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 (<sup>133</sup>Xe) and the aerosol-bound caesium-137 (<sup>137</sup>Cs), 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 <sup>137</sup>Cs, measurements of bulk deposition. Regarding <sup>133</sup>Xe, 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 <sup>133</sup>Xe release started very early, possibly immediately after the earthquake and the emergency shutdown on 11 March at 06:00 UTC. The entire noble gas inventory of reactor units 1–3 was set free into the atmosphere between 11 and 15 March 2011. For <sup>137</sup>Cs, 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 <sup>137</sup>Cs 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. We also 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 <sup>137</sup>Cs 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 <sup>137</sup>Cs on land surfaces. The plume was also dispersed quickly over the entire Northern Hemisphere, first reaching North America on 1...

Fukushima-derived radiocesium in the northwestern Pacific Ocean in February 2012

“…Estimates of the total amount 137 Cs (or 134 Cs) released from the FNPP1 range widely from 7 (Chino et al, 2011) to 35 PBq (Stohl et al, 2011), of which a large portion released to the marine environment is also uncertain. Fukushima-derived 137 Cs has been transferred to the Pacific Ocean both through atmospheric deposition and direct discharge of contaminated waters.…”

Comparison of radioactive cesium contamination of lake water, bottom sediment, plankton, and freshwater fish among lakes of Fukushima Prefecture, Japan after the Fukushima fallout

“…Radiocesium was one of the major radioactive components in the fallout from the FNPP; the quantities of 137 Cs released into the atmosphere between 12 March and 1 May 2011 and deposited on the land and ocean surfaces were estimated as 5.8 × 10 15 and 7.6 × 10 15 Bq, respectively [2]. Further, Stohl et al [3] reported that, before 20 April 2011, 18 and 1.9 % of the total fallout was deposited on Japanese and other land areas, respectively. An aerial survey on 1 November 2011 showed that an area of about 8400 km 2 was contaminated with 134 Cs and 137 Cs at levels greater than 60 kBq/m 2 [4].…”

Analysis of a Nuclear Accident: Fission and Activation Product Releases from the Fukushima Daiichi Nuclear Facility as Remote Indicators of Source Identification, Extent of Release, and State of Damaged Spent Nuclear Fuel

“…It has been suggested, for instance, that the explosion at the Unit 4 cooling pool, which is not contained within any primary containment system, may have damaged fuel and contributed to or even composed the major source of the release of radionuclides to the environment (4)(5). This was based upon a correlation in time observed between the application of water over the spent fuel pool and a decrease in the atmospheric plume measured over Europe.…”