Leaching Behavior of Cesium-137 in Cement-waste Composites

Abstract

To assess the safety for disposal of a radioactive waste-cement composite, the leaching of I3'Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA. The leachability was measured as functions of waste to cement ratio (Wa/C), concentration of the salt (Na,SO,), temperature of leachant and curing time of specimens.The fraction of 137Cs leached from a specimen of Portland cement is 0.3-0.4 at the leaching time of 100 days, whereas the corresponding value for a specimen of slag cement is 0.1-0.15. The leachability depends on the structure of cement composite which is influenced by such factors as Wa/C, salt concentration of the wastes, and curing time of the specimens. The leach coefficient of '37Cs increases with increasing porosity of the cement composite. At lower temperature, curing time of the specimens significantly affects the leachability, probably due to insufficient curing. A curing time of ca. 50 days before the leaching test is enough to eliminate the apparent effect of temperature.

Mathematical Modelling of Immobilization of Radionuclides 137Cs and 60Co in Concrete Matrix

“…Leaching mechanism can be classified into two general categories: 1) initial wash off and 2) diffusion control. On the basis of parameters A 1 and leaching coefficient D e [8], in different cement matrix formulations, we have noticed that leaching rate of Cs 137 > Co 60 which is matched with other studies [1][2][3][4]. We have also observed that Cs 137 and Co 60 cumulative amount of leached, f, decreased in order f (C-II) > f (C-IV) > f (C-I) > f (C-III).…”

“…The dispersion of radionuclides in porous materials, such as grout or concrete, is described using a one dimensional differential model [1][2][3].…”

“…The hydrated cement will contact water and generate conditions that constitute a long-term chemical barrier to radionuclide migration as a result of decreased solubility and strong adsorption. The transport rate through engineered barriers is mainly diffusion controlled, but due to the strong sorption behaviour of the materials, the diffusion rate of the radionuclides is much slower than in pure water [1][2][3][4].…”

Mathematical modelling of transport phenomena in concrete porous media

“…Th ree methods are compared with respect to their applicability to experimental leaching data [6,10,13,14].…”

“…A szivárgási vizsgálatot a Vinca Intézet által kifejlesztett eredeti módszerrel [1, 2, 3, 4, 5] végeztük. A radioaktív anyag egy cementes kompozit mátrixból való kiszivárgásának szállítási jelenségeit az elméleti egyenleteken [6,10] alapuló három módszer alkalmazásával vizsgáltuk. Ezek a következők voltak: egy sima forrásra vonatkozó diffúziós egyenlet, egy első fokú egyenlettel párosított diffúziós egyenlet, és egy polinom egyenletet használó empirikus módszer.…”