ABSTRACTThe rutile form of titanium dioxide (TiO2) and granules of high
density polyethylene (PEHD) and low density polyethylene (PELD) were used to
prepare mortar matrices for immobilization of radioactive waste materials
containing ‘137Cs. PELD,PEHD and TiO2 were added to
mortar matrix preparations with the objective of improving physico-chemical
characteristics of the radwaste-mortar matrix mixtures, in particular the
leach-rate of the immobilized radionuclide. The diameters of the PELD and
PEHD used varied from 0.2 to 2.0 mm. One type of PELD and two types of PEHD
were used to replace 50 weight percent of stone granules, average diameter
of 2 mm, normally used in the matrix, in order to decrease the porosity and
density of the mortar matrix and to avoid segregation of the stone particles
at the bottom of the immobilized radioactive waste cylindrical form.
TiO2 was also added to the mortar formulation, replacing 5 and
8 weight percent of the total cement weight, for each PEHD and PELD
formulation. Cured samples were investigated under temperature stress
conditions, where the temperature extremes were: Tmill =
-20°C,Tmax= +70°C. Samples were periodically immersed in
distilled water at the ambient room temperature, after each freezing and
heating treatment. Results of accelerated leaching experiments for these
samples and samples prepared exclusively with polyethylenes replacing 100
percents of the stone granules and TiO2, treated in
nonaccelerated leaching experiments, were compared. Even using an
accelerated ageing leach test that overestimates 137Cs leach
rates, it can be deduced, that radionuclide leach rates from the radioactive
waste mortar mixture forms were improved. Leach rates decreased from 5
percent, for the material prepared with stone aggregate, to 3.1 to 4.0
percent, for the materials prepared solely with PEHD, PELD or
TiO2, and to about 3 percents for all six types of the
TiO2-PEHD and TiO2-PELD mixtures tested.
Preparation and properties of low density polyethylene-activated carbon composite foams