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

This study used particle size analysis to investigate the initial accumulation and trap efficiency of radiocesium (Cs-137) in four irrigation ponds, similar to 4-5 months after the Fukushima Dai-ichi nuclear power plant (DNPP) accident. Trap efficiency, represented by the inventory of Cs-137 in pond sediment to the inventory of radiocesium in soil surrounding the pond (i.e., total Cs-137 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-137. In ponds showing low trap efficiency, fine sediment containing high concentrations of Cs-137 appeared to be removed from the system by hydraulic flushing, leaving behind mostly coarse sediment. The results of this study suggest that sediment particle size can be used to estimate the initial accumulation and trap efficiency of Cs-137 in pond sediment, as well as the amount lost through hydraulic flushing.