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

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 the disposal facility is strongly linked to the durability of these engineered barriers and 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 not yet very well characterised and need to be appropriately addressed in safety assessments.

The SUDOKU approach is to combine the investigations on multilayer covers with the durability of cementitious barriers to assess the transfer properties of mobile radionuclides in damaged cementitious barriers according to their chemo-mechanical evolution.

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

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

This Work Package aims to understand 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.