1. Modeling the DR-A in-situ diffusion experiment (Opalinus Clay): Ionic strength effects on solute transport Josep M. Soler (IDAEA-CSIC, Catalonia, Spain) Carl I. Steefel (LBNL, USA) Olivier X. Leupin (NAGRA, Switzerland) Thomas Gimmi (PSI & Univ. Bern, Switzerland) Mont Terri Project Disturbances, diffusion and retention (DR-A) Nagra, Switzerland NWMO, Canada DOE, USA

2. In-situ diffusion experiments, Mont Terri URL (15 years) DI: HTO, I - DI-A: HTO, I -, 22 Na +, Cs + DI-B: 2 H, I -, 6 Li +, 87 Rb + DI-A2: HTO, I -, Br -, 85 Sr 2+, Cs +, 60 Co 2+, Eu 3+ DR: 2 H, 18 O, 133 Ba 2+, 60 Co 2+, 137 Cs +, Eu 3+, 152 Eu 3+ HTO, Br -, I -, SeO 4 2-, 22 Na +, 85 Sr 2+, Cs + Proven experimental setup Circulation of synthetic solution at equilibrium with rock (OPA) + tracers Data: (1) monitoring (2) rock profiles Successful for conservative and moderately-sorbing tracers Anion exclusion Sorption of cations (Effect of filters) (BDZ) 1 m

3. DR-A: Objectives Induce a perturbation in the system Check the capabilities of reactive transport codes DR-A: Concept (1)Conventional in-situ diffusion experiment (189 days) Synthetic OPA pw + tracers HTO, I -, Br -, Cs +, 85 Sr 2+, 60 Co 2+, Eu 3+ (2) Replace synthetic OPA pw with high-salinity solution 0.5 M NaCl + 0.56 M KCl 85 Sr 2+ Modeling by different teams: PSI, Univ. Bern (T. Gimmi), Univ. British Columbia (U. Mayer, M. Xie), Lawrence Berkeley Natl. Lab. (C. Steefel), IDAEA-CSIC, T. Appelo Nov. 2011 – Nov. 2013

4. Basis: Modeling with CrunchFlow, 1D – radial r = 4.16 cm (circle with same perimeter as ellipse) Excess volume of ca. 1%. Borehole capacity decreased by the same factor for same volume as ellipse. Diffusion domain (bedding plane) x y Borehole Dip = 32.5 o 1D c= concentration in solution [mol. m -3 ] t = time [s] D e = effective diffusion coefficient [m 2. s -1 ] c tot = total concentration of tracer [mol.m -3 ]  = diffusion accessible porosity  d = bulk dry density [kg. m -3 ] s= sorbed tracer conc. [mol. kg -1 ] filter gap

5. Modeling with CrunchFlowMC, 1D – radial All chemical species modeled simultaneously No decay in the model (decay-corrected data) (1)Dynamic calculation of bulk porosity and microporosity (EDL) Microporosity A clay (m 2 /m 3 rock), DL : n. of Debye lenghts Total porosity (fixed) = bulk porosity + microporosity

6. (2) Concentrations in EDL related to concs. in bulk water through the mean electrical potential of the diffuse layer ( ) Mean electrical potential calculated from charge balance between surface charge and diffuse layer. Micropor. (EDL), C i EDL Bulk porosity, C i B

7. Micropor. (EDL), C i EDL Bulk porosity, C i B  = 1 in the rock D 0 = D p (3) Different De values in the microporosity (EDL) and bulk porosity. Nernst-Planck equation

