Association of 137Cs and 239+240Pu with colloidal and suspended particulate material in shallow aquatic medium

Radionuclides are potentially transportable in shallow aquatic medium in association with the suspended particulate (4.1 μm) or colloids (<0.22μm - 2.1 nm). The purpose of the present study was to determine the distribution of total concentration of 137Cs and 239+240Pu in shallow aquatic system among colloidal and suspended- particulates. Laboratory simulated experiments were carried out by contaminating the water with 137Cs and 239+240Pu. Total concentration of 137Cs and 239+240Pu in unfiltered water were partitioned into suspended particulates by using conventional filtration assembly and colloidal components were concentrated with ultra-filtration stirred cell (Millipore make) ranging from < 0.22 μm to 2.1 nm in six different stages. Concentrations of 137Cs and 239+240Pu were measured in different fractions by using gamma and alpha (gross and spectrometric) counting techniques respectively. The major cations and anions in the aquatic medium were estimated by using Dionex-500 Ion Chromatography and GBC-932 Avanta Atomic Absorption Spectrometer. In the solution phase (filtered through 0.22 μm) 30% of 137Cs and 12% of 239+240Pu was observed. Among the colloidal fraction the maximum concentration of 137Cs and 239+240Pu is observed in fraction concentrated with 10,000 NMWL (Nominal Molecular Weight Limit). The concentration of 137Cs and 239+240Pu are found to be an order of magnitude high in above fraction. Efforts have been made to correlate the increase in concentration with some of the known inorganic colloids of aquatic system like Fe for Pu, and clay carbonate in case of 137Cs. (author)