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Publicatie Laka-bibliotheek:
Xenon-133 and Cesium-137 releases into the atmosphere from the Fukushima Daiichi nuclear power plant: determination of the source term, atmospheric dispersion and disposition (2011)

Auteur	A.Stohl, P.Seibert, G.Wotawa, D.Arnold, J.F.Burkhart, S.Eckhardt, C.Tapia, A.Vargas, T.J.Yasunari
	-
Datum	oktober 2011
Classificatie	4.21.8.60/07 (JAPAN - FUKUSHIMA (Dai’ichi ongeluk))
Voorkant

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.

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 (FD-NPP) developed 
into a disaster causing massive release of radioactivity into the atmosphere. In this 
study, we determine the emissions 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 
the first guess 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 16.7 (uncertainty range 13.4–20.0) EBq, which is the largest radioactive 
noble gas release in history not associated with nuclear bomb testing. There is strong 
evidence that the first strong 133Xe release started very early, possibly immediately 
after the earthquake and the emergency shutdown on 11 March at 06:00UTC. The 
entire noble gas inventory of reactor units 1–3 was set free into the atmosphere 
between 11 and 15 March 2011. For 137Cs, the inversion results give a total 
emission of 35.8 (23.3–50.1) PBq, or about 42% 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 exactly when spraying of water on the spent-fuel pool of unit 4 started. 
This indicates that emissions were not only coming from the damaged reactor cores, 
but also from the spent-fuel pool of unit 4 and confirms that the spraying was an 
effective countermeasure.

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