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The Unsaturated THM behaviour in porous material - an important issue for a HLW repository Li X.L. EIG EURIDICE Exchange - Meeting 6 June 2006
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 ?
Saturated porous media • Two phases porous media : • Solid • water ( dissolved gas) uw > 0, Srw = 100 %
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 %
Unsaturated porous media ! Matrix suction : If saline water : Total suction = matrix suction + osmotic suction
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 !
Thermal processes : Heat transfer convection Conduction vaporisation G = f (s,n, T )=>(H-T, M-T) Couplings : Convection => H -T Vaporisation – condensation => TH
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 !
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
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
Mechanical processes : suction effects Volumetric Deviatoric Shear strength increases Stiffness increases Hardeing,
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 ,
Mechanical processes : Temperature effects DT dilation DT reversible e T-e f (s)
Mechanical processes : Temperature effects T softening
Mechanical processes : Constitutive law BBM model + T effects : elasticity, softening, etc.
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 !
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
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 !
Scheme of THM processes in the near field s , e s , e From Gens, 2003
Coupled phenomena in vapour transport Coupling ( strong/weak) depends on the boundary conditions of the system : closure / opening , interface behaviour, etc.
THM interaction in the near field s , e s , e From Gens, 2003 Desaturation ? Saturation rate, duration, etc.
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
Lab tests : Odometer cell with suction controlVapour equilibrium technique thermometers vapour lines thermostats oedometer cell temperature controlled vessel with saline solution
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
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
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
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 ?
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
Fundamental T-H-M properties Unsaturated permeability Water Retention
Fundamental T-H-M properties • Swelling pressure • depends mainly on the dry density • T seems to decrease the swelling pressure
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
Odometer test results. Drying- Wetting cycles Stiffness against suction highly dependent of stress applied !
Swelling/collapse upon wetting Zone of potential collapse Oed. Tests : wetting phase Parameters for modelling !
Numerical simulation with Lagamine code Swelling pressure decreasing : collapse + T effect
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
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
An example of the interaction backfill/BCBACCHUS 2 (Catsius clay project) 3 m Importance of the interface behaviour !
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.