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Geochemical oriented in situ experiments Geert Volckaert

Geochemical oriented in situ experiments Geert Volckaert. Overview. Clay geochemistry Pore water sampling and in situ measurements of pH and Eh Projects: e.g. ARCHIMEDE, ORPHEUS, MORPHEUS Radionuclide and gas migration In situ RN diffusion experiments, gas injection experiments

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Geochemical oriented in situ experiments Geert Volckaert

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  1. Geochemical oriented in situ experiments Geert Volckaert

  2. Overview • Clay geochemistry • Pore water sampling and in situ measurements of pH and Eh • Projects: e.g. ARCHIMEDE, ORPHEUS, MORPHEUS • Radionuclide and gas migration • In situ RN diffusion experiments, gas injection experiments • Projects: e.g. CP1, TRANCOM, MEGAS • Geochemical perturbations • Influence of heat and radiation • Project: e.g. CERBERUS

  3. Line out Line in Filtermaterial Basic design of piezometers Multi-filter assembly

  4. Mobile OM characterisation MORPHEUS piezometer • TOC evolution • In time • Related to physical or chemical disturbances • Spatial heterogeneity • Comparison with immobile OM at same level

  5. ORPHEUS: testing different non-metalic filter materials for pH, Eh

  6. POROUS PLATE WATER TUBING 10 CM SOURCE 3 - 9 M CLAY CORE MIGRATION TEST (with radioactive sources) IN-SITU MIGRATION PERCOLATION EXPERIMENT In situ radionuclide migration test for sorbing radionuclides

  7. In situ Cs migration experiment

  8. HTO Design of CP1 HTO injection test

  9. CP1: HTO migration

  10. Test Drift Horizontal Ring 41 9 7 6 5 4 3 2 1 Injection filter #8 1 2 3 Vertical 4 5 6 7 Injection filter #8 9 TRANCOM: testing anisotropy in migration of organic matter labelled with C-14

  11. MEGAS: in situ gas injection test

  12. MEGAS: in situ tracer test after gas injection

  13. CERBERUS PROJECT CERBERUS: the dog with 3 heads who guards the underworld HADES

  14. Objective of the project • To simulate the disposal in Boom Clay • of a vitrified HLW COGEMA container after 50 y cooling time • in a “borehole” type repository design • without overpack • includes simulation of both heat output and g-irradiation field

  15. Studied phenomena and processes Thermal response Hydro-mechanical response of Boom Clay on heating Radiolysis in Boom Clay (H2 formation) Combined effect of heat and radiation on Boom clay mineralogy and geochemistry Migration of redox sensitive elements Corrosion of overpack materials and waste matrixes Backfill material properties (Boom Clay) Including modelling of T, TH, THC and R

  16. Design

  17. Lower part of CERBERUS Heater Filter

  18. Experimental history • 1987-1989: Design, safety report and construction • 1990-1994: installation and HLW simulation by heat and radiation • 1995 : Cooling phase • Survey and modelling of NF effects • Analysis migration experiment with Am/Tc • 1996-1998 : Analysis of the Near Field effects • Hydration of the Cerberus backfill • Thermo-hydro-geochemical modelling • Characterization of the Cerberus NF • Feedback to Performance assessment

  19. Monitoring • Temperature: thermocouples => very reliable • Pore water pressure: piezometers => very reliable • Radiation dose: classical dosimeters => very reliable • Total stress: piezo-electric sensors => survived less than 1 month irradiation • Hydrogen: by adsorption on Pd wire => very sensitive • Chemical parameters by sampling

  20. Hydro-chemistry • conditions: up to 100 °C and up to 13 MGy during 5 years; • water chemistry: Na-HCO3 Na-SO4 Na-HCO3 • pH decreases from 8.5 to 7.3; • Eh remains reducing: ~ -273 mV (SHE 25 °C); • presence of thiosulphate (2 E-04 M) and oxalate (4 E-04M)

  21. Boom Clay mineralogy • conditions: up to 100 °C and up to 13 MGy during 5 years; • no illitisation of smectite; • pyrite oxydation producing gypsum around framboids, but; • maintains its “self-healing” properties

  22. Migration

  23. Matrix materials • Experimental conditions: • 5 years at 85 °C and 115 Gy/h (total dose: 5 MGy) • Glass samples: SON68, SM513R, SM527, WG124 • visual observations • weight loss : Cerberus 20 % to 50 % < Corrosion loops • secondary phases : compounds with sulphur • Concrete samples: CAC; gallery • CAC: no detectable chemical change • amorphous C-S-H phase • concrete gallery: reaction zone of 0.8 mm rich in Fe

  24. Corrosion • Experimental conditions: 5 years at 85 °C and 115 Gy/h (total dose: 5 MGy) • AISI309, C steel, Cu, Hasteloy C4, Nirosta, Ti/Pd and TMI115 ~ no corrosion • Cerberus ~ Corrosion loops, excepted for welded C steel and Cu • welded C steel: • corrosion rate is up to 8 x usual values • pitting and intergranular corrosion • Cu • pitting corrosion

  25. Corrosion

  26. Concluding remarks • Broad experience in the design, installation and operation of in situ geochemical set-ups is available • These set-up are very versatile and can be easily adapted to various objectives and conditions • The set-ups work reliably over many years (up to more than 15 years!)

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