporation 8

9 Thermodynamic Modeling of Evaporation YM Seepage Water Evaporation Temperature = 110 C; Pressure = 0.85 atm Chemistry of YM unsaturated zone porewaters used as input Assumed seepage water is similar to ambient YM porewaters Neglected interactions with in-drift engineered materials 9

10 Thermodynamic Modeling of Evaporation YM Seepage Water Evaporation (Cont d) YM porewater chemistry data (+) available from U.S. Geol. Survey (Yang et al. 1996,1998,2003) Only selected compositions ( ) were used (29 out of 156 in database) Supplemented by chemical divide approach 2- SO Ca Three brine types: calcium-chloride, neutral, and alkaline HCO CO 3 10

11 Thermodynamic Modeling of Evaporation Results of YM Seepage Water Evaporation Brine Type ph Ca 2+ (moles/kg H 2 O) Na + (moles/kg H 2 O) Brine Type Cl - (moles/kg H 2 O) NO 3 - (moles/kg H 2 O) F - (moles/kg H 2 O) 11

12 Thermodynamic Modeling of Evaporation Results of YM Seepage Water Evaporation (Cont d) Brine Type F - (moles/kg H 2 O) Cl - (moles/kg H 2 O) Brine Type Window of Susceptibility to Localized Corrosion of Alloy 22 Some brines have high Cl and F concentration Most have high ratio of corrosion inhibitors (NO 3, SO 2 4, HCO 3, CO 2 3 ) to corrosive Cl Cl - /Σ(inhibitors*) *(NO 3,SO 4,HCO 3,CO 3 ) Note: High Cl /NO 3 ratio is due to formation of CaNO 3+ and NaNO 3 aqueous complexes, which have uncertain thermodynamic data Chemistry information abstracted into a performance assessment code as probability distribution functions (PDFs) 12

13 Deliquescence of Salts Hygroscopic salts will sorb moisture from humid air (deliquesce) and form potentially corrosive brines At YM, deliquescence relative humidity (DRH) could determine the time and temperature during which brines can form on the DS and WP Relative Humidity (%) WP Temp DRH = 50% Drift RH DRH = 30% Time (years) Susceptibility Susceptibility to Aqueous to Aqueous Corrosion Corrosion Calculated In-Drift Relative Humidity and Waste Package Surface Temperature versus Time T 2 >T 1 T Temperature ( o C) 13

14 Deliquescence of Salts (Cont d) DRH is a function of salt composition and temperature Experimental data available on DRH of single salts (0 to ~100 C; Greenspan, 1977) Sparse data on binary and multicomponent salt mixtures at temperatures relevant to a HLW geologic repository (>80 C) 14

15 Thermodynamic Modeling of Deliquescence Deliquescence relative humidity, DRH, is given by DRH = ph 2 O sat /ph 2 O o where ph 2 O sat is the vapor pressure of a saturated salt solution and ph 2 O o is the vapor pressure of pure water Values of ph 2 O sat and ph 2 O o calculated using ESP Ver. 7.0 (MSE model) 15

16 Thermodynamic Modeling of Deliquescence StreamAnalyzer vs. Experimental Data NaCl-NaNO 3 (90 o C) KNO 3 -NaNO 3 (90 o C) Deliq. Relative Humidity (%) Temperature ( C) KCl NaCl NaNO 3 NaCl+NaNO 3 +KNO 3 % Relative Humidity (a) Calculated (ESP 7.0) Measured (Craig et al., 2004) Liquid NaCl + Liquid NaNO Solid (NaCl + NaNO 3 ) + Liquid X-NaNO 3 % Relative Humidity (b) Calculated (ESP 7.0) Measured (Craig et al., 2004) Liquid KNO 3 + Liquid NaNO 3 + Liquid Solid (KNO 3 + NaNO 3 ) X-NaNO 3 Measured DRH (Yang et al., 2005) vs. ESP 7.0 (MSE) values Measured DRH (Craig et al., 2004) vs. ESP 7.0 (MSE) values. (a) NaCl-NaNO 3, (b) KNO 3 -NaNO 3 16

17 Thermodynamic Modeling of Deliquescence Salt Mixtures in the System Na +,K + //Cl,NO 3 KCl NaCl C 71.3 KCl NaCl KCl C 67.5 NaCl KNO NaNO KNO 3 NaNO 3 60 KCl NaCl KNO NaNO KCl 140 C KCl NaCl NaCl KNO 3 Solubility (mole %) of two-or three-salt mixtures in the quaternary system Na +,K + //Cl,NO3 calculated using ESP 7.0 (MSE). The calculated DRH at selected compositions are superimposed on the curves. NaNO KNO NaNO KNO 3 17 NaNO 3

18 Summary The performance of engineered barriers in the potential YM HLW repository is dependent on in-drift water chemistry OLI software has been applied to thermodynamic modeling of in-drift chemical environment Evaporation of seepage waters Deliquescence of salt mixtures 18

19 Acknowledgment The work presented here was performed by the Center for Nuclear Waste Regulatory Analyses (CNWRA) for the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste Repository Safety, under Contract No. NRC This presentation is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the NRC. 19

Phase Behavior of Aqueous Na K Mg Ca Cl NO 3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

J Solution Chem (2007) 36: 723 765 DOI 10.1007/s10953-007-9145-2 ORIGINAL PAPER Phase Behavior of Aqueous Na K Mg Ca Cl NO 3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling Mirosław S. Gruszkiewicz