Migration Behavior of Carbonate- 14 C in Tuffaceous Soil
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MIGRATION BEHAVIOR OF CARBONATE-
14
C IN TUFFACEOUS SOIL
S. NAGAO AND M. SENOO Department of Environmental Safety Research, Japan Atomic Energy Research Institute, Tokaimura Naka-gun Ibaraki-ken 319-11, Japan
ABSTRACT A simple closed column system was developed to study migration of bicarbonate and 14 14 carbonate C in soil layer. Experimental data for glass beads having less the C adsorption 14 indicate that the system can be performed on column experiment keeping mass balance of C. 14 C in a tuffaceous sandy soil was Migration behavior of bicarbonate and carbonate 14 C was delayed to investigated by this column system in the pH range from 8 to 12. The tritiated water, and the retardation became stronger in order, pH 12 < pH 10 < pH 8. This is considered to be due to pH-dependent adsorption of bicarbonate and carbonate ions onto the soil sample. INTRODUCTION Carbon-14 (14C) occurs in nature, but is also formed at nuclear power plants. Because of 14 its long half-life (5730 years) and biological significance of carbon, releases of C from nuclear facilities could have a significant radiological impact [ 1]. Bicarbonate and carbonate are 14 major chemical forms of inorganic C in low level radioactive waste [2]. The most likely mode of release of 14C from a geologic repository is by aqueous leaching [2]. Study on migration of bicarbonate and carbonate 14C in underground layer is important to evaluate environmental safety assessment for underground disposal of radioactive waste. Column experiments are one of most useful methods to study migration of radionuclides in soil layer. Retardation of radionuclides can be evaluated by this method. Studies on the 14 experiments, C in underground layer by column migration of bicarbonate and carbonate 14 C, the claim has however, are not numerous [3,4]. In many experimental cases involving 14 been made that considerable loss of C and/or C02 in the media can take place by exchange with atmospheric C02. In order to assess the retardation accurately, it is important to keep mass balance of 1 4 C in the column system before and after the experiments. The purpose of this study is to establish a simple closed column system keeping mass balance of 1 4 C and using the method of constant feed of radiotracer. The column system was designed to make it air-tight from reservoir bottle to soil column. We have checked the release 14 and adsorption of C respect to the column system by the column packed with glass beads. This method was applied to a tuffaceous sandy soil, as a porous media of geological materials, 14 and studied on the migration behavior of bicarbonate and carbonate C in the pH range from pH 8 to 12. The desorption experiments were carried out with the column system by distilled 4 water and NaF treatments to study the adsorption mechanisms of 1 C. MATERIALS AND METHOD
Materia Glass beads were purchased from Toshiba Barotini Co. Ltd. and used to check release 14 and adsorption of C on the column system during experiments because of relatively uniform 14 C (distribution coeffic
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