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The PRACLAY experiment

The PRACLAY experiment focuses on enhancing the understanding of deep geological disposal systems for radioactive waste. Recent revisions to its objectives emphasize methodical study of system components, including the hydration processes, thermal loads, and interactions within the disposal environment. The experiment aims to verify existing theoretical models through in-situ observations, offering insights into the behavior of materials under realistic conditions. Key outputs include the characterization of disturbed zones, hydration verification, and understanding geochemical processes, with proposals for additional experiments to further investigate corrosion and migration phenomena.

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The PRACLAY experiment

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  1. The PRACLAY experiment Exchange meeting n°1: EIG PRACLAY - SCK•CEN - ONDRAF/NIRAS 18/01/01

  2. The objectives of the PRACLAY experiment have been revised • Revision of the objectives (April 2000) • Report ‘Methodical and detailed description of the PRACLAYExperiment’ • Revision of the design • longitudinal design (plugs, central tube, ...) • hydration system • thermal load • instrumentation • proposal of additional experiments

  3. The PRACLAY experiment • in-situ verification and confirmation of the present status of scientific and conceptual knowledge; • better understanding of • the disposal system; • the interactions between its different components.

  4. Differences exist with the real disposal concept • Geometry • Influence of the boundary conditions • Thermal load • Hydration process • Instrumentation • The PRACLAY experiment will not reflect exactly the real concept but will give the tools to understand it with a good confidence level

  5. Instrumentation is installed to observe the behaviour of the different components • Instrumentation has to be optimised so that as much meaningful information as possible can be collected from each sensor; • Instrumentation has to be redundant to guarantee that a sufficient fraction will resist at long term; • External devices (instruments, samples, ...) may never alter the demonstration character of the PRACLAY experiment.

  6. Confirm and improve our knowledge of the reference concept • Comparison between • Prediction based on our interpretation of the reality (models) • What we can measure • Agreement=> a certain prediction level is reached=> confirmation of our knowledge • Difference=> some aspects are misunderstood=> improvements are required

  7. The desired output is (1): • Observation of the behaviour of the whole disposal system: • interactions with the main gallery • plugs • central tube (possibility of retrievability) • Characterisation of the disturbed zone (EDZ and TDZ) and its evolution in time • verification of the hypothesis considered in the performance assessment

  8. The desired output is (2): • Verify the hydration process through the backfill material • useful information for the work sequence of the final repository • Study of the THM phenomena occurring inside the backfill material and the possible Geochemical coupling • heat and water transport process • swelling capacity of the backfill

  9. The desired output is (3): • The study of the Geo-Chemistry phenomena • Microbial characterisation • Saline fronts • concentration of chloride • problems of pitting corrosion • Alkaline plume • decrease of the swelling properties • hardening by precipitation of calcium carbonate • Oxydation of Boom clay • Thermal degradation

  10. Additional experiment proposals • Corrosion - Bruno Kursten • Migration - Pierre De Cannière

  11. Localised corrosion of candidate overpack materials on a 1:1 scale • Ring shaped elements • around the central tube - isolated electrically • makes part of the central tube (welding) • Contact with bentonite - Mock-up 1000mg/L Cl- • Characterisation of the chemical composition of the backfill pore-water (anion content, pH, temp., oxygen content, …) • Determination of the corrosion potential Ecorr under realistic conditions

  12. Migration experiment (1) • Radial piezometers outside the middle of the PRACLAY experiment • Aim: • general characterization of the transport properties of the backfill at large scale and under in situ conditions; • models validation; • detection of preferential water paths in the backfill.

  13. Migration experiment (2) • Migration experiment on backfill and Boom Clay samples after a thermal loading (in lab) • In situ migration experiments in Boom Clay after dismantling of the PRACLAY experiment

  14. Current choices forthe PRACLAY experiment • Thermal load: ~240 W/m • 100 °C after 5 years of heating • 30 °C after 1 year of cooling • Lining designed to resist to the mechanical and the thermal load • Backfill material: the same as form OPHELIE • Swelling pressure limit to 2 MPa • Radial hydration from outer

  15. The longitudinal design of the PRACLAY experiment

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