Note that the full report is presented as seven separate pdf files and can be found here:
Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Resulting from the triple meltdowns at the Fukushima-Daiichi Nuclear Power Plant there were significant releases of radionuclides to the atmosphere and directly to the ocean in March and April of 2011. Current estimates of the amount of 137-Cesium (137-Cs, half life 30.17 years) released from Fukushima to the atmosphere range from 9 to 37 PBq (PBq = 10^15 Bq) and 2.3 to 26.9 PBq directly to the coastal ocean (references in report). The uncertainties of these estimates in the individual studies cited in the report reflect sparse monitoring data during the early stages of the disaster owing to power loss, tsunami damage and errors in the respective models data inversion approaches.
To obtain better estimates of the 137-Cs source term (and associated radionuclides mobilized during the early stages of the disaster) the scientific team assembled by the Science Council of Japan compared the output of a suite of atmosphere and ocean models with existing observations made globally by the international scientific community.
The results of this intercomparison were as follows and are reported on pg. 50-51 of the study:
1. The study estimated the atmospheric release of 137-Cs of 19.4 +- 3.0 PBq through the end of March 2011 which is in between previous high and low estimates
2. Best estimates of direct ocean discharge of 137-Cs to the Pacific in addition to atmospheric deposition are 2.3 to 26.9 PBq and the panel could not determine which model provided the most robust estimate
3. About 19.5 +- 5% of releases were deposited to land while about 80% ended up in the Pacific Ocean
4. The distribution of 137-Cs in the ocean can't be reproduced without atmospheric deposition and direct ocean releases to the Pacific
These 137-Cs releases from Fukushima compare with the ~100 PBq released by the Chernobyl disaster in 1986.
Further, coordinated, international efforts are required to better constrain the source term as environmental impact assessments and mitigation measures would benefit from more accurate and precise determinations of Fukushima releases.
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