SUDOKU „Near-Surface Disposal Optimization Based on Knowledge and Understanding“ is one of the WPs cofinanced by the European Union under the European Partnership on Radioactive Waste Management (EURAD-2). 

Under RATEN leading, SUDOKU is bringing together specialists from 29 European institutions to jointly perform laboratory experiments and in situ tests, combined with modelling studies, with the aim of deepening the current understanding of the behaviour and performances of multilayer covers and cementitious barriers of near-surface disposal facilities.  The activities started on October 1st, 2024.

The combined effects of the performance over time of multilayer covers and the chemo-mechanical evolution of the cementitious barriers on the transport properties of mobile radionuclides will be evaluated and recommendations for optimizing these barriers from the safety point of view will be developed.

The work proposed to be performed under SUDOKU is organized in three technical tasks dedicated to (i) the performance of multilayer covers (Task 3), (ii) the chemo-mechanical evolution of reinforced and unreinforced cementitious barriers and the effect on the migration of mobile radionuclides (Task 4), and (iii) modelling the evolution of the engineered barrier system (EBS) and its effect on radionuclide migration based of the experimental results obtained in SUDOKU (Task 5). These tasks are complemented by a task dedicated to knowledge management (Task 2) aiming to capture knowledge relevant for SUDOKU and to contribute, through the EURAD-2 KM programme, to knowledge transfer to the EURAD-2 community and beyond.

In situ monitoring on existing multilayer cover mock-ups and modelling will be performed to improve the current state of knowledge of the processes that control water infiltration in multilayer covers and to evaluate the cover effectiveness and its long-term performance. The behaviour of different soil layers and combinations of layers that form the cover will be studied by in-situ monitoring as well as laboratory scale experiments to guarantee controlled conditions.

Furthermore, the coupling of mechanical constraints and chemical alterations on unreinforced cement-based materials and similar systems with steel reinforcement, as well as the coupled effect on mobile radionuclide migration will be investigated through laboratory scale experiments. This will allow to assess the consequences of the cementitious EBS chemo-mechanical degradation on mobile long-lived radionuclides migration under relevant conditions for near-surface disposal facilities.   

The experimental results achieved under SUDOKU Task 3 & 4 will be integrated in the modelling performed in Task 5 to assess the mechanical and chemical consequences of corrosion of steel reinforcement and degradation of EBS materials on the transport of the radionuclides with negligible sorption in geosphere (e.g. C-14, Cl-36, I-129, Tc-99) whose release from the disposal area may be affected by the EBS evolution. 

The combination of on-site and laboratory studies with state-of-the-art numerical models will ensure the necessary reliability of the results and facilitate the elaboration of recommendations for optimal EBS design  from the safety point of view.

SUDOKU is strongly linked with different national projects (i.e. Spanish project on multilayer cover, Belgian, Bulgarian, Czech, French, Romanian and Slovenian surface disposal programmes) and effective interactions of mutual interest with other EURAD-2 WPs (CLIMATE, OPTI, RAMPEC, HERMES, OPTI) are going to be established.

In the frame of SUDOKU Task 4, RATEN ICN performs an experimental programme to assess the degradation of cementitious barriers of the future Romanian near-surface repository (DFDSMA) and the effect of cement based barriers degradation on the mobility of the main long-lived radionuclides that are present in the inventory of the waste intended to be disposed of in this facility (C-14, I-129 and Tc-99). The co-financing of this experimental program is ensured through dedicated RATEN R&D programme on radioactive waste management that is financed by the Romanian Ministry of Energy. As member of End User Group of SUDOKU, the Romanian waste management organization (ANDR) can apply the SUDOKU outputs in the optimization of the engineered barriers of DFDSMA. 

European Partnership on Radioactive Waste Management (EURAD-2) is Co-funded by the European Union under Grant Agreement n° 101166718