GI2.2 | Geoscience problems related to radioactive contamination originated from nuclear power plants and other human activities: Chernobyl, Fukushima, and Zaporizhzhia

GI2.2

EDI

The session gathers multi-disciplinary geoscientific aspects such as dynamics, reactions, and environmental/health consequences of radioactive materials that are massively released accidentally (e.g., Chernobyl and Fukushima nuclear power plant accidents, wide fires, etc.), future potential risk of leakage (e.g., Zaporizhzhia nuclear power plant) and by other human activities (e.g., nuclear tests).

The radioactive materials are known as polluting materials that are hazardous for human society, but are also ideal markers in understanding dynamics and physical/chemical/biological reactions chains in the environment. Therefore, man-made radioactive contamination involves regional and global transport and local reactions of radioactive materials through atmosphere, soil and water system, ocean, and organic and ecosystem, and its relations with human and non-human biota. The topic also involves hazard prediction, risk assessment, nowcast, and countermeasures, , which is now urgent important for the nuclear power plants in Ukraine.

By combining long monitoring data (> halftime of Cesium 137 after the Chernobyl Accident in 1986, 12 years after the Fukushima Accident in 2011, and other events), we can improve our knowledgebase on the environmental behavior of radioactive materials and its environmental/biological impact. This should lead to improved monitoring systems in the future including emergency response systems, acute sampling/measurement methodology, and remediation schemes for any future nuclear accidents.

The following specific topics have traditionally been discussed:
(a) Atmospheric Science (emissions, transport, deposition, pollution);
(b) Hydrology (transport in surface and ground water system, soil-water interactions);
(c) Oceanology (transport, bio-system interaction);
(d) Soil System (transport, chemical interaction, transfer to organic system);
(e) Forestry;
(f) Natural Hazards (warning systems, health risk assessments, geophysical variability);
(g) Measurement Techniques (instrumentation, multipoint data measurements);
(h) Ecosystems (migration/decay of radionuclides).

The session consists of updated observations, new theoretical developments including simulations, and improved methods or tools which could improve observation and prediction capabilities during eventual future nuclear emergencies. New evaluations of existing tools, past nuclear contamination events and other data sets also welcome.

Co-organized by BG8/ERE1/ESSI1/GM11/NH8/OS2
Convener: Daisuke Tsumune | Co-conveners: Hikaru SatoECSECS, Liudmila KolmykovaECSECS, Masatoshi Yamauchi
Orals
| Wed, 26 Apr, 16:15–18:00 (CEST)
 
Room G2
Posters on site
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
Hall X4
Posters virtual
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
vHall ESSI/GI/NP
Orals |
Wed, 16:15
Wed, 10:45
Wed, 10:45

Orals: Wed, 26 Apr | Room G2

Chairpersons: Daisuke Tsumune, Masatoshi Yamauchi, Hikaru Sato
16:15–16:20
16:20–16:30
|
EGU23-4152
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GI2.2
|
ECS
|
On-site presentation
Shuhan Zhuang, Xinwen Dong, Yuhan Xu, and Sheng Fang

Wet scavenging modeling remains a challenge of the atmospheric transport of 137Cs following the Fukushima Daiichi Nuclear Power Plant accident, which significantly influences the detailed spatiotemporal 137Cs distribution. Till now, numerous wet deposition schemes have been proposed for 137Cs, but it is often difficult to evaluate them consistently, due to the limited resolution of meteorological field data and detailed differences in model implementations. This study evaluated the detailed behavior of 25 combinations of in- and below-cloud wet scavenging models in the framework of the Weather Research and Forecasting-Chemistry model, using high-resolution (1 km × 1 km) meteorological input. The above implementation enables consistent evaluation with great details, revealing complex local behaviors of these combinations. The 1-km-resolution simulations were compared with simulations obtained previously using 3-km-resolution meteorological field data, with respect to the rainfall pattern of the east Japan during the accident, atmospheric concentrations acquired at the regional SPM monitoring sites and the total ground deposition. The capability of these models in reproducing local-scale observations were also investigated with a local-scale observations at the Naraha site, which his only 17.5 km from the Fukushima Daiichi Nuclear Power Plant. The performance of the ensemble mean was also evaluated. Results revealed that the 1-km simulations better reproduce the cumulative rainfall pattern during the Fukushima accident than those revealed by the 3-km simulations, but showing with spatiotemporal variability in accuracy. And rainfall below 1 mm/h is critical for the simulation accuracy. Those single-parameter wet deposition models that rely solely on the rainfall showed improvements in performance in the 1-km simulations relative to that in the 3-km simulations, because of the improved rainfall simulation in the 1-km results. Those multiparameter models that rely on both cloud and rainfall showed more robust performance in both the 3-km and -1km simulations, and the Roselle–Mircea model presented the best performance among the 25 models considered. Besides rainfall, wind transport showed substantial influence on the removal process of atmospheric 137Cs, and it was nonnegligible even during periods in which wet deposition was dominant. The ensemble mean of the 1-km simulations better reproduces the high deposition area and the total deposition amount is closer to the observations than the 3-km simulation. At the local scale, the 1-km-resolution simulations effectively reproduced the 137Cs concentrations observed at the Naraha site, but with deviations in peak timing, mainly because of biased wind direction. These findings indicate the necessity of a multi-parameter model for robust regional-scale wet deposition simulation and a refined wind and dispersion model for local-scale simulation of 137Cs concentration.

