Radioactive waste-mortar mixture form characterization due to its physico-chemical and mechanical properties obtained in an accelerated and non-accelerated leaching process

Mortar as a matrix for the radioactive waste materials of the low and intermediate level of bonded activity is investigated in the ''Vinca'' Institute in accordance with IAEA standardized procedures and recommendations. One of the properties that could characterize mortar as an appropriate matrix for radioactive waste materials accept of the most commonly used radionuclide leach rate is its mechanical strength. In the performed experiments two groups of the orthocylinder shaped mortar matrix samples doped with 137CsCl solution, after curing in the atmosphere of defined parameters for 28 days were treated on leaching in distilled water using accelerated and non-accelerated processes. The first group of samples was treated on leaching for period of 292 days in aim to obtain cumulative 137Cs leached fraction. 137Cs leach rate of such treated samples, was a base in establishing cycles for accelerated ageing processes, that understands samples immersion, heating, immersion and freezing in each cycle. The second group of samples was treated on leaching using cycles in accelerated ageing of mortar matrices. By introducing the mortar-radioactive waste mixture form into the environment with temperature extremes, we could obtain the radionuclide 137Cs leach-rate, that is adequate for the nearly one year non-accelerated leaching conditions in the almost eight cycle steps of the accelerated ageing process. Mechanical strength of such treated samples was investigated using hydraulic press. Decreasing of the empirically obtained values for mechanical strength of samples treated by accelerated and standardized Hespe leaching method were noticed, being consequence of the corrosion effects of water on mortar and synergistic influence of mortar matrix exposure to the elevated temperatures before each immersion step. These experiments were performed in aim to predict mortar matrix behaviour due to leaching and mechanical characteristics in the prolonged periods of disposal, assuming the most undesirable environmental conditions on the disposal site. (author). 3 refs, 2 figs, 2 tabs