The Journal of Nuclear Science and Technology Volume 50, Issue 3, 2013 contains a paper titled Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations. Using the best available data and models it provides new estimates for the total quantity of I-131 and Cs-137 that was released into the atmosphere by the events at Fukushima Dai-ichi during the period from March 12 – March 20, 2013.

The release rate of 137-Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of 131-I was refined to follow the radioactivity ratio of 137-Cs. As a result, the total amounts of 131-I and 137-Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.0 E17 and 1.3 E16 Bq, respectively.

In a post published in November 2011, I challenged the use of the word “spew” in relation to the radioactive material discharged into the atmosphere by converting a published number of becquerels into the more useful quantity of grams or kilograms. Since that computation was based on a different estimated number of becquerels, I decided to update the computation.

For I-131 – 2.0 E17 Bq = 5.4 million curies. Each curie of 1-31 weighs just 0.000008 grams.
Therefore the total amount of I-131 released into the atmosphere was:

5,400,000 curies x 0.000008 grams I-131/curie = 43.2 grams I-131

(Note: the number used previously was 6.3 E17 Bq or 17 million curies which I calculated was 136 grams.)

For Cs-137 – 1.3 E16 Bq = 350,000 curies. Cs-137 has a much longer half life than I-131; each gram only contains about 88 curies (0.0114 grams Cs-137/curie)

Therefore the total mass of Cs-137 released into the atmosphere was”

350,000 curies x 0.0114 gram Cs-137/curie = 3980 grams (4 kg) – of Cs-137.

(Note: I made some poor assumptions in November 2011; I could not find any specific numbers for Cs-137. Based on those poor assumptions, my previous calculation indicated 97 kilograms of Cs-137, so this is a considerably lowered estimate.)

Neither of those mass numbers seem like they qualify for the frequently used descriptor of “spewing”. I hope that knowing those numbers helps people to understand how lightly contaminated the area around the Fukushima nuclear power plant is and why I think it is a travesty that people are still being forcibly separated from their homes.

As always, I appreciate any efforts to check my math to make sure I did not drop or add a key zero or move a decimal point.