Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations

Abstract

The source term of the atmospheric release of 131 I and 137 Cs due to the Fukushima Dai-ichi Nuclear Power Plant accident estimated by previous studies was validated and refined by coupling atmospheric and oceanic dispersion simulations with observed 134 Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for 134 Cs and 137 Cs, the sea surface concentration of 134 Cs was calculated using the previously estimated source term and was compared with measurement data. 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 × 10 17 and 1.3 × 10 16 Bq, respectively.

134Cs and 137Cs in the Seawater Around Japan and in the North Pacific

“…The eastward speed of the radioactive plume was estimated to be 8 cm s −1 . Moreover, atmospheric deposition of radioactive Cs and 131 I south of the KE near the east coast of Japan was strongly indicated by numerical simulations (Kawamura et al 2011 ;Kobayashi et al 2013 ). Thus, the highly radioactive Cs area observed in the central North Pacifi c in July 2011 and south of the KE near the east coast of Japan may have originated from atmospheric deposition.…”

“…In the present study, the radioactive Cs detected in the southern region was thought to contain the atmospheric fallout from the FNPP to the sea surface south of the KE during mid-March and early April 2011 (Sect. 2.3 ; Chino et al 2011 ;Rypina et al 2013 ;Honda et al 2012 ;Kobayashi et al 2013 ).…”

“…2.9d ). Then, the amount of 134 Cs in the core of the western part of the NPSTMW in September 2012 was estimated to be 1.07 PBq, which accounts for 7-47 % of the total amount of 134 Cs released directly into the ocean from the FNPP (2.3-14.8 PBq of 137 Cs; 134 Cs/ 137 Cs ratio assumed to be 1.0 Masumoto et al 2012 ), or 10 % of the total deposition including direct release and atmospheric surface deposition (11 PBq 134 Cs; Kobayashi et al 2013 ). Although the estimation includes enormous uncertainties, it should be noted that a considerable amount of the FNPP-derived radioactive Cs had been dispersed in the southwestern portion of the North Pacifi c across the KC, which was considered to act as a barrier against the southward dispersion of FNPP-derived radionuclides (Sect.…”

Marine radioecology after the Fukushima Dai-ichi nuclear accident: Are we better positioned to understand the impact of radionuclides in marine ecosystems?

“…Most efforts on the investigation of the contamination in the ocean have centred on the radiocaesium isotopes 134 Cs (T½ = 2.06 y) and 137 Cs (T½ = 30.2 y), of which between 5 to 11.7 PBq would have been deposited onto the regional ocean (Estournel et al, 2012;Kawamura et al, 2011;Kobayashi et al, 2013). The direct liquid discharges to sea were estimated to be about 2.8-5.9 PBq (Miyazawa et al, 2013;Tsumune et al, 2012;Tsumune et al, 2013), although other authors produced larger figures, ranging from 13.5 to 27 PBq (Bailly du Bois et al, 2012;Charette et al, 2013;Rypina et al, 2013).…”

Detection of 131I, 134Cs, and 137Cs Released into the Atmosphere from FNPP in Small Epipelagic Fishes, Japanese Sardine and Japanese Anchovy, off the Kanto Area, Japan

“…The total quantity of 131 I and 137 Cs released into the atmosphere between 12 March 2011 and 1 May 2011 was estimated to be approximately 2.0 × 10 17 Bq and 1.3 × 10 16 Bq, respectively. Furthermore, the quantities of 131 I and 137 Cs deposited on the ocean surface from the atmosphere were estimated as 9.9 × 10 16 Bq and 7.6 × 10 15 Bq, respectively (Kobayashi et al 2013 ).…”