Stohl et. al. Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant….

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Quote from Stohl et al:

Atmos. Chem. Phys., 12, 2313–2343, 2012
© Author(s) 2012. CC Attribution 3.0 License.

Xenon-133 and caesium-137 releases into the atmosphere from the
Fukushima Dai-ichi nuclear power plant: determination of the
source term, atmospheric dispersion, and deposition
A. Stohl1, P. Seibert2, G. Wotawa3, D. Arnold2,4, J. F. Burkhart1, S. Eckhardt1, C. Tapia5, A. Vargas4, and
T. J. Yasunari6
1NILU – Norwegian Institute for Air Research, Kjeller, Norway
2Institute of Meteorology, University of Natural Resources and Life Sciences, Vienna, Austria
3Central Institute for Meteorology and Geodynamics, Vienna, Austria
4Institute of Energy Technologies (INTE), Technical University of Catalonia (UPC), Barcelona, Spain
5Department of Physics and Nucelar Engineering (FEN),Technical University of Catalonia (UPC), Barcelona, Spain
6Universities Space Research Association, Goddard Earth Sciences and Technology and Research, Columbia,
MD 21044, USA
Correspondence to: A. Stohl (
Received: 8 October 2011 – Published in Atmos. Chem. Phys. Discuss.: 20 October 2011
Revised: 1 February 2012 – Accepted: 23 February 2012 – Published: 1 March 2012

Abstract. On 11 March 2011, an earthquake occurred about
130 km off the Pacific coast of Japan’s main island Honshu,
followed by a large tsunami. The resulting loss of electric
power at the Fukushima Dai-ichi nuclear power plant developed
into a disaster causing massive release of radioactivity
into the atmosphere. In this study, we determine the
emissions into the atmosphere of two isotopes, the noble
gas xenon-133 (133Xe) and the aerosol-bound caesium-137
(137Cs), which have very different release characteristics as
well as behavior in the atmosphere. To determine radionuclide
emissions as a function of height and time until 20
April, we made a first guess of release rates based on fuel
inventories and documented accident events at the site. This
first guess was subsequently improved by inverse modeling,
which combined it with the results of an atmospheric transport
model, FLEXPART, and measurement data from several
dozen stations in Japan, North America and other regions.
We used both atmospheric activity concentration measurements
as well as, for 137Cs, measurements of bulk deposition.
Regarding 133Xe, we find a total release of 15.3 (uncertainty
range 12.2–18.3) EBq, which is more than twice as
high as the total release from Chernobyl and likely the largest
radioactive noble gas release in history. The entire noble gas
inventory of reactor units 1–3 was set free into the atmosphere
between 11 and 15 March 2011. In fact, our release
estimate is higher than the entire estimated 133Xe inventory
of the Fukushima Dai-ichi nuclear power plant, which we
explain with the decay of iodine-133 (half-life of 20.8 h) into
133Xe. There is strong evidence that the 133Xe release started
before the first active venting was made, possibly indicating
structural damage to reactor components and/or leaks due to
overpressure which would have allowed early release of noble
gases. For 137Cs, the inversion results give a total emission
of 36.6 (20.1–53.1) PBq, or about 43% of the estimated
Chernobyl emission. Our results indicate that 137Cs emissions
peaked on 14–15 March but were generally high from
12 until 19 March, when they suddenly dropped by orders of
magnitude at the time when spraying of water on the spentfuel
pool of unit 4 started. This indicates that emissions may
not have originated only from the damaged reactor cores, but
also from the spent-fuel pool of unit 4. This would also confirm
that the spraying was an effective countermeasure. We
explore the main dispersion and deposition patterns of the radioactive
cloud, both regionally for Japan as well as for the
entire Northern Hemisphere. While at first sight it seemed
fortunate that westerly winds prevailed most of the time during
the accident, a different picture emerges from our detailed
analysis. Exactly during and following the period of
the strongest 137Cs emissions on 14 and 15 March as well
as after another period with strong emissions on 19 March,
the radioactive plume was advected over Eastern Honshu Island,
where precipitation deposited a large fraction of 137Cs
on land surfaces. Radioactive clouds reached North America
on 15 March and Europe on 22 March. By middle of
April, 133Xe was fairly uniformly distributed in the middle
latitudes of the entire Northern Hemisphere and was for the
first time also measured in the Southern Hemisphere (Darwin
station, Australia). In general, simulated and observed
concentrations of 133Xe and 137Cs both at Japanese as well
as at remote sites were in good quantitative agreement. Altogether,
we estimate that 6.4 PBq of 137Cs, or 18% of the total
fallout until 20 April, were deposited over Japanese land areas,
while most of the rest fell over the North Pacific Ocean.
Only 0.7 PBq, or 1.9% of the total fallout were deposited on
land areas other than Japan.

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