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Oral presentation

Behavior of radiocesium at sediment-water interface off Fukushima

Otosaka, Shigeyoshi; Fukuda, Miho*; Aono, Tatsuo*

no journal, , 

Behavior of dissolved radiocesium near the seafloor is discussed from the distributions of $$^{137}$$Cs in overlying water (seawater collected from $$sim$$30 cm above the seabed) at 14 stations and in pore water at 3 stations off Fukushima (1$$sim$$70 km from Fukushima Daiichi Nuclear Power Plant). The $$^{137}$$Cs concentrations in overlying water, collected during 2015 and 2016, ranged between 5 and 283 mBq/L. The $$^{137}$$Cs concentrations in overlying water were 2$$sim$$3 times higher than those in seawater collected from intermediate (5 m above the bottom) layers. The $$^{137}$$Cs concentrations in pore water were 10$$sim$$30 times higher than those in overlying water. We can consider that radiocesium is dissolved in the overlying water and has been diffused from the seabed through the porewater. Nevertheless, it was estimated that the amount of $$^{137}$$Cs transferred from porewater to benthic organisms does not lead to $$^{137}$$Cs activities exceeding the regulation limits at most stations.

Oral presentation

Evolution of surface concentrations of $$^{90}$$Sr and $$^{137}$$Cs through 2016 from the Fukushima Dai-ichi nuclear accident

Kenyon, J.*; Buesseler, K. O.*; Casacuberta, N.*; Castrillejo, M.*; Otosaka, Shigeyoshi; Drysdale, J.*; Pike, S.*; Juan Diaz, X.*

no journal, , 

This study attempts to reconcile the sources and relative inputs of $$^{90}$$Sr and $$^{137}$$Cs using the measured activities and their activity ratios of $$^{137}$$Cs/$$^{90}$$Sr off the coast of Japan. Pre-accident levels correlate with 1960's weapons testing fallout activity ratios of 1.6. Immediately following the accident, $$^{137}$$Cs/$$^{90}$$Sr ratios experienced a sharp increase before reaching an average of 39$$pm$$1. Data from 2011 to 2016 off the coast of Japan show that radionuclide concentrations since the accident have been decreasing, but are not yet comparable to pre-accident levels in the areas immediately surrounding FDNPP. Areas farther away from FNDPP show ratios closer to pre-accident waters, giving insight to the transport and mixing of water off the coast of FDNPP. We observe that the release of radionuclides from FDNPP is ongoing, but at rates more than one thousand times lower than initial releases in 2011.

Oral presentation

Effects of pH on the formation and transformation of Fe(II)-Si coprecipitates under anoxic, reducing conditions

Francisco, P. C. M.; Mitsui, Seiichiro; Ishidera, Takamitsu; Tachi, Yukio

no journal, , 

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