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Mock-up OPHELIE - Dismantling. Jan Verstricht Exchange meeting n° 2 31 May 2001. Outline. Current status of the mock-up experiment Preparation of the dismantling Dismantling objectives Post-dismantling investigations Scenario and implementation Conclusion.

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mock up ophelie dismantling

Mock-up OPHELIE - Dismantling

Jan Verstricht

Exchange meeting n° 2 31 May 2001

outline
Outline
  • Current status of the mock-up experiment
  • Preparation of the dismantling
  • Dismantling objectives
  • Post-dismantling investigations
  • Scenario and implementation
  • Conclusion
current status of the mock up
Current status of the mock-up
  • Overview of the set-up
  • Hydration and heating history
  • Main measurement results
    • temperature evolution
    • pressure evolution
  • Other observations
    • chemical phenomena
experimental set up mechanical details
Experimental set-up: mechanical details

55 mm thick + 3 mm lining

hydration tube

(x 16)

welded cover

main cover

flexible joint

feed-through (2x) for

instrumentation cables

25 mm thick

Ø 2000 mm

Ø 458 mm

disposal tube with heating elements

4785 mm

concrete segment ring and temperature control system
Concrete segment ring and temperature control system

heating cables

load cells

pressure cell

different phases of the mock up
Different phases of the mock-up
  • hydration at ambient temperature
  • heating (with external temperature control)
  • cooling
  • dismantling and analyses
overview of observations
Overview of observations
  • Higher than expected (apparent) thermal conductivity
  • Low swelling pressures
  • Pitting corrosion detected on stainless steel tubing
  • Sensor failure
  • Water samples show high content of Cl-
      • most probably from the backfill itself
  • Presence of free sulphides in the mock-up water
evidence of geochemical phenomena
Evidence of geochemical phenomena
  • Mass transport process within the backfill material
    • advective transport of soluble salts by a water front
    • migration through an unsaturated material
    • advection/evaporation cycles (heat pipes)
    • thermo-osmosis, thermo-diffusion
  • Presence of free sulphides
    • residual pyrite
    • sulphate reducing mechanism (thermal or microbial)
preparation of the dismantling
Preparation of the dismantling
  • working group (EURIDICE, SCK•CEN, N/O):
    • definition of objectives
    • overview of analyses and investigations
    • sampling programme
    • dismantling scenario
    • technical and logistical support
      • dismantling and sampling techniques
      • quality assurance
      • safety
  • input from DAC (May 10), SAC with Int’l experts (25 June)
dismantling objectives and applications
Dismantling objectives and applications
  • better understanding of the backfill behaviour
    • main phenomena (THM, physico-chemical, microbiological) occurring in backfill during the experiment
    • consequences on integrity and performance of the mock-up components
    • performance of metallic components (corrosion susceptibility) and concrete segments in HLW disposal conditions
  • scientific and technical optimisation of the PRACLAY in situ experiment
    • components, installation
    • monitoring (what to monitor, which sensors)
  • input for current review of HLW disposal concept
analyses and investigations 1 3
Analyses and investigations (1/3)
  • hydration process: saturation degree?
    • density and water content distribution
    • permeability tests
  • thermal characteristics ® conductivity
    • other heat transfer mechanisms (mass transport)
  • occurrence of corrosion
    • analysis of main metallic components in contact with backfill
    • incl. physico-chemical and microbiological characterisation
      • porewater chemistry (squeezing or leaching)
      • microbiological analyses (Sulphato-Reducing Bacteria)
analyses and investigations 2 3
Analyses and investigations (2/3)
  • HM properties of backfill material
    • swelling, retention curve
  • performance of central tube
    • rechecking tube dimensions (plastic deformation)
    • quality of welding (related to corrosion)
  • sensor performance
    • recalibration to correct measurement data
    • failure mode where applicable
analyses and investigations 3 3
Analyses and investigations (3/3)

Additional opportunities of dismantling

  • Behaviour of joints between backfill blocks
    • physico-chemical and hydraulic behaviour
  • Geomechanical properties of backfill
    • E, n, Mohr-Coulomb
  • Concrete characterisation
    • mechanical behaviour
      • compression and tension, flexion, shear strength
      • ultrasonic auscultation
    • porosity, water content, water infiltration depth
  • Concrete - backfill (clay) interface (“alcaline plume”)
general remarks
General remarks
  • sampling operations
    • no sampling at elevated temperature/pressure
      • backfill characterisation after heated phase (« at elevated temperature)
    • sampling has to be representative for the mock-up state
      • porewater chemistry:best practices (leaching, squeezing)
  • backfill characterisation
    • understanding of main processes
      • requires knowledge of boundary conditions (Eh, pH,…), even if these are not representative for in situ conditions
    • is backfill able to fulfil its requirements?
dismantling scenario
Dismantling Scenario
  • phase 1: final preparation before heater switching off
    • final check of all equipment and work procedures
    • water sampling for geochemical characterisation
      • porewater composition
      • dissolved gas (may indicate chemical or microbiological processes)
      • Eh-pH measurements
    • sensor status check
dismantling scenario23
Dismantling Scenario
  • phase 2: cooling phase
    • central tube: general position (survey), internal dimensions
    • rapid cooling to preserve state (2 to 4 weeks)
      • complete switch-off, with removal of thermal isolation
      • external water pressure cut-off when Tmax < 100 °C
        • rapid pressure drop
    • penetration test through one of the instrumentation covers

when mock-up is not more than 5 °C warmer than demohall

    • radial profile sampling of backfill
      • drilling through jacket
      • pressure
    • water sampling
dismantling scenario24
Dismantling Scenario
  • phase 3: instrumentation
    • sensor status, re-organising of data-acquisition
      • selected sensors will be read-out during dismantling
    • purging hydration circuit
    • removal instrumentation covers
dismantling scenario25
Dismantling Scenario
  • phase 4: removal of main cover and sampling/removal of backfill
    • dismantling / sampling operations
    • conditions: 24h/24h, 7/7 days
    • retrieval of central tube
    • sampling of metallic components
    • cleaning operations
dismantling sampling operations method 1 2
Dismantling/sampling operationsMethod (1/2)
  • Continuous visual inspection of backfill, sensors and metallic structure during dismantling
    • special features, e.g. anomalous consistency/colour

cavities (water filled)

joints between blocks

corrosion

    • additional samples may be taken
  • optical survey to record systematically the location of all samples and sensors
dismantling sampling operations method 2 2
Dismantling/sampling operationsMethod (2/2)
  • Documentation
    • video shots of all main operations
    • dismantling logbook
    • sampling sections
    • sample track records
  • Dismantling crew of seven persons
    • sampling/dismantling: 2 + 1
    • sample packaging (labelling, storage): 2 + 1
    • general co-ordination: 1
  • All equipment, work procedures, and operations under supervision of safety manager
logistic support
Logistic support
  • removal and sampling of backfill material
    • behaviour of backfill material?
    • homogeneity
  • Quality Assurance (procedures, forms,…): traceability
    • recording of all dismantling/sampling and pre-/post-dismantling operations
    • sample track record for each sample (backfill core, sensor,…)
    • operations according to procedures/instructions
      • flexibility for non-conformities, with registration

®QA to reduce risk of errors, which could lead to loss of data, wrong interpretation of results

conclusion and perspectives
Conclusion and perspectives
  • Dismantling objectives
    • defined by large participant base
  • Specification of analyses and tests
  • Detailed work plan
    • minimal time span for dismantling activities
    • quality assurance for maximum reliability of results
  • Final review of all measurement data, observations, and analysis and test results with our main partners

® final conclusion of mock-up experiment

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