"Salt" Working Group TIMODAZ - THERESA Luxembourg_ Impact of TMHC-processes on the safety of underground radioactive waste repositories Salt Working Group Chair: Tilmann Rothfuchs, GRS Rapporteur: Otto Schulze, BGR

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ "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_ "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 4

5 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_ 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_ 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_ Repository System; Release Scenario D. Buhmann Access Path to Near Field Waste Container Mobilisation Near Field Geosphere; Groundwater Biosphere = Flow of Contaminated Water Keep the limits !!

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ 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, = technical barrier

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ 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_ Workshop discussion result (1): Need for improvement and refinement of models permeability relation(s): what is affecting permeability? -k = f(Φ, σ min ); Φ ≡ ε vol (e.g. Stormont, Müller-Lyda, Popp, Heemann, …) -k = f(σ max / σ eff ) (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 α σ eff = σ min - α ∙ p fluid prerequisite: additional experiments especially tuned to identified requirements

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ 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_ 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_ 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,..../.

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ Improvements since the EDZ workshop 2003, remaining uncertainties 16  A project on model development for gas permeation showed that gas entry at pressures slightly above minimum principal stress leads to dilatancy-controlled gas flow rather than gas-frac, and at least partial self-sealing was confirmed (Popp & Minkley, 2007).  The German cooperation project “Development of constitutive laws” yielded improved material laws that entered in THERESA: A variety of constitutive laws for describing dilatancy, dilatancy-induced permeability increase, and self-sealing were further developed and validated by different modelling teams.

"Salt" Working Group TIMODAZ - THERESA Luxembourg_ Host rock (far field)  Recent developments in constitutive laws, (THM(C)-near field … (TM-far field))  Criteria of integrity assessment  Gas generation and consequences: permeation and migration affecting isolation and transport properties of the host rock EDZ (near field): Improvements since the EDZ workshop 2004, remaining uncertainties  Damage evolution … affecting strength and integrity  Healing/self-sealing/recompaction  Porosity-permeability relation  Mechanical hydraulic coupling, models and parameters Backfill (crushed salt)  Compaction  Porosity-permeability relation  Mechanical hydraulic coupling, models and parameters  Impact of brine  Importance of C-coupling … with respect to waste products and a candidate buffer material Remaining Research Needs of the Salt Option

The REPOPERM-project 18 Key question from the viewpoint of „complete containment“  What are the hydraulic properties of compacted crushed salt at the end of compaction?”  What is the lower limit of backfill porosity/permeability which is critical or uncritical, respectively with regard to a possible water inflow into a HLW repository or a violation of the complete containment Situation at start of the project  Porosity measurements in the range of 1-3% and below are severely questionable Project objectives  To avoid unnecessary intricate and costly laboratory measurements the relevance of crushed salt properties below 1-3% will be checked first by sensitivity analysis’ based on model calculations