Measurements of the marine environment was carried out by Japanese authorities since 23 March and data reported to the IAEA for information and assessment.
Measurement were done at 30 km off-short section on 8 locations, on 26 March on 4 Stations.
I-131 and Cs-137 were detected with highest activity concentration of about 80 Bq/L and 26 Bq/L in surface layer, respectively, at the 23 and 24 March.
Data were reported for 26 March and they show now decreasing trend between 6 and 18 Bq/L for I-131 and „not detectable“ and 16.4 Bq/L for Cs-137.
Dose rates were also given above seawater level on 26 March. They are between 0.041 and 0.100 micro-Sv/h
Levels at about 330 m east of the discharge area showed increasing concentrations with 74000 Bq/L for I-131, 12000 Bq/L for both radionuclides Cs-134 and Cs-137
Modelling of the dispersion of radionuclides was initiated and first results were available. The results show an initial transport into north-east direction and the contaminated seawater could reach the 30 km off-shore sampling section between 7 and 14 days after release
It can be expected that the marine dispersion will take months or years to reach other riparian Pacific countries. At resent, the main transport of contamination takes place by atmospheric transport over long distances with high dilution capacity.