Accident in the Japanese NPP Fukushima: Spread of Radioactivity/ weather currently
not favourable (Update: 25 March 2011 16:00)

Weather in the crisis region
Currently, a disturbance is crossing the crisis region. There are numerous showers passing by. In Fukushima, we expect some rain
and possibly some snow overnight. There is rain also expected for Tokyo. Currently, weak easterly winds predominate, whichmeans that transport of radioactivity is slow. In the course of the night, the winds turn quickly to the west.
Tomorrow and the day after tomorrow, north-westerly winds predominate. Air from Fukushima will thus be transported to thePacific.

Emission estimates based on CTBTO data
Due to the numerous highly accurate radionuclide data (24-hour air samples) available to us from the world-wide network of theComprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna, we have been able to estimate the source strengths ofIodine-131 and Cesium-137 for the first few days of the accident. These estimates are subject to uncertainties, but they are accurateby the order of magnitude. Based on our current best estimate, we assume a daily emission of Iodine-131 of about 10 17 Bq, and adaily emission of Cesium-137 between 5 1015 und 5 1016 Bq. Calculated across the full accident scenario, one would assume asimilar source term of both isotopes as during the accident in Chernobyl.
Since the volatile gases and particles like Iodine-131 and Cesium-137 do only make up a certain proportion of the total effective
dose rates, our estimate does not imply that the effective dose rates around the Fukushima plant are comparable with thosemeasured around Chernobyl. Using only the volatile substances Iodine-131 and Cesium-137 to calculate the effective dose rates,
we end up with estimates that do not contradict the measurements provided by the Japanese Authorities and IAEA.

Dispersion Modeling
The results of the dispersion model show that radioactivity is transported a limited distance inland today. Tokyo and surroundings
seem to be not affected. Tomorrow and the day after tomorrow, the cloud is transported to the Pacific Ocean, as was the case mostof the time during the last two weeks (see figures below).
The colour scale shows a total of 5 colours. The area marked „E“shows an area with estimated current equivalent dose rate of 10mSv/h (in a 25x25 km2 square). The violet colour on the outer edge of contaminated areas (Area A) represents 0,3 µSv/h, whichcorresponds to the amount of the natural background radiation dose.

Figure: Spread of Radioactivity over Eastern Asia today and tomorrow 12:00 UTC

Figure: Spread of Radioactivity over Eastern Asia the day aftertomorrow 12:00 UTCDr. Gerhard Wotawa
Division for Data, Methods and Modelling
Central Institute for Meteorology and Geodynamics
Hohe Warte 38, 1190 Wien
gerhard.wotawa@zamg.ac.atZAMG will not answer any questions related to travel in Japan or in other parts of the world, since this is the responsibility of nationalradiation protection authorities. Travel advisories and warnings are available from your foreign ministry. In Austria, such advisories areavailable on www.bmeia.gv.at.

This information is updated daily, and whenever the development of the situation requires it.

Videos:Plume spread from Fukushima/Permanent Release/Iodine-131