Mock-up OPHELIE - Dismantling

1. Mock-up OPHELIE - Dismantling Jan Verstricht Exchange meeting n° 2 31 May 2001

2. Outline • Current status of the mock-up experiment • Preparation of the dismantling • Dismantling objectives • Post-dismantling investigations • Scenario and implementation • Conclusion

3. 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

4. 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

5. Instrumentation of the mock-up

6. Concrete segment ring and temperature control system heating cables load cells pressure cell

7. Different phases of the mock-up • hydration at ambient temperature • heating (with external temperature control) • cooling • dismantling and analyses

8. Evolution of hydration (volume injected)

9. Temperature evolution

10. Backfill pressure sensors (Kulite)

11. 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

12. 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)

13. 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)

14. 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

15. 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)

16. 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

17. 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”)

18. Location of the backfill samples

19. Temperature profile

20. Water content and density distribution

21. 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?

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. Global planning of the dismantling

30. 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