Near-surface disposal optimisation based on knowledge and understanding (SUDOKU)

Objectives

Understanding the behaviour and performances of (i) covers and (ii)cementitious barriers of near-surface disposal facilities for short lived waste (ground level facilities) and ILW (shallow deep facilities) in view of these barriers optimization to ensure the long-term safety of disposal facilities.

Major highlights (October 2024 - March 2025) 

• Developing the content of the initial SOTA report and establishing the main contributors to writing the SOTA report.
• Designing the on-site experiments and the monitoring system, and defining the different conditions to be reproduced. Starting to prepare the complementary laboratory scale experiments.
• Completion of Milestone MS 14 outlining the protocols to be used by Taks 4 partners to obtain degraded mortar/concrete samples considering different degradation processes such as carbonation, leaching with different solutions relevant to the national context of the near-surface disposal facilities and mechanical constraints. The Milestone report also includes a description of the characterization methods and different experimental setups for diffusion tests.

Forward look

• Finalizing the first draft of SOTA report
• Compile all the necessary materials, spaces, and instrumentation to start running the first tests and sensor’s calibration for the laboratory experiments related to the multilayer cover; 
• Start the degradation tests for mortar/concrete samples to be used both to assess the effect of chemical and mechanical degradation and for the radionuclide diffusion tests

Description of the WP

The safety of surface disposal facilities typically relies on the performances of the multilayer cover and cementitious barrier system, as the main contributor to the dose are the long-lived mobile radionuclides which mobility through the disposal zone depends closely on the properties of these engineered barriers. The water flux passing through thedisposal facility is strongly linked to the durability of these engineered barriersand influences the migration of mobile radionuclides (³⁶Cl, ¹⁴C, ⁹⁹Tc,¹²⁹I....). The impacts of cracks and steel corrosion products on radionuclide transfer in cementitious barriers are notyet very well characterised and need to be appropriately addressed in safetyassessments.

The SUDOKU approach is to combine the investigations on multilayercovers with the durability of cementitious barriers to assess the transferproperties of mobile radionuclides in damagedcementitious barriers according to their chemo-mechanical evolution.

The novelty of SUDOKU consists of (i) the analysis of the evolution of hydraulic properties of themultilayer cover with laboratory and on-site experiments, (ii) experimental and modelling data aboutdegradation of reinforced and unreinforced cement-based materials in near surfacedisposal conditions, and (iii) transport properties of mobile radionuclides in degraded and corroded reinforced cement-based materials.

SUDOKU will provide understanding of the long-term integrityand performance of the multilayer cover under different meteorological conditionscontributing to the optimization of this important barrier.The improved characterization of the durability and performance of the EBS, achieved by the work proposed inSUDOKU, will reduce the uncertainties, and improve the Safety Assessment (SA). The use ofproven models in combination with on-site and laboratory studies will ensurethe necessary reliability of the results and facilitate the determination of the optimalEBS configuration from the safety point of view.

Outcomes

• Understanding of the factors controlling different combinations of layers in the multilayer cover structure (water and energy flows, erosion, …) and the long-term performances of the cover (Innovation for optimisation);
• To improve the understanding of the cementitious barriers degradation and its effect on the transfer properties of mobile radionuclides (Scientific insight and implementation safety);
• Recommendations for future optimizations of repository designs to improve the repository safety (Implementation safety).