Seven-year Temporal Variation of Cesium-137 Discharge Inventory from the Port of Fukushima Dai-ichi Nuclear Power Plant:

Suspended Particle–Water Interactions Increase Dissolved 137Cs Activities in the Nearshore Seawater during Typhoon Hagibis

“…This comparison is enough to evaluate to what extent the desorbed 137 Cs from riverine suspended particles affects the dissolved 137 Cs levels in the nearshore waters during the typhoon because the typhoon Hagibis is the largest one since 1976, as suggested in the Methods and Materials section of the Supporting Information. According to respective estimation from previous studies, the ongoing release was 0.2−2.1 TBq/ year during the year period of 2012−2016, 15 re-entry through the SGD was 0.2−1.1 TBq/year (0.55−3.0 GBq/day) during the year period of 2013−2016, 16 and input of desorbed fraction from riverine particles was 0.04−0.4 TBq/year (0.11− 1.1 GBq/day), which was calculated based on the f (0.03−0.3) in this study and 1.2 TBq/year (3.3 GBq/day) of riverine particulate 137 Cs in only the Abukuma River (2012−2015). 23 Apparently, the ongoing release from the FDNPP is the main source during the year period, while this input fell into 0.13− 0.16 TBq in 2017.…”

“…Our calculations indicate that desorption of 137 Cs may not account for all of the increase in dissolved 137 Cs activity in nearshore waters (Figure 4A). The remainder of the increase may have been due to ongoing release 15,48 and probably continuous 137 Cs re-entry via groundwater. 16 We evaluated the contribution of the 137 Cs input to the coastal area from three sources (ongoing release from FDNPP, 15 re-entry through the SGD associated with beach sands, 16 and input of desorbed fraction from riverine particles (e.g., Abukuma River) during the year period of 2012−2016), as shown in Figure 1, although the sampling period was different from that in this study.…”

“…The remainder of the increase may have been due to ongoing release 15,48 and probably continuous 137 Cs re-entry via groundwater. 16 We evaluated the contribution of the 137 Cs input to the coastal area from three sources (ongoing release from FDNPP, 15 re-entry through the SGD associated with beach sands, 16 and input of desorbed fraction from riverine particles (e.g., Abukuma River) during the year period of 2012−2016), as shown in Figure 1, although the sampling period was different from that in this study. This comparison is enough to evaluate to what extent the desorbed 137 Cs from riverine suspended particles affects the dissolved 137 Cs levels in the nearshore waters during the typhoon because the typhoon Hagibis is the largest one since 1976, as suggested in the Methods and Materials section of the Supporting Information.…”

“…A sharp decline in radionuclide releases with water from the FDNPP after completion of a frozen soil wall in 2015 and of the water treatment system (e.g., pumping up the polluted water) 17 was probably the result of a reduction in the flow from the FDNPP because the flux from the plant has been decreasing since then. 15 Hence, it is likely that the constant flux of 137 Cs from rivers, the catchment areas of which are contaminated, now plays a more important role in the activities of 137 Cs in coastal areas in addition to the re-entry of 137 Cs from sediments through SGD, which increases dissolved 137 Cs in coastal waters of the wide area from both north and south of the FDNPP. 16 This hypothesis is supported by the evidence that 137 Chernobyl nuclear power plant (CNPP) accident were higher than those in the North Atlantic Ocean several decades later.…”

“…Particularly, we focus on to what extent the desorbed fraction of riverine radiocesium contributed to the elevated levels of 137 Cs in the dissolved phase in the nearshore areas after the heavy rainfall from typhoon Hagibis in the middle of October 2019. For this purpose, from the 137 Cs fluxes from different sources (the ongoing release from the FDNPP, 15 re-entry through the SGD associated with beach sands, 16 and desorption from riverine particles by exposure to seawater; Figure 1) are analyzed and compared.…”