Estimation of marine source-term following Fukushima Dai-ichi accident

Abstract

Contamination of the marine environment following the accident in the Fukushima Dai-ichi nuclear power plant represented the most important artificial radioactive release flux into the sea ever known. The radioactive marine pollution came from atmospheric fallout onto the ocean, direct release of contaminated water from the plant and transport of radioactive pollution from leaching through contaminated soil. In the immediate vicinity of the plant (less than 500 m), the seawater concentrations reached 68,000 Bq.L(-1) for (134)Cs and (137)Cs, and exceeded 100,000 Bq.L(-1) for (131)I in early April. Due to the accidental context of the releases, it is difficult to estimate the total amount of radionuclides introduced into seawater from data obtained in the plant. An evaluation is proposed here, based on measurements performed in seawater for monitoring purposes. Quantities of (137)Cs in seawater in a 50-km area around the plant were calculated from interpolation of seawater measurements. The environmental halftime of seawater in this area is deduced from the time-evolution of these quantities. This halftime appeared constant at about 7 days for (137)Cs. These data allowed estimation of the amount of principal marine inputs and their evolution in time: a total of 27 PBq (12 PBq-41 PBq) of (137)Cs was estimated up to July 18. Even though this main release may be followed by residual inputs from the plant, river runoff and leakage from deposited sediments, it represents the principal source-term that must be accounted for future studies of the consequences of the accident on marine systems. The (137)Cs from Fukushima will remain detectable for several years throughout the North Pacific, and (137)Cs/(134)Cs ratio will be a tracer for future studies.

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

“…The Japanese government conducted intensive monitoring of 131 I, 134 Cs,and 137 Cs in the seawater offshore near the FNPP (Nuclear Regulation Authority 2014 ) and in fi sheries products from a wide area around Japan (Fisheries Agency 2014 ). Although information on radioactive contamination covering a broad area of the North Pacifi c is still quite limited (Aoyama et al 2013a , b ), some model experiments have addressed the dispersion of FNPP-derived radioactive Cs (Kawamura et al 2011 ;Bailly du Bois et al 2012 ;Dietze and Kriest 2012 ;Tsumune et al 2012 ;Miyazawa et al 2012 ), and estimated amounts of 137 Cs discharged directly into the ocean ranged from 2.3 to 14.8 PBq, with considerable uncertainties . Although most studies have discussed the surface dispersion patterns of FNPP-derived radioactive Cs, understanding the ocean distribution patterns of radioactive Cs throughout the water column is key to assessing its effects on marine ecosystems.…”

Decline in radiocesium in seafloor sediments off Fukushima and nearby prefectures

“…Another pathway by which 137 Cs can reach the monitoring area is atmospheric input. The inputs to the near-FDNPP oceanic area, including both direct release and atmospheric input, have been estimated to be 11-27 × 10 15 Bq, though the uncertainty is quite large owing to sparseness of the data set (Bailly du Bois et al 2012;Charette et al 2013;Rypina et al 2013). Therefore, the percentage of 137 Cs in the sediments relative to the total amount of 137 Cs transported to the monitoring area in September 2011 is probably substantially lower than 6.4%.…”

Evaluating the Probability of Catching Fat Greenlings (Hexagrammos otakii) Highly Contaminated with Radiocesium off the Coast of Fukushima

“…In April 2011, a concentration of 12,500 Bq/kg-wet and 14,400 Bq/kg-wet of radiocesium was detected in whole-fi sh specimens of Japanese sand lance ( Ammodytes personatus ) collected approximately 30 km south of the FNPP. These extremely high concentrations in coastal pelagic fi sh species were caused from their direct exposure to highly contaminated seawater (Bailly et al 2012 ;Oikawa et al 2013 ). It is known that cesium absorbed by marine organisms is excreted by their potassium ion transport system during osmoregulation (Furukawa et al 2012 ;Kaneko et al 2013 ).…”