Assessment of Dry and Wet Atmospheric Deposits of Radioactive Aerosols: Application to Fukushima Radiocaesium Fallout

Abstract

The Fukushima Dai-ichi nuclear accident led to massive atmospheric deposition of radioactive substances onto the land surfaces. The spatial distribution of deposits has been estimated by Japanese authorities for gamma-emitting radionuclides through either airborne monitoring surveys (since April 2011) or in situ gamma-ray spectrometry of bare soil areas (since summer 2011). We demonstrate that significant differences exist between the two surveys for radiocaesium isotopes and that these differences can be related to dry deposits through the use of physically based relationships involving aerosol deposition velocities. The methodology, which has been applied to cesium-134 and cesium-137 deposits within 80-km of the nuclear site, provides reasonable spatial estimations of dry and wet deposits that are discussed and compared to atmospheric numerical simulations from the Japanese Atomic Energy Agency and the French Institute of Radioprotection and Nuclear Safety. As a complementary approach to numerical simulations, this field-based analysis has the possibility to contribute information that can be applied to the understanding and assessment of dose impacts to human populations and the environment around Fukushima.

Initial radiocesium deposition on forest ecosystems surrounding the Tokyo metropolitan area due to the Fukushima Daiichi Nuclear Power Plant accident

“…However, in previous studies, during similar periods after each accident the cumulative radiocesium deposition by TF were not higher than those of BP (Bunzl et al, 1989;Kato et al, 2012). The contribution of dry deposition to radiocesium contamination was estimated recently in the area surrounding FD1NPP which indicated significant spatial variability (Gonze et al, 2014). The contribution from dry deposition at our site could be the reason for the difference to deposition rates observed in previous studies.…”

Characteristics of initial deposition and behavior of radiocesium in forest ecosystems of different locations and species affected by the Fukushima Daiichi Nuclear Power Plant accident

“…It was reported that Table 3 The 137 Cs stock (Bq m À2 ) in the aboveground and belowground components in the study plots. the wet fraction of 137 Cs deposition (the proportion of wet to total deposition) was variable by sites (Gonze et al, 2014;Korsakissok et al, 2013). According to the map produced by Gonze et al (2014), the proportion of wet 137 Cs fraction reaches more than 80% of the total deposition at the OT site, whereas it remains 40e60% at the KU site.…”

“…the wet fraction of 137 Cs deposition (the proportion of wet to total deposition) was variable by sites (Gonze et al, 2014;Korsakissok et al, 2013). According to the map produced by Gonze et al (2014), the proportion of wet 137 Cs fraction reaches more than 80% of the total deposition at the OT site, whereas it remains 40e60% at the KU site. Another evaluation report on the initial 137 Cs contamination indicates that the western part of Fukushima including the TD site experienced primarily wet 137 Cs deposition (Nagai et al, 2014).…”

Radiocesium transfer from hillslopes to the Pacific Ocean after the Fukushima Nuclear Power Plant accident: A review

“…3). There are multiple approaches to quantify catchment radiocesium inventories including both airborne and soil sampling surveys (Gonze et al, 2014;Yoshida and Takahashi, 2012). As this review examines the transfer of radiocesium from hillslopes to the Pacific Ocean, we used soil sampling surveys to quantify the total, mean, and standard deviation of radiocesium ( 134 Cs þ 137 Cs) fallout in 14 coastal catchments of the Fukushima region (Fig.…”

“…Although quantifying catchment inventories with airborne and soil based sampling techniques or different spatial interpretation approaches may yield different results (Gonze et al, 2014), what is important to the research and management community is the spatial distribution of radiocesium. In particular, characterizing the deposition of radiocesium, especially the different catchments and landscapes receiving the fallout (e.g different forest types), is important for understanding the sources and spatial distribution of radiocesium available for transfer from hillslopes to the Pacific Ocean.…”