This paper reports results from an investigation of the carbonation effects on a cement-solidified matrix. The water-cement compositions were solidified using ordinary Portland cement (OPC) and cured at 20 oC and 100% humidity for 28 days. Then the samples were investigated for stability in the water phase at different temperatures and experimental conditions: stationary, flow and circulation of the water phase. The DTG and X-ray diffraction (XRD) analyses were used for the investigation of the carbonation processes of the water/cement solidified matrix. Carbonated solidified products from the stationary experiments were characterized by enhanced aragonite, vaterite and calcite contents, higher strength values and a significant reduction in leachable 137Cs extracted, compared to flow and circulation experiment samples.