.The Austrian "Zentralanstalt für Meteorologie und Geodynamik (ZAMG) (the official meteorological and geophysical service of Austria), has produced an analysis estimating the total emissions of Iodine-131 and Cesium-137 since the beginning of the crisis at Fukushima Daiichi, finding them of the same order of magnitude as the emissions at Chernobyl. The radiation load is measured in Becquerels (Bq). Each Bq is the disintegration of a single atomic nucleus, so the values become quite large. They are expressed in scientific notation.
"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 first rough source estimate.
"Regarding Iodine-131, the picture is relatively homogeneous. A source term [total release] of 1017 Bq per day would explain the measurements in Takasaki as well as Sacramento. The total 4-day emission of 4x1017 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. In Takasaki, 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 term [total release] would be about 3x1015 Bq during the first two days, and 3x1016 during the second two-day period. In sum, this could amount to about 50% of the Chernobyl source term of Cesium-137.
For more, click here for the English pdf download.
So far, I believe Japan has been very lucky that the winds have been primarily out to sea (toward the east). I also note that their evacuation/shelter zone is the exact same size as the one that was initially specified for Chernobyl: 30 km (approx. 19 miles). However, the American government has advised their citizens to evacuate out to 50 miles from the plant. The outskirts of Tokyo are only 130 miles away, with fairly large population centers in the 100 mile range.
It is important to note that the total quantity of fuel involved in the Fukushima Daiichi disaster is much more than that at Chernobyl -- perhaps by a factor of 30 times. There are at least 3 fueled reactors with very serious damage, and an exceptionally large amount of fuel was being stored in each of the spent fuel pools. Plus some concern exists about the fifth and sixth reactors and pools.
This is still an exceptionally serious situation.