Migration of Anionic Species of Radioactive Cobalt through Soil
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MIGRATION OF ANIONIC SPECIES OF RADIOACTIVE COBALT THROUGH SOIL Toshihiko OHNUKI* and David E. ROBERTSON*" Department of Environmental Safety Research, Japan Atomic Energy Research Institute, Shirakata, Tokai, Japan ** Chemical Science Department, Pacific Northwest Laboratories, Richland, WA, 99352, USA. *
Ibaraki,
319-11,
ABSTRACT The migration of an anionic species of 6 0 Co through soil has been examined utilizing data on the migration of radionuclides leached from an aqueous waste disposal site. Correlation coefficients between concentrations of the anionic species of 6 0 Co and those of the particulate, 60 cationic and non-ionic species of Co reveal that the anionic species of 60 Co was not interconverted from the other species during migration. The cross correlations of changes in the concentrations of the anionic species 60 of Co with time between three different down gradient positions give a calculated retardation factor of the anionic species of 6 0 Co of approximately 19, being 1200 times lower than the results of laboratory measurements. The average concentration distribution of the anionic species of 6 0 Co suggests that the migration of the anionic species of 6 0 Co consists of two migration fractions which were driven by different migration mechanisms. INTRODUCTION It is important to estimate the impacts of radioactive wastes deposited at disposal sites. The migration of radionuclides through soil is one of the critical paths for mobilizing radionuclides from a disposal site to the environment [1,2]. One of the most abundant radionuclides contained in low-level wastes generated in nuclear power plants is 6 06Co. Thus, many research scientists have investigated the migration of 0 Co through soil [e.g. 3,41. The cobalt in groundwater solution of low and neutral pH is adsorbed by soil [5,6]. This suggests that the 6 0 Co leached from disposal sites not migrate through soil at high speeds. However, a small portion of 6does 0 Co leached from several radioactive aqueous waste disposal sites migrated at nearly the same speed as the water velocity through the soil [7,8]. The chemical species of the mobile 6 0 Co is non-cationic in nature. The 60 migration behavior of an anionic or neutral species of Co is different 60 from that of a cationic species of Co 19,10]. Therefore, it is important to elucidate the migration behavior of an anionic species of 6 0 Co in soil. The chemical species of 6 0 Co leached from a radioactive aqueous waste disposal site have been investigated [11-13]. In these analyses, 6 0 Co was separated into particulate, cationic, anionic and non-ionic species, and the concentration of each chemical species of 6 0 Co was measured with time at several different positions along the groundwater stream. The studies showed that the mobile species of 6 0 Co was anionic in form. Unfortunately, the migration behavior of the anionic species of 6 0 Co have not yet been studied in detail. Therefore, the migration of the anionic species of 6 0 Co through soil has been studied by analyzing this data b
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