Accident in the Japanese NPP Fukushima: Spread of Radioactivity / Weather today
not favourable/ by comparison with CTBTO radioactivity data, ZAMG estimates highemissions of Iodine and Caesium during the first accident week / Measurements show
Hemispheric-scale spread of radioactivity (Update: 1. April 2011 12:00)

Weather in the crisis region
Until Sunday, the crisis region is under the influence of a north-westerly circulation. Disturbances are passing the region.
Nevertheless, it stays dry most of the time.
Today, a cold front is passing by, without much rain. The surface wind currently comes from the south, meaning that radioactivity
could be transported to inland areas north of the reactor. By 2100 UTC, the wind will shift to westerly direction, transporting
material mainly to the Pacific.
On Saturday, a surface low is forming on the lee side of the mountain range. This low pressure system will trigger northerly tonorth-easterly winds in the Tokyo region, but mainly westerly to northerly winds at the accident location. There may be a few rain
showers.
On Saturday, the region comes under the influence of a high-pressure system. Winds come mostly from north-westerly to northerlydirections. The weather is cool but dry.

The reference time for this weather forecast is Coordinated Universal Time (UTC); please mind the time difference of plus 9 hours
between UTC and the local time in Japan

Dispersion ModelingAccording to our dispersion model forecast, a potential radioactive cloud could be transported to inland areas north of the reactor
today. Tomorrow and on Sunday, the dominating north-westerly circulation will transport radiation towards the Pacific. An
unfavourable influence of unresolved local wind systems can, however, not be excluded for tomorrow, depending on the exact
position and strength of the surface low.

The colour scale shows a total of five colours. „Area A“ (violet) is meant to mark an area with maximum dose rate of 0,3 µSv/h,
which corresponds to the amount of the natural background radiation dose. “Area B” (blue) marks a region with 3 Micro-Sievert
per hour. Finally, one arrives in ”Area E” with a maximum dose rate of 3 Milli-Sievert per hour. This dose rate is currently
certainly not exceeded in the regional area (25x25 km 2 box) around the NPP. Irrespective of the assumed emissions, the maximum
value of the model is always used to determine “Area E”. In case the situation around the NPP is changing to the worse, the scale
would be adapted.

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 UTC

Emission estimates based on CTBTO data
ZAMG published emission estimates of Iodine-131 and Cesium-137 from Fukushima during the first 3 days of the accident (March12-14). These amounted to 1017 Bq per day for Iodine-131 and between 5 1015 and 5 1016 Bq per day for Cesium-137. Related toIodine-131, one needs to take into account that CTBTO only measures a part of the total material, namely the Iodine-131 particles.
The gas is not sampled within the filter.
The CTBTO measurement network is not dense, and thus it takes, on the average, about 6 days before the first station is reached.
During transport, material is deposited and washed out, a process that is subject to significant uncertainties. Only during a few
days, material was directly transported from the reactor towards the CTBTO station Takasaki in Japan. During the first week, thishappened only once, namely on 15 March. The material sampled there was released late on 14 March (UTC), which was the periodwith the maximum emissions according to IAEA assessments.

The total uncertainty of the emissions can be estimated as follows:-Upper emission limit: Estimate of the source strength by modelling that takes into account washout and deposition.

-Lower emission limit: Estimate of the source strength by modelling passive tracer transport

The total uncertainty is estimated as follows:-If the cloud is directly measured in Takasaki: Factor 10-

If the cloud is measured after 6 days in California/Hawai/Alaska or the Philippines: Factor 1000

The estimate of the emission during the first week can thus be performed as follows:
March 14

Iodine-131 1016 to 1017 Bq/day
Caesium-137 1015 to 1016 Bq/day

March 12-13 and 15-19
Iodine-131 1014 to 1017 Bq/day
Caesium-137 1013 to 1016 Bq/day

Based on this estimate, the sum of Iodine-131 emitted during the first week in Fukushima is between 1016 and 7 1017 Bq. The
sum of Caesium-137 is between 10 15 and 7 1016 Bq. Since Iodine and Caesium particles are no passive tracers, the lower
emission limits are estimated conservatively.

Radioactivity Measurements
The global radionuclide measurements performed in the framework of the Comprehensive Nuclear-Test-Ban Treaty (CTBT)
currently show that traces of Iodine and Caesium can be found over most parts of the Northern Hemisphere (status ofmeasurements: 1 April, data are from 29 March). Regarding Europe, the CTBTO stations in Freiburg/Germany andStockholm/Sweden measured Iodine-131 activity concentrations of 250 and 1700 µBqm-3, respectively. Similar values werereported from there yesterday. The currently measured nuclides were emitted in Fukushima two weeks ago.

Dr. Gerhard Wotawa
Stabsstelle Daten/Methoden/ModelleZentralanstalt für Meteorologie und Geodynamik
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