Capability of the Kd model to predict radionuclides behaviour and transport in unsaturated columns under steady flow conditions

Abstract

Abstract. In the frame of the IRSN Chernobyl Pilot Site Project, a waste trench containing hot particles was instrumented to study the fate of radioactive pollutants. Cs in the Aeolian sand in both saturated and unsaturated conditions. Batch experiments were performed to study the chemical equilibrium state of the soil/solution system under static conditions. Stirred flow-through reactor experiments were performed to study the kinetics and reversibility of sorption reactions at the surface of solid particles under dynamic conditions. Column experiments in the structured porous media were also performed in saturated and unsaturated flow conditions. Experimental data pointed out a non-linear, instantaneous and reversible sorption process of 90 Sr. 137Cs exhibits a non-linear behaviour with a partial irreversible sorption process. A suitable cation-exchange model was used to describe the solute/soil reactions. The former model was coupled with transport models to describe behaviour of 90 Sr and 137 Cs in both saturated and unsaturated steady flow conditions. Main transport parameters were identified and discussed. An effective simple Kd type approach to describe radionuclides transport properties under unsaturated conditions was evaluated.

Do transient hydrological processes explain the variability of strontium-90 activity in groundwater downstream of a radioactive trench near Chernobyl?

“…The flowand-transport model shows that this migration can be reproduced by considering reversible 90 Sr sorption processes within both waste material and underlying sand, e.g., through the linear equilibrium sorption concept, combined with a vertical percolation flow. The reversibility of the 90 Sr sorption in the Chernobyl eolian sandy deposit was already highlighted through laboratory experiments (Ardois and Szentnect, 2005). These experiments also showed that the 90 Sr sorption can be perfectly described by the same ion exchange model whatever the water content.…”

Influence of non-equilibrium sorption on the vertical migration of 137Cs in forest mineral soils of Fukushima Prefecture

“…These empirical models mitigate the Kd hypothesis by assuming that sorption occurs on 2-3 different types of solid sites, governed by equilibrium and/or kinetic rates. In the laboratory, the EK approaches better describe non-equilibrium 137Cs sorption observed in batch sorption experiments (Lee et al, 2013;Valcke and Cremers, 1994), stirred flow-through reactors, and soil columns (Ardois and Szenknect, 2005;Szenknect et al, 2003). However, in field conditions, evidences that equilibrium-kinetic sorption explain observed 137Cs migration are still limited.…”