How to cite: Zhuang, S., Dong, X., Xu, Y., and Fang, S.: Modeling and sensitivity study of wet scavenging models for the Fukushima accident using 1-km-resolution meteorological field data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4152, https://doi.org/10.5194/egusphere-egu23-4152, 2023.

16:30–16:40
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EGU23-13366
|
GI2.2
|
On-site presentation
Kentaro Akasaki, Shu Mori, Eiichi Suetomi, and Yuko Hatano

We compare the atmospheric concentrations of Cs-137 after a decade between Chernobyl and Fukushima cases. We plotted 8 datasets on log-log axes (5 cases in Chernobyl and 3 cases Fukushima) and found that they appear to follow a single function.

There have been measured the atmospheric concentration after the Chernobyl accident for more than 30 years [1]. On the other hand, several teams of Japanese researchers have been measured in Fukushima and its vicinity for almost 10 years. [2][3] In this study, we compare 5 sites in Chernobyl (Pripyat, Chernobyl, Baryshevka, Kiev, and Polesskoe) and 3 sites in Fukushima (FDNPP O-6 and O-7, Univ. Fukushima).

We adjust the magnitude of the data because it depends on the amount of the initial deposition. After the adjustment, we plot the 8 cases on a log-log plot. We found that the 8 cases collapse together, with the power index of -1.6. Namely,

C(t) ~ t^{-1.6}.               …(1)

Incidentally, we have been proposed a formula which reproduce the long-term behavior of atmospheric concentration at a fixed location as

C(t) = A exp(-bt) t^{-4/3}    …(2)

where A is a parameter which relates to the amount of the initial deposition and b as the reaction rate of all the first-order reactions (including the radioactive decay rate, the vegetation uptake rate, the runoff rate, etc). We will investigate the difference in the power-law index in Eq. (1) and (2). The parameter b is highly dependent on the environment. When we take a proper value of b, the apparent decrease of the concentration will change from t^{-4/3}. We may make the apparent power-index close to -1.6.

 

[1] E. K. Garger, et al., J. Env. Radioact., 110 (2012) 53-58.

[2] A. Watanabe, et al., Atmos. Chem. Phys. 22 (2022) 675-692.

[3] T. Abe, K. Yoshimura, Y. Sanada, Aerosol and Air Quality Research, 21 (2021) 200636.

How to cite: Akasaki, K., Mori, S., Suetomi, E., and Hatano, Y.: Similarity of long-term temporal decrease in atmospheric Cs-137 between Chernobyl and Fukushima, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13366, https://doi.org/10.5194/egusphere-egu23-13366, 2023.

16:40–16:50
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EGU23-6026
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GI2.2
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On-site presentation
Yuichi Onda, Taichi Kawano, Keisuke Taniguchi, and Junko Takahashi

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 resulted in the release of large amounts of radioactive cesium-137 (137Cs) into the environment. It is important to characterize the Cs-137 dynamics throughout the river from the headwaters to the downstream. Previous studies have suggested the importance of dissolved forms of Cs-137 in organic matter in small watersheds and dissolved forms in suspended solids in large watersheds. Since the concentration of suspended-form Cs has been shown to decrease significantly after decontamination in evacuated areas (Feng et al. 2022), this rapid decrease in suspended-form Cs-137 concentration can be used to determine the cause of dissolved-form Cs. Therefore, we attempted to evaluate whether the dissolved Cs-137 was derived from organic matter or suspended solids by comparing data before and after decontamination.

 The objective of this study is to compare the decreasing trends of Cs-137 concentrations in decontaminated and undecontaminated areas based on long-term monitoring of suspended solids, dissolved solids, and coarse organic matter Cs-137 concentrations since 2011. The study area includes four headwater basins and four river basins (eight sites in total) in the Kuchibuto River watershed in the Yamakiya district of Fukushima Prefecture, located approximately 35 km northwest of the FDNPP.

In the Kuchibuto River watershed, a large inflow of decontaminated soil with low Cs-137 concentrations due to an increase in the amount of bare land caused by decontamination resulted in a rapid decrease in the concentration of suspended-form 137Cs in the decontaminated area in the headwaters and in the upper reaches of the river. However, no clear effect of decontamination was observed in the concentrations of dissolved Cs-137 and Cs-137 in coarse organic matter. Comparison of the slopes of Cs-137 concentrations in the suspended, dissolved, and coarse organic matter showed that the slope of the dissolved form was similar to that of the coarse organic matter in the source watersheds, and similar to that of the SS in the downstream watersheds. These results suggest that the contribution of dissolved Cs-137 from organic matter in small watersheds and that from suspended solids in large watersheds is significant.

