Cs-134 and Cs-137 in the North Pacific Ocean derived from the March 2011 TEPCO Fukushima Dai-ichi Nuclear Power Plant accident, Japan. Part two: estimation of Cs-134 and Cs-137 inventories in the North Pacific Ocean

摘要

We estimated the inventories of radiocaesium released by the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident to the North Pacific Ocean by using compiled data and model simulations. By comparing the observed inventories with model-simulated results, we obtained 12-15 PBq of Cs-137 for the atmospheric deposition released by the FNPP1 accident in the North Pacific Ocean. Before the Fukushima accident, Cs-137 activity in the North Pacific Ocean was about 69 PBq. Therefore, the 12-15 PBq of Cs-137 newly added by atmospheric deposition together with the 3.5 +/- A 0.7 PBq added by direct discharge increased the total Cs-137 inventory in the North Pacific Ocean by 22-27 %. We also estimated the total amount of Cs-137 released to the atmosphere to be 15-20 PBq, and the total amount of Cs-137 released to the environment to be 19-24 PBq, respectively. Observed Cs-134 to Cs-137 activity ratio at the time of accident was close to 1 and extremely uniform, therefore, the total amount of Cs-134 deposition in the North Pacific Ocean, that of released to the atmosphere, that of direct discharge to the ocean and that of released to the environment were the same amounts as those of Cs-137.