Assessment of the amount of cesium‐137 released into the Pacific Ocean after the Fukushima accident and analysis of its dispersion in Japanese coastal waters

Estournel, Claude; Bosc, Emmanuel; Bocquet, Marc; Ulses, Caroline; Marsaleix, Patrick; Winiarek, Victor; Osvath, I.; Nguyen, Cong Tu; Duhaut, Thomas; Lyard, Florent; Michaud, Héloïse; Auclair, Francis

doi:10.1029/2012jc007933

Cited by 106 publications

(72 citation statements)

References 34 publications

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“…Using the numerical-model-based average age of 27 days, this value increases to 16 PBq. Our direct discharge estimated range is significantly greater (∼ 2-5 times) than an early (3.5 PBq, Tsunume et al, 2011) and more recent estimate of direct ocean release (5.1-5.5 PBq, Estournel et al, 2012), but generally consistent with the estimate (16.2 ± 1.6 PBq) obtained by Rypina et al (2013), and within the range of 12-41 PBq reported by Bailly du Bois et al (2012). The variability in total direct ocean discharges of Cs is due to the large uncertainties of the different transport and inversion processes used by each study and lack of spatially distributed observations in the surrounding region, which leads to uncertainty in the ocean inventory of Cs at any given point in time.…”

Section: Discussionmentioning

confidence: 84%

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

et al. 2013

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Radium has four naturally occurring isotopes that have proven useful in constraining water mass source, age, and mixing rates in the coastal and open ocean. In this study, we used radium isotopes to determine the fate and flux of runoff-derived cesium from the Fukushima Dai-ichi Nuclear Power Plant (FNPP). During a June 2011 cruise, the highest cesium (Cs) concentrations were found along the eastern shelf of northern Japan, from Fukushima south, to the edge of the Kuroshio Current, and in an eddy ~ 130 km from the FNPP site. Locations with the highest cesium also had some of the highest radium activities, suggesting much of the direct ocean discharges of Cs remained in the coastal zone 2–3 months after the accident. We used a short-lived Ra isotope (²²³Ra, t_1/2 = 11.4 d) to derive an average water mass age (T_r) in the coastal zone of 32 days. To ground-truth the Ra age model, we conducted a direct, station-by-station comparison of water mass ages with a numerical oceanographic model and found them to be in excellent agreement (model avg. T_r = 27 days). From these independent T_r values and the inventory of Cs within the water column at the time of our cruise, we were able to calculate an offshore ¹³⁴Cs flux of 3.9–4.6 × 10¹³ Bq d⁻¹. Radium-228 (t_1/2 = 5.75 yr) was used to derive a vertical eddy diffusivity (K_z) of 0.7 m² d⁻¹ (0.1 cm² s⁻¹); from this K_z and ¹³⁴Cs inventory, we estimated a ¹³⁴Cs flux across the pycnocline of 1.8 × 10⁴ Bq d⁻¹ for the same time period. On average, our results show that horizontal mixing loss of Cs from the coastal zone was ~ 10⁹ greater than vertical exchange below the surface mixed layer. Finally, a mixing/dilution model that utilized our Ra-based and oceanographic model water mass ages produced a direct ocean discharge of ¹³⁴Cs from the FNPP of 11–16 PBq at the time of the peak release in early April 2011. Our results can be used to calculate discharge of other water-soluble radionuclides that were released to the ocean directly from the Fukushima NPP

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Section: Discussionmentioning

confidence: 84%

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

et al. 2013

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“…In the days-weeks following the reactor meltdowns, dissolved 137 Cs activities reached >60 × 10 6 Bq·m −3 in the ocean closest to the FDNPP (5). Numerical modeling demonstrated that a net southward flowing coastal current transported this highly radioactive seawater along the shoreline (11). We hypothesize that seawater intrusion, driven in part by waves and tides (12)(13)(14)(15), led to the storage of 137 Cs by adsorption onto beach sands.…”

