Sediment particle size and initial radiocesium accumulation in ponds following the Fukushima DNPP accident

福島第一原子力発電所事故後の、ため池における放射性セシウムの初期蓄積と堆積物粒径について

吉村 和也  ; 恩田 裕一*; 福島 武彦*

Yoshimura, Kazuya; Onda, Yuichi*; Fukushima, Takehiko*

This study used particle size analysis to investigate the initial accumulation and trap efficiency of radiocesium (Cs) in four irrigation ponds, 4-5 months after the Fukushima Dai-ichi Nuclear Power Plant (DNPP) accident. Trap efficiency, represented by the inventory of Cs in pond sediment to the inventory of radiocesium in soil surrounding the pond (i.e., total Cs inventory), was less than 100% for all but one pond. Trap efficiency decreased as sediment particle size increased, indicating that sediments with a smaller particle size accumulate more Cs. In ponds showing low trap efficiency, fine sediment containing high concentrations of Cs appeared to be removed from the system by hydraulic flushing, leaving behind mostly coarse sediment.