[3E05-09] Environmental Radioactivity and Dose Assessment

[3E07] Long term behavior of radiocaesium and tritium off Fukushima

*Michio Aoyama¹ (1. Inst. of Environmental Radioactivity, Fukushima Univ.)

Keywords:radiocaesium, tritium, Fukushima Dai-ichi Nuclear Power Plant accident, water cycle

Radiocaesium and ³H data were examned in terms of temporal variation and ³H vs ¹³⁷Cs activity ratio and ¹³⁴Cs vs ¹³⁷Cs acticity ratio. The radiocaesium and ³H activity concentration in surface seawater close to the FNPP1 site showed decreaseing trend for both northward and southward in general. A temporal changes of direct release rates were different between ¹³⁷Cs and ³H. ¹³⁴Cs vs ¹³⁷Cs activity ratio in surface seawater off Fukushima showed excelent consistency which indicate that that main process during the transport is physical dilution by open ocean waters for both radiocaesium and ³H. It is however ³H vs. ¹³⁷Cs acticity ratio varied much which may indicate evaporation and contribution from river water/sporadic release of ³H rich water from the FNPP1 site.