"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009 1 Impact of TMHC-processes on the safety of...
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Transcript of "Salt" Working Group TIMODAZ - THERESA Luxembourg_2009 1 Impact of TMHC-processes on the safety of...
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
1
Impact of TMHC-processes on the safetyof underground radioactive waste repositories
Salt Working Group
Chair: Tilmann Rothfuchs, GRSRapporteur: Otto Schulze, BGR
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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"Salt" Working Group: Main Topics & Results
1. TMHC - Processes
Knowledge and understanding of relevant processes → constitutive models
► TM: material behaviour in the far-field
► TMHC: processes in the near-field and evolution of repository system including evolution of barriers (outer natural barrier, host rock and engineered
barriers)
DRZ evolution (convergence, damage, …) and interfaces (rock - backfill)
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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"Salt" Working Group: Main Topics & Results
1. TMHC - Processes
Knowledge and understanding of relevant processes → constitutive models
► TM: material behaviour in the far-field
► TMHC: processes in the near-field and evolution of repository system including evolution of barriers (outer natural barrier, host rock and engineered
barriers)
DRZ evolution (convergence, damage, …) and interfaces (rock - backfill)
2. The requirements for the "Complete Containment"
and how to achieve the respective safety proof
► complete containment (FEP - if ... then)
► requirements concerning (TS)PA & LTSA (safety case) - tool box complete ?
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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1. TMHC - Processes & Models
► relevant processes: TM-far field … TMH(C)-near field
► constitutive modeling (recent developments: Saltmech_6, 2007)
TM-far field: (thermo-mechanical impact - in general: excavation & heat)
transient creep (including recovery of strain hardening),
steady-state creep (reliable long-term extrapolation),
dilatancy boundary and propagation of damage (EDZ), (◄ Luxembourg 2003)
softening and failure,
post-failure strength (residual strength),
… humidity induced processes (impact on strength and ductility)
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Requirement for modelling the near-field processes ► FEP catalogue
- thermal and mechanical impact > stress & stress redistribution
- deformation (viscous creep; dilatancy: damage … softening & failure)
- impact of fluid pressure on state of stresses (M-H coupling)
- impact of moisture on … (M-C coupling)
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Requirement for modelling the near-field processes ► FEP catalogue
- thermal and mechanical impact > stress & stress redistribution
- deformation (viscous creep; dilatancy: damage … softening & failure)
- impact of fluid pressure on state of stresses (M-H coupling)
- impact of moisture on … (M-C coupling)
Of special importance …
- EDZ evolution (micro-fracturing and pathway generation)
- EDZ devolution (convergence and re-compaction)
(normal and altered evolution scenario)
Special emphasis on permeability evolution / devolution
… regarding complete containment
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Repository System; Release Scenario
D. Buhmann
Access Path to Near Field
Waste ContainerMobilisation
Near Field
Geosphere; GroundwaterBiosphere
= Flow of Contaminated Water
Keep the limits !!
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Overburden
Host Rock Isolating Rock Zone
Repository
Water bearing strata
Change of philosophy: From release scenario to complete containment
repository
Isolating Rock Zone (IRZ)
Boundary of IRZ Red line? Black line?
What affects the IRZ? drifts crossing IRZ > technical
barriers faults or water-bearing layers in
the geological environment crossing IRZ
IRZ must be chosen before license application
Workshop TIMODAZ Luxembourg, D. Buhmann, Sept. 30, 2009 10
= technical barrier
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Proof of "Complete Containment": Process understanding > Constituve models > Tool box
• development of constitutive models allowing reliable long-term prediction (THERESA project)
• model implementation in process level codes for the PA
(LTSA - long-term safety analysis)
• implementation of simplified models for TSPA (total system performance assessment)
important challenges: • key scenarios: which FEPs may strongly affect the near-field integrity?• DRZ evolution with respect to damage and re-compaction? • Predictive capabilities of modeling and integration in PA level-models and
into tools for the safety case?
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Workshop discussion result (1): Need for improvement and refinement of models
• permeability relation(s): what is affecting permeability?
- k = f(Φ, σmin); Φ ≡ εvol (e.g. Stormont, Müller-Lyda, Popp, Heemann, …)
- k = f(σmax/ σeff) (e.g. Peach, Alkan, ...)
- others: loading geometry, crack orientation, connectivity, aperture, …
• evolution / devolution of porosity > physical understanding of healing/sealing is variable (dry vs. wet)
• mechanical / hydraulic coupling: determination of Biot‘s parameter ασeff = σmin - α ∙ pfluid
• prerequisite: additional experiments especially tuned to identified requirements
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Workshop discussion result (2): Need for improvement and refinement of models
• Physical-Chemical Processes After Brine Inflow (worst case scenario)
- Gas Generation and Migration (EBS - IRZ)
- Gas entry pressure / Infiltration in and out of Salt Barriers (IRZ)
- Two-phase flow in rock salt ??
• Criterion(s) for Proof of Integrity of the Barrier System (e.g. IRZ)
► Increase of fluid pressure, driven by convergence / gas production
- Dilatancy Criterion
- Minimum Principal Stress Criterion (hydraulic criterion)
• backfill material (e.g. crushed salt) in the engineered barrier system
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Crushed salt / granular salt backfill:
Reconsolidation of granular salt at ambient temperature is quite well (i.e.
quantitatively) understood ► technical demonstration in lab and field tests.
Micro-mechanics for ambient re-consolidation as well as for fluid assisted
pressure-solution and redeposition are documented.
Technical proof for re-consolidation at elevated temperature (HLW ≤ 200 °C)
and sound understanding of micro-mechanics is not available.
HLW-repository operation in a salt formation requires a sound process
understanding with respect to:
- the mechanisms of re-consolidation of granular salt backfill
- the determination of a permeability-porosity and its evolution
"Salt" Working Group TIMODAZ - THERESA Luxembourg_2009
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Summary: ... why further improvements - just for fun?
Improvement of process understanding and refinement of models:
Confidence building and reduction of uncertainties
- needed for reliable long term safety assessment
(extrapolation on long-term scale; safe predictions)
- in general, only short-term experiences available from lab and in situ testing
also needed:
sensitivity studies to cover uncertainties, e. g. facies, mineral composition, ...
./.