March 21, 2011, (March 19 release).
Simulations of atmospheric dispersion of the plume formed by the release of the Fukushima Daiichi Nuclear Power Station, between March 12 and March 20, 2011
1 - What is known radioactive releases issued since March 12, 2011?
The IRSN has no direct measurement data on the composition and extent of radioactive releases, but has technical information on facilities rugged.
The interpretation of this information has enabled the IRSN to develop likely scenarios of degradation of three reactors since March 12, ensuring their consistency with the measurements of dose rate obtained on the site. IRSN also retained the assumption that these discharges will continue until March 20.
The radioactive elements released during various episodes of rejection are rare gases (radioactive elements chemically very reactive, remaining in the atmosphere without being deposited on the ground) and volatile elements, mainly from radioactive iodine, including iodine-131 which has a half life of 8 days, and radioactive cesium, which cesium 137.
2 - The dispersion of radioactive releases into the atmosphere
IRSN simulated atmospheric dispersion of releases estimated between 12 and 22 March, using its numerical model applicable to long distance (scale of several hundred kilometers), using observations and weather forecasts provided by Weather France.
This simulation was applied to the cesium 137, as a tracer of the plume during this period. The modeling results are expressed in becquerels of cesium-137 per cubic meter of air (Bq / m 3):
Watch the simulation of the plume
IRSN compared the simulation results with the results of measurements of air contamination carried in Tokyo. They are the same order of magnitude as the values measured in this city, as shown in the charts below for iodine 131 and cesium 137.
This comparison allows us to consider that the air dispersion modeling performed by IRSN to produce satisfactory results for the agglomeration of Tokyo and the doses calculated by IRSN from this modeling are representative of the doses may have been received by the population exposed to the radioactive plume.
Evolution of the activity of Cesium 137 and Iodine 131 measured in air of Tokyo March 15 to 17 (local time)
Concentration of Cesium 137 and Iodine-131 in the air of Tokyo calculated by IRSN by modeling the long-range atmospheric dispersion
3 - Estimation of doses likely to be received by persons exposed to the radioactive plume
IRSN said the doses likely to be received by a person exposed to the radioactive plume, assuming it stays in one place and unprotected (outside) from March 12 to 22. For these dose calculations, the SNRIs considered a child of a year which is most sensitive to iodine 131 (thyroid dose).
The following simulations show the evolution of doses over time, the simulation period. If new releases were to occur in the future, these rates may increase further in the absence of protection for those most at risk.
Whole body dose may be received by a child of 1 year in the absence of protection for releases:
Watch the simulation
In case of accident, the values of whole-body doses from which protective actions are recommended are 10 mSv for sheltering in place and 50 mSv for evacuation. Below 10 mSv, the health risk is considered low enough not to make the necessary protective actions. For comparison, the average annual dose received in France due to natural radioactivity and medical exposure is 3.7 mSv.
Thyroid doses could be received by a child of 1 year in the absence of protection for releases:
Watch the simulation
In case of accident, the dose values from which the ingestion of stable iodine is recommended in Japan is 100 mSv.
4 - Modeling the dispersion of radioactive releases into the atmosphere on a global scale
From the estimated releases from IRSN, Meteo France has simulated the dispersion of radioactive releases from great distances, projected until March 26:
Merger expected to run from this model could be of the order of 0,001 Bq / m 3 in France and the overseas departments of the northern hemisphere. As expected, the southern hemisphere is not significantly affected by this large-scale dispersal.
For comparison, values measured in the days following the Chernobyl accident had exceeded 100 000 Bq / m 3 in the first few kilometers around the plant and they were in the range of 100 to 1000 Bq / m 3 in the country most affected by the plume (Ukraine, Belarus); France, values measured in the east were the order of 1 to 10 Bq/m3 (May 1, 1986). Today, a very low activity of cesium-137 remains in the air, on the order of 0.000001 Bq/m3.
Monitoring of radioactivity in the air in France
IRSN provides several maps to obtain the results of measurement of radioactivity in air:
- In France: http://www.irsn.fr/FR/Documents/france.htm
- To Saint Pierre et Miquelon: http://www.irsn.fr/FR/Documents/Saint-Pierre-et-Miquelon.htm
- Tahiti: http://www.irsn.fr/FR/Documents/Tahiti.htm
- Guyana: http://www.irsn.fr/FR/Documents/guyane.htm
- Guadeloupe: http://www.irsn.fr/FR/Documents/guadeloupe.htm
- In Martinique: http://www.irsn.fr/FR/Documents/martinique.htm
- La Reunion http://www.irsn.fr/FR/Documents/lareunion.htm
- In New Caledonia: http://www.irsn.fr/FR/Documents/nouvelle-caledonie.htm
For more informations about IRSN, visit (in French): http://www.irsn.fr/FR/Documents/home.htm
Images, Animations, Text, Credit: Institute of Radiation Protection and Nuclear Safety (IRSN) / Météo France / Translation: Orbiter.ch.
NB: The IRSN is not responsible for any incorrect translations.
Greetings, Orbiter.ch
