Evolution of surface concentrations of Sr and 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.*

This study attempts to reconcile the sources and relative inputs of Sr and Cs using the measured activities and their activity ratios of Cs/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, Cs/Sr ratios experienced a sharp increase before reaching an average of 391. 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.