Mixing of waters released from Fukushima with uncontaminated seawater will lead to a rapid decrease in the concentrations of levels of radionuclides.
On short time scales mainly I-131 will be of concern due their possible enrichment in the marine food chain.
On long time scales Cs-137 (T 1/2 =30 y) Sr-90 (T 1/2 =29y) and Cs-134 (T 1/2 =2 y) will be of concern due to their longer half-lives, thus these radionuclides will be transported over long distances by ocean currents.
It can be expected that the marine dispersion of seawater tagged with radionuclides released from Fukushima will take months or years to reach other riparian Pacific countries.
Presently atmospheric transport over long distances is the main spreading (transport) pathway of contaminats
Seawater sampling off Fukushima (21-23 March 2011)
Seawater sampling locations
Near field: 330m south of discharge point
Transect about 30 km offshore, 8 sample locations separated by 10 kilometres
According to Japanese authorities, no particular action had been taken at this moment concerning fishing outside the evacuation zone.
Seawater sampling off Fukushima (24 March 2011)
Seawater sampling locations
Repetition of the transect about 30 km offshore at the 24 th March
Levels of dose rates are included
First preliminary modelling results
Initiated by the Monaco Laboratory at the SIROCCO Group of the Université de Toulouse / CNRS
Source term needed
high resolution 3D Ocean model (600*600m)
Model input :
Global oceanic information from MERCATOR (World Ocean Forecast)
Global meteorological from ECMWF (Europe Weather Forecast)
Tide information from T-UGO
Model Output : Coastal circulation, Particles dispersion …
Objective: Simulation of radionuclide dispersion in seawater Atmospheric released from Fukushima Power plant
More realistic results require:
Source term atmospheric and liquid
Atmospheric deposition pattern.
Measurement data for model validation
First results: - North-eastward dispersion - Surface of 150*300 km 2 reach in 11 days March, 22
Model started the March, 12
Particles Input: Hypothetical Unit Release ( instant contamination on a 30 km radius off-shore)
6 days forecasting of particles dispersion in the marine environment
Hypothetical Unit Release instant atmospheric contamination
Measurements have been carried out by Japanese Institutes at 30 km off-shore in a south-north section at the 22nd/23rd March. Results were made available at 24th March.
I-131 and Cs-137 were detected with highest activity concentration of about 80 Bq/L and 24 Bq/L in surface layer, respectively.
It can be assumed that this contamination is due to atmospheric fallout by dry or wet deposition and not only by the ocean currents.
Dilution, both into deeper layers and by dispersion along the preveailing ocean currents will lead to rapid decrease of the initial surface contamination.
For short term, I-131 will be the relevant radionuclides as far as doses are concerned, for long term, Cs-137 will be the more important radionuclide in the marine environment. Due to its relatively conservative behaviour in seawater, it will be possible to follow this nuclide over long distances for several years.
Modelling of the dispersion of radionuclides has been initiated and first results are available.
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.