Inverse estimation of source parameters of oceanic radioactivity dispersion models associated with the Fukushima accident

Abstract

With combined use of the ocean–atmosphere simulation models and field observation data, we evaluate the parameters associated with the total caesium-137 amounts of the direct release into the ocean and atmospheric deposition over the western North Pacific caused by the accident of Fukushima Daiichi nuclear power plant (FNPP) that occurred in March 2011. The Green's function approach is adopted for the estimation of two parameters determining the total emission amounts for the period from 12 March to 6 May 2011. It is confirmed that the validity of the estimation depends on the simulation skill near FNPP. The total amount of the direct release is estimated as 5.5–5.9 × 10¹⁵ Bq, while that of the atmospheric deposition is estimated as 5.5–9.7 × 10¹⁵ Bq, which indicates broader range of the estimate than that of the direct release owing to uncertainty of the dispersion widely spread over the western North Pacific

Southward spreading of the Fukushima-derived radiocesium across the Kuroshio Extension in the North Pacific

“…The 2.4 PBq deposited onto the islands of Japan suggests that most of the remaining radiocesium, 6.4–35 PBq, found its way into the North Pacific through atmospheric deposition. Atmospheric models have estimated independently the total oceanic deposition to be 5.8–30 PBq5911122325, similar to the range of 6.4–35 PBq. However, the deposition on land has been overestimated in many of the models.…”

Fukushima and Ocean Radioactivity

“…These direct discharges peaked almost one month after the tsunami, in early April (Buesseler et al, 2011). 3.6 to 5.9 PBq (Kawamura et al, 2011;Estournel et al, 2012;Miyazawa et al, 2012;Tsumune et al, 2012). However, estimates of the source from analyses of (Table 1).…”

Cesium, iodine and tritium in NW Pacific waters – a comparison of the Fukushima impact with global fallout

“…Estournel et al (2012), using an inversion method based on measurements adjacent to the Fukushima NPP, estimated the 137 Cs direct release from 20 March to 30 June to be in the interval 4.1-4.5 PBq, adding 1 PBq to their estimation because the simulated results underestimated the 137 Cs activities measured offshore Fukushima. Miyazawa et al ( , 2013, using an inversion method based on 137 Cs data offshore Fukushima and numerical modeling, estimated the direct release of 137 Cs from 21 March to 30 April 2011 to be 5.5-5.9 PBq. Both the Estournel et al (2012) and Miyazawa et al (2013) estimations could be higher due to evaluating larger 137 Cs data sets (not only around the Fukushima Dai-ichi NPP, but also covering larger areas that could be influenced by the coastal current system).…”

“…Miyazawa et al ( , 2013, using an inversion method based on 137 Cs data offshore Fukushima and numerical modeling, estimated the direct release of 137 Cs from 21 March to 30 April 2011 to be 5.5-5.9 PBq. Both the Estournel et al (2012) and Miyazawa et al (2013) estimations could be higher due to evaluating larger 137 Cs data sets (not only around the Fukushima Dai-ichi NPP, but also covering larger areas that could be influenced by the coastal current system). Charette et al (2013), using a different approach based on Ra isotopes measured in seawater samples collected in June 2011 during the Ka'imikai-o-Kanaloa (KOK) cruise, which was carried out in the region 34-37 • N and 142-147 • E (Buesseler et a., 2012), estimated the 137 Cs source term due to direct liquid discharges to be 11-16 PBq.…”