Cementitious mortar for Intermediate and Low-Level Radioactive waste confinement: matrix optimization and leaching

A cement-based mortar prepared utilizing a pozzolanic cement (CEM IV/A 42.5 R type conforming to European Standard EN 197–1) was optimized for the containment of Intermediate and Low-Level Radioactive Waste without the use of expensive additives. Surrogate radionuclides, including lithium (Li), cesium (Cs), cobalt (Co), and lead (Pb) salts, were incorporated to simulate real waste streams. The experiments focused on optimizing the water-to-cement ratio, the sand-to-cement ratio of the mortar, and assessing the effects of simulated radionuclide addition on its properties. At the investigated level of adding radionuclides (2.5 mmol/kg), the mortar maintained a compressive strength of approximately 54 N/mm2, while water absorption and workability remained unchanged with respect to the reference. However, thermogravimetric analysis and Fourier-transform infrared spectroscopy indicated that radionuclides interfered with the hydration reaction. Leaching tests on hardened monolith specimens demonstrated varying radionuclide mobilities, with the following order: Li > Cs > Co > Pb. In all cases, the leachability index was greater than 8, confirming effective containment. Diffusion was identified as the controlling mechanism for all simulated radionuclides except Pb, for which wash-off dominated the release process. These results confirm that CEM IV/A based mortar is an effective material for immobilizing radionuclides, maintaining mechanical integrity while limiting radionuclide migration.