Accident in the Japanese NPP Fukushima: Spread of Radioactivity/first source
estimates from CTBTO data show large source terms at the beginning of theaccident/weather currently not favourable/low level radioactivity meanwhile observed
over U.S. East Coast and Hawaii (Update: 22 March 2011 15:00)

Weather in the crisis region
The weather front that crossed the crisis region meanwhile went out. Rain in Fukushima and Tokyo stopped. The winds are weak,
mostly from northerly to easterly directions. Air from the reactors can thus be blown inland.
Tomorrow and the day after tomorrow, winds from westerly directions predominate. Air is thus mostly transported towards thePacific.
On Friday, a new disturbance is expected to cross the region. There is again potential transport of radioactivity inland.

First emission estimates
In the phase of March 12 to 13, the Fukushima emissions were mostly transported to the Pacific, eventually hitting the CTBTO
station in Sacramento/California. In the phase March 14 to 15, on the other hand, most of the emissions were transported inland,
hitting the CTBTO station in Takasaki, Japan. Based on simulated dilution factors and measurements, we were able to have a firstrough source estimate.
Regarding Iodine-131, the picture is relatively homogeneous. A source term of 10 17 Bq per day would explain the measurements inTakasaki as well as Sacramento. The total 4-day emission of 4 1017 Bq is on the order of 20% of the total emissions of Iodine-131
that occurred during the Chernobyl accident. Regarding Cesium-137, the situation is a bit different. In the cloud eventually
propagating to the United States, the ratio of Iodine-131 to Cesium-137 was about 30. This is similar to the Chernobyl accident. InTakasaki, however, this ratio was four. This would indicate a much larger Cesium-137 release in the second two-day period after
the accident. Taking this together, the source terms would be about 3 10 15 Bq during the first two days, and 3 1016 during thesecond two-day period. In sum, this could amount to about 50% of the Chernobyl source term of Cesium-137.

Dispersion Modeling
The results of the dispersion model show that radioactivity is transported inland today. Tomorrow, the cloud goues to the Pacific.
The day after tomorrow, the cloud is mostly transported to the Pacific Ocean, but inland regions north and south of the reactor may
be affected again.
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 UTCFigure: Spread of Radioactivity over Eastern Asia the day aftertomorrow 12:00 UTC

Radiation data/CTBTO
Currently, radiation data from CTBTO (last update today, data are from 19 March) show that low levels of radiations aremeanwhile observed in Hawaii, Wake Islands (Pacific) and the U.S. East Coast. The I-131 levels in Hawaii were on the order ofmBqm-3, the levels in Charlottesville, Virginia were close to the detection limit (µBqm-3). There is no health risk whatsoever.

Dr. Gerhard Wotawa
Division for Data, Methods and Modelling
Central Institute for Meteorology and Geodynamics
Hohe Warte 38, 1190 Wiengerhard.wotawa@zamg.ac.at

ZAMG 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