Mortar matrices for radioactive waste materials physicochemical characterization in preageing tests due to addition of the polyethylene granules and powder

摘要

Powder and granules of the high density polyethylene (PEHD) were used to prepare mortar based matrices for immobilization of radioactive waste materials containing ~(137)Cs. PEHD powder and granules were added to mortar matrix preparatios with the objective of improving physicochemical characteristics of the radwaste-mortar matrix mixtures. PEHD granules were used to replace 100 volume percent of stone granules, normally used in the matrix. PEHD powder, particle size of 250 mum, was also added to the mortar formulation, replacing 5, 8 and 10 weight percent of the total cement weight in matrix formulation. Hardened orthocylindrical shaped samples, H=4.5 cm, have the exposed surface area completely open to contact liquid medium. Cured samples were investigated under normal and temperature stress conditions, in the accelerated ageing tests, where the temperature extremes were: T_(min)=-20~0 C, T_(max)=+70 deg C. Results of accelerated leaching experiments for all three types of samples were compared. Even using an accelerated ageing leacing test that overestimates ~(137)Cs leach-rates, it cna be deduced, that radionuclide leach-rates from the radioactive waste mortar mixture forms were improved, when polyethylene granules and powder are added in the mortar matrix. Leach-rates decreased from 4.8 percent, for the material prepared with stone aggregate to 3.35 for the materials prepared solely with PEHD granule,a nd to about 3 percents for the formulation made of PEHD granules and 8 weight percent of PEHD powder.