Friday, March 18, 2011

Fukushima: 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

From the French Radiation Protection Agency:

1 - What is known radioactive releases issued at March 12, 2011 then?

The IRSN has no direct information on the composition and extent of radioactive releases. The interpretation of dose rate measurements on site and the likely scenarios of degradation of three reactors since March 12, assuming that these releases will continue until 20 March. The radioactive elements released during various episodes of rejection are rare gases (radioactive elements chemically unreactive, 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. The proportions of the different radioactive elements into account general knowledge about nuclear reactors. 
2 - The dispersion of radioactive releases into the atmosphere

IRSN simulated atmospheric dispersion of releases estimated between 12 and 20 March, using its numerical model applicable to long distance (scale of several hundred kilometers), using weather forecasts provided by Météo France .
This simulation was applied to the cesium 137, as a tracer of the plume during this period. The results of this simulation, conducted every hour from 12 March, are expressed in becquerels of cesium-137 per cubic meter of air (Bq / m 3). For comparison, values ​​measured near the Chernobyl plant, shortly after the accident on April 26, 1986, exceeded 100 000 Bq / m; they were in the range of 100-1000 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.

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) for the duration of discards (from March 12 to 20 ). For these dose calculations, the SNRIs considered a child of a year which is most sensitive to iodine 131 (thyroid dose). It is therefore prudent assumptions.
The following simulations show the evolution of doses over time, the simulation period. If no new discharges would 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

In case of accident, the dose values ​​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  

In case of accident, the dose values ​​from which the ingestion of stable iodine is recommended is 100 mSv in Japan.

1 comment:

  1. It is possible to compare the radiological consequences occurred in Chernobyl with those expected in Fukushima and elsewhere? If the discharge Fukushima is 10% of it was in Chernobyl,but dispersion models have different parameters that are other meteorological conditions.
    If the discharge to the sea has faded, it can also be thought transferebncia the plankton and fish and have bioaccumulation