8. run 17b PARAMETERS Borehole: well mixed, D e = 1e-4 m 2 /s,  = 3.262 (tank, lines, inner gap: 10243 mL; Gimmi, 2003, PSI AN 44-13-03) Filter: well mixed, D e = 1e-5 m 2 /s,  = 0.445 Gap: D e = 2e-9 m 2 /s,  = 0.989 Rock: total porosity  = 0.15 Bulk porosity Cations, HTO: D p = 1e-9 m 2 /s Anions: D p = 3e-10 m 2 /s Microporosity (EDL) Cations, HTO: D p = 9e-11 m 2 /s (except Cs +, D p = 1e-9 m 2 /s) Anions: D p = 2e-11 m 2 /s DL = 6 Surf. charge on illite: 0.2 eq/kg (B&B, 2000) (25 vol%, 200 m 2 /g) Sorption of K had to be decreased (logK(PS-K)=-0.4 instead of -1.1) Calculation up to 729 days (final 6-day back-diffusion not included)

9. INITIAL SOLUTION COMPOSITIONS Total concentrations in mol/kg_H 2 O Rock/filter/gapBorehole (1)Borehole (2) T (°C)18 pH7.6 Na + 2.59×10 -1 5.00×10 -1 K+K+ 1.64×10 -3 5.60×10 -1 Mg 2+ 1.80×10 -2 1.47×10 -2 Ca 2+ 1.88×10 -2 2.30×10 -2 Sr 2+ 5.10×10 -4 4.54×10 -4 Cl - 3.00×10 -1 1.12×10 0 charge SO 4 2- 1.37×10 -2 2.37×10 -4 HCO 3 - 7.25×10 -3 charge8.19×10 -3 charge5.63×10 -4 P CO2,atm Cs + 2.00×10 -8 2.069×10 -4 6.23×10 -6 SiO 2 (aq)6.71×10 -5 quartz 5.76×10 -5 quartz Al 3+ 1.18×10 -8 illite 2.88×10 -9 illite I-I- 1.00×10 -12 1.09×10 -2 8.60×10 -3 Br - 7.15×10 -4 1.09×10 -2 8.86×10 -3 40 species in solution

10. CATION EXCHANGE – Opalinus Clay (Bradbury & Baeyens, 2000; Jakob et al., 2009; Van Loon et al., 2009) log K Site capacity (eq/kg) FES-Cs + Na + = FES-Na + Cs + -7-0 1.05×10 -4 FES-K + Na + = FES-Na + K + -2.4 II-Cs + Na + = II-Na + Cs + -3.2 8.4×10 -3 II-K + Na + = II-Na + K + -2.1 PS-Cs + Na + = PS-Na + Cs + -1.6 9.5×10 -2 PS-K + Na + = PS-Na + K + -0.4 (-1.1) PS 2 -Ca + 2 Na + = 2 PS-Na + Ca 2+ -0.67 PS 2 -Mg + 2 Na + = 2 PS-Na + Mg 2+ -0.59 PS 2 -Sr + 2 Na + = 2 PS-Na + Sr 2+ -0.59

11. RESULTS Borehole

12. HTO, I -, Br -

13. Cs +

14. Ca 2+ Mg 2+ Na + K+K+

15. Sr 2+ Cl - SO 4 2- ?

16. RESULTS Rock

17. Model porosities, t = 729 d (total por. = 15%, fixed) EDL Bulk

18. I-I- Aqueous extract data (PSI) HTO Back-diffusion signal (final 6 days)

19. Aqueous extract data (U. Bern) Cl - Br -

20. Ni-en extract data (U. Bern) – exchange complex Prof. 11.60 Prof. 11.80

21. BOREHOLE Good match of borehole concentrations (some overestimation of Cs + right after solution exchange; also problem with SO 4 2- ) Clear effect of increased salinity on anions: Reduced microporosity (EDL), D p (B) > D p (EDL), C B > C EDL Also effect on HTO: D p (B) > D p (EDL) PROFILES – aqueous extracts Anions, HTO: approximate match of profiles, concentrations on the low side Cations: good match for Na +, K + ; no match for Ca 2+, Mg 2+ PROFILES – Ni-en extracts Good match of transport distances and composition of the exchange complex K sorption had to be decreased (logK(PS-K)=-0.4 instead of -1.1) Summary and conclusions Thank you for your attention