The Unsaturated THM behaviour in porous material - an important issue for a HLW repository

1. The Unsaturated THM behaviour in porous material - an important issue for a HLW repository Li X.L. EIG EURIDICE Exchange - Meeting 6 June 2006

2. Outline • Unsaturated porous media : variables • Main THM coupling processes in unsaturated state • Main unsaturated THM coupling processes • in a rad-waste disposal system • Investigation methods • laboratory tests • in situ tests • numerical modelling • Examples • Conclusion/ Discussion : • The roles of unsaturated THM process for repository design ?

3. Saturated porous media • Two phases porous media : • Solid • water ( dissolved gas) uw > 0, Srw = 100 %

4. Unsaturated porous media clay particle water Sand grain gas • Three phases porous media : • Solid • water ( dissolved gas) • gas ( dry air + water vapour due to T) ug > uw , if ug = 0, uw < 0 Srw < 100 %

5. Unsaturated porous media ! Matrix suction : If saline water : Total suction = matrix suction + osmotic suction

6. Main THM coupling processes in unsaturated state Thermal processes : Heat transfer through 3 phases • water motion Hydraulic processes • gas (dry air + vapour ) motion Mechanical processes: Deformation = f ( stress, suction , temperature ) THM Coupling ! Highly dependent on the suction !

7. Thermal processes : Heat transfer convection Conduction vaporisation G = f (s,n, T )=>(H-T, M-T) Couplings : Convection => H -T Vaporisation – condensation => TH

8. Hydraulic processes : Multiphase flow Convection (water and gas) : generalised Darcy’s law permeability => f(T) Retention curves => f (T)  High non linear problems due to suction !

9. Hydraulic processes : Multiphase flow f, rf f (T) Convection (water and gas) : generalised Darcy’s law T  permeability T  dilation of the fluid  fluid pressure generation • T-H coupling kint = f(n) => M-H coupling

10. Hydraulic processes : Multiphasic flow Diffusion (Vapour and dry air) : Fick’s law Highly depend on s ,T, n => vaporization /condensation Datm : molecular diffusion coefficient : tortuosity

11. Mechanical processes : suction effects Volumetric Deviatoric Shear strength increases Stiffness increases Hardeing,

12. Mechanical processes : suction effects e vert [%] Succion [kPa] • suction variation can induce reversible • and irreversible strains, cracks, etc. • wetting path under different stresses • => swelling / collapse => Microstructures ,

13. Mechanical processes : Temperature effects DT  dilation DT  reversible e T-e  f (s)

14. Mechanical processes : Temperature effects T  softening

15. Mechanical processes : Constitutive law BBM model + T effects : elasticity, softening, etc.

16. Main THM coupling processes in unsaturated state T vaporisation g, rg, , w, rw conduction convection l deformation Kint, Ss H M deformation Complex THM couplings !

17. Unsaturated THM coupling processesin a rad-waste disposal system • Where ? • near field : • EBS (backfill, seal, etc.) • + adjacent Host rock • When ? • Pre-thermal phase : • EDZ around excavation • ventilation of the gallery • hydration of the EBS • swelling, etc. • Thermal phase (before saturation): • evaporation / condensation • hydration of the EBS • etc. SAFIR2 reference concept

18. Unsaturated THM coupling processesin a rad-waste disposal system T vaporisation g, rg, , w, rw conduction convection l deformation Kint, Ss H M deformation • Complexity of THM processes increases • interaction EBS/Host Rock • interface behaviour (skin) • boundary conditions of the system !

19. Scheme of THM processes in the near field s , e s , e From Gens, 2003

20. Coupled phenomena in vapour transport Coupling ( strong/weak) depends on the boundary conditions of the system : closure / opening , interface behaviour, etc.

