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.

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).