六ヶ所村汽水湖尾駮沼における表層堆積物中の放射性核種¹³⁷Csの濃度と存在形態

抄録

To determine the recently accumulated state of the radiocesium¹³⁷Csin surface sediment in the brackish-water Lake Obuchi, surrounded by facilities reprocessing spent nuclear fuel in Rokkasho Village, we investigated concentration of¹³⁷Csin the sediment and speciation of¹³⁷Csin the sediment according to standard procedures of sequential extraction. Concentrations of¹³⁷Csin the sediment, the silty types (8.0 -13.8Bq kg^-1dry) were higher than the sandy type (0.2Bq kg^-1dry) . Concentrations of¹³⁷Csin the sediment tended to be higher in the smaller particle sizes. Moreover, we observed a high correlation coefficient between¹³⁷Csconcentration in the sediment and amount of organic matter. We found that most¹³⁷Csin the sediment were the speciations (contained within the crystal structures of minerals etc.) that non-eluted under a natural condition; however, the¹³⁷Csbonded to organic matter in the sediment were only about 5 % of the sum total of each extraction. This suggests that organic matter acts as a carrier in¹³⁷Csaccumulation on the lake bottom. Also, ¹³⁷Csin the sediment can more readily exist in a stable state when bonded to minerals, possessing a crystal structure, rather than to organic matter.