21. THM interaction in the near field s , e s , e From Gens, 2003 Desaturation ? Saturation rate, duration, etc.

22. Unsaturated THM behaviour investigation • URLs : THM behaviour in a realistic geological conditions • RESEAL, BACCHUS , etc. ( HADES) • Prototype test at Aspo • Febex test at Crimsel • etc. • Laboratory tests (small scale + mock-up) • Small scale : Identification and study of the individual process by carefully controlled lab test conditions • Suction , Temperature , Stress paths controlled • Microstructure study • etc; • Mock-up : coupled processes at large scale & well controlled boundary conditions • Numerical modelling : Analysis and predictions of the repository performance • Formulations : based on sound physical principles • Formulations / codes: take into account all relevant phenomena + interaction • Validated by lab and in situ tests

23. Lab tests : Odometer cell with suction controlVapour equilibrium technique thermometers vapour lines thermostats oedometer cell temperature controlled vessel with saline solution

24. Numerical codes development • Code – Bright ( UPC ) • Lagamine code ( Ulg ) • Compass code ( Cardiff ) • etc. Validation in Catsius clay project : unsaturated clay THM processes BMs for numerical codes

25. Example : Ophélie mock-up heating cables Lay-out On-surface Preliminary Heating simulation Experimenting Later Instruments and Equipment Large scale THM behaviour of the buffer material

26. Example : Ophélie mock-up Experiment evolution • hydration at ambient temperature : flooding 3 bar, then stepwise to 10 bar • heating (with external temperature) : • central : 450 w/m, • external : 95 – 120 °C • cooling • dismantling and analyses

27. Example : Ophélie mock-up Swelling pressure in the Mock-up Questions : swelling pressure << designed value (4.5 MPa) ? swelling pressure decreasing : collapse ? instrumentation artefact ? Sw effect ?

28. Example : Ophélie mock-up Lab THM characterisation program • Fundamental T-H-M properties determination • thermal conductivity • hydraulic conductivity at different sw (or s), T states • water retention property (srw /w - s ) • swelling pressure • Lab mechanical tests • (unsaturated constitutive law building/parameters determination) • s and T controlled odometer tests : • wetting - drying paths at different loads and T • loading - unloading paths at different s and T • s and T controlled triaxial tests

29. Fundamental T-H-M properties Unsaturated permeability Water Retention

30. Fundamental T-H-M properties • Swelling pressure • depends mainly on the dry density • T seems to decrease the swelling pressure

31. Odometer test results. Loading-unloading cycles at  = const. 1 7 7 8 c 1 7 5 9 c 1 7 7 4 c 1 7 5 6 c 1 7 7 7 c 1 7 7 2 c 0 s t a r t i n g y = 3 M P a p o i n t ) % 2 ( v e , 4 n i a r t s 6 60MPa c i r t e 8 m u Yielding ! l 40MPa o V 10 o 2 2 C o 8 0 C 3 MPa 12 0.01 0.1 1 10 s V e r t i c a l n e t s t r e s s , ( - u ) M P a v a stiffness against loading increases with suction ! Low yielding value ! T seems to enhance the phenomena

32. Odometer test results. Drying- Wetting cycles Stiffness against suction highly dependent of stress applied !

33. Swelling/collapse upon wetting Zone of potential collapse Oed. Tests : wetting phase Parameters for modelling !

34. Parameters for mechanical constitutive law BBM law

35. Numerical simulation with Lagamine code Swelling pressure decreasing : collapse + T effect

36. An example of the interaction seal/BC Shaft seal hydration (Reseal project) 2000 L of water artificially injected = 50% of expected volume 2 years after hydration >75% of RH reached after 2 y of hydration, full saturation not reached after 5y

37. An example of the interaction seal/BC Shaft seal:EDZ evolution in host rock (Reseal project) Time needed for pressure increase depends on hydration of seal Pressure increase from Furthest to nearest filter

38. An example of the interaction backfill/BCBACCHUS 2 (Catsius clay project) 3 m Importance of the interface behaviour !

39. Conclusions / Discussion • Unsaturated THM processes are limited in the near field, mainly concern the ECs and immediate adjacent host rock • Unsaturated THM behaviour of BC needs more investigation (phDs) • THM transient : probably not critical issue for LT safety But important to support SC • Unsaturated THM coupling processes (high/weak) depend highly on the hydraulically conditions , therefore need to be studied and considered for the design of the repository • Spacing of the canisters, galleries, etc. ? • Sequence of the canisters emplacement ? • Sequence of the closure/sealing of the galleries ? • Ventilation control ? • Etc.

40. Thank you very much !