Section: Resultsmentioning

confidence: 99%

Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan

Sanial

Buesseler

Charette

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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There are 440 operational nuclear reactors in the world, with approximately one-half situated along the coastline. This includes the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), which experienced multiple reactor meltdowns in March 2011 followed by the release of radioactivity to the marine environment. While surface inputs to the ocean via atmospheric deposition and rivers are usually well monitored after a nuclear accident, no study has focused on subterranean pathways. During our study period, we found the highest cesium-137 (137Cs) levels (up to 23,000 Bq⋅m−3) outside of the FDNPP site not in the ocean, rivers, or potable groundwater, but in groundwater beneath sand beaches over tens of kilometers away from the FDNPP. Here, we present evidence of a previously unknown, ongoing source of Fukushima-derived 137Cs to the coastal ocean. We postulate that these beach sands were contaminated in 2011 through wave- and tide-driven exchange and sorption of highly radioactive Cs from seawater. Subsequent desorption of 137Cs and fluid exchange from the beach sands was quantified using naturally occurring radium isotopes. This estimated ocean 137Cs source (0.6 TBq⋅y−1) is of similar magnitude as the ongoing releases of 137Cs from the FDNPP site for 2013–2016, as well as the input of Fukushima-derived dissolved 137Cs via rivers. Although this ongoing source is not at present a public health issue for Japan, the release of Cs of this type and scale needs to be considered in nuclear power plant monitoring and scenarios involving future accidents.

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“…Over the last two years there have been a number of numerical modeling studies aimed at assessing the aftermath of the Fukushima disaster (e.g., Tsumane et al, 2011Tsumane et al, , 2013Kawamura et al, 2011;Estournel et al, 2012;Miyazawa et al, 2012;Masumoto et al, 2012;Bailly du Bois et al, 2012). Forward numerical models have allowed simulation of the spread of radioactive waters into the ocean.…”

Section: Modeling the Spreading Of 137 Csmentioning

confidence: 99%

Short-term dispersal of Fukushima-derived radionuclides off Japan: modeling efforts and model-data intercomparison

et al. 2013

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The Great East Japan Earthquake and tsunami that caused a loss of power at the Fukushima nuclear power plants (FNPP) resulted in emission of radioactive isotopes into the atmosphere and the ocean. In June of 2011, an international survey measuring a variety of radionuclide isotopes, including ¹³⁷Cs, was conducted in surface and subsurface waters off Japan. This paper presents the results of numerical simulations specifically aimed at interpreting these observations and investigating the spread of Fukushima-derived radionuclides off the coast of Japan and into the greater Pacific Ocean. Together, the simulations and observations allow us to study the dominant mechanisms governing this process, and to estimate the total amount of radionuclides in discharged coolant waters and atmospheric airborne radionuclide fallout. The numerical simulations are based on two different ocean circulation models, one inferred from AVISO altimetry and NCEP/NCAR reanalysis wind stress, and the second generated numerically by the NCOM model. Our simulations determine that > 95% of ¹³⁷Cs remaining in the water within ~600 km of Fukushima, Japan in mid-June 2011 was due to the direct oceanic discharge. The estimated strength of the oceanic source is 16.2 ± 1.6 PBq, based on minimizing the model-data mismatch. We cannot make an accurate estimate for the atmospheric source strength since most of the fallout cesium had left the survey area by mid-June. The model explained several key features of the observed ¹³⁷Cs distribution. First, the absence of ¹³⁷Cs at the southernmost stations is attributed to the Kuroshio Current acting as a transport barrier against the southward progression of ¹³⁷Cs. Second, the largest ¹³⁷Cs concentrations were associated with a semi-permanent eddy that entrained ¹³⁷Cs-rich waters, collecting and stirring them around the eddy perimeter. Finally, the intermediate ¹³⁷Cs concentrations at the westernmost stations are attributed to younger, and therefore less Cs-rich, coolant waters that continued to leak from the reactor in June of that year

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Assessment of the amount of cesium‐137 released into the Pacific Ocean after the Fukushima accident and analysis of its dispersion in Japanese coastal waters

Cited by 106 publications

References 34 publications

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan

Short-term dispersal of Fukushima-derived radionuclides off Japan: modeling efforts and model-data intercomparison

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