How to cite: Onda, Y., Kawano, T., Taniguchi, K., and Takahashi, J.: Dynamic change of dissolved Cs-137 from headwaters to downstream in the Kuchibuto River catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6026, https://doi.org/10.5194/egusphere-egu23-6026, 2023.

16:50–17:00
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EGU23-1081
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GI2.2
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On-site presentation
Alexei Konoplev

In the wake of Chernobyl and Fukushima accidents radiocesium has become a radionuclide of most environmental concern. The ease with which this radionuclide moves through the environment and is taken up by plants and animals is governed by its chemical forms and site-specific environmental characteristics. Distinctions in climate and geomorphology, as well as 137Cs speciation in the fallout result in differences in migration rates of 137Cs in the environment and rates of its natural attenuation. In Fukushima areas 137Cs was found to be strongly bound to soil and sediment particles, its bioavailability being reduced as a result.  Up to 80% of the deposited 137Cs on the soil were reported to be incorporated in hot glassy particles (CsMPs) insoluble in water. Disintegration of these particles in the environment is much slower than of Chernobyl-derived fuel particles. The higher annual precipitation and steep slopes in Fukushima contaminated areas are conducive to higher erosion and higher total radiocesium wash-off. Typhoons Etou in 2015 and Hagibis in 2019 demonstrated the pronounced redistribution of 137Cs on river watersheds and floodplains, and in some cases natural self-decontamination occurred. Among the common features in 137Cs behavior in Chernobyl and Fukushima is a slow decrease in 137Cs activity concentration in small, closed, and semi-closed lakes and its particular seasonal variations: increase in summer and decrease in winter.

How to cite: Konoplev, A.: Fukushima and Chernobyl: similarities and differences of radiocesium behavior in the soil-water environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1081, https://doi.org/10.5194/egusphere-egu23-1081, 2023.

17:00–17:10
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EGU23-12670
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GI2.2
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ECS
|
On-site presentation
Floris Abrams, Lieve Sweeck, Johan Camps, Grethell Castillo-Reyes, Bin Feng, Yuichi Onda, and Jos Van Orshoven

Government-led decontamination of agricultural land in the Fukushima accident (2011) region has lowered the on-site radiation risk considerably. From 2013 to early 2017, 11.9% of the land in the Fukushima disaster affected Niida watershed in Japan was remediated through topsoil removal. However, this resulted in a 237.1% increase in suspended sediment loads in the river for 2016 compared to 2013.  In contrast, sediment loads decreased by 41% from 2016 to 2017; this can be attributed to the effect of natural vegetation restoration on sediment yield and transfer patterns (Bin et al., 2022). Since radiocaesium firmly binds to the clay minerals in the soil, it is inevitably transported along with the sediments downstream to the river systems. These observations confirm that rapid, spatially targeted interventions, such as revegetation, e.g., through afforestation, have the potential to decrease the magnitude and period of increased exports of contaminated sediments. The CAMF tool (Cellular Automata-based Heuristic for Minimizing Flow) (Vanegas et al., 2012) was originally designed to find the cells in a raster representation of a watershed for which afforestation would lead to a maximal reduction of sediment exports with minimal effort or cost while taking sediment flow from cell to cell into account. In our research, we adapted the CAMF tool to account for the radiocaesium budgets associated with the transported sediments. We applied the approach to the Niida catchment, where land-cover changes in upstream decontaminated regions are detected using drone imagery and linked to increased sediment loads in the Niida river using long-term river monitoring systems. For example In 2014, agricultural land (18.02 km2) was one of the major land uses in the regions where decontamination was ordered, resulting in increased sediment loads from 2014 to 2016. By recognizing both the on- and off-site impacts of the remediation interventions and their temporal dynamics, the modified CAMF tool offers scope for supporting the formulation of spatio-temporal schemes for the remediation of agricultural land. These schemes aim to decrease the radiation risk for downstream communities and minimize the potential recontamination of already decontaminated sites.

How to cite: Abrams, F., Sweeck, L., Camps, J., Castillo-Reyes, G., Feng, B., Onda, Y., and Van Orshoven, J.: Minimizing the loss of radioactively contaminated sediment from the Niida watershed (Fukushima, Japan) through spatially targeted afforestation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12670, https://doi.org/10.5194/egusphere-egu23-12670, 2023.

17:10–17:20
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EGU23-4697
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GI2.2
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ECS
|
On-site presentation
Pierre-Alexis Chaboche, Wakiyama Yoshifumi, Hyoe Takata, Toshihiro Wada, Olivier Evrard, Toshiharu Misonou, Takehiko Shiribiki, and Hironori Funaki

The Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident trigged by the Great East Japan Earthquake and subsequent tsunami in March 2011 released large quantities of radionuclides in terrestrial and marine environments of Fukushima Prefecture. Although radiocaesium (i.e. 134Cs and 137Cs) activity in these environments has decreased since the accident, the secondary inputs via the rivers draining and eroding the main terrestrial radioactive plume were shown to sustain high levels of 137Cs in riverine and coastal sediments, which are likely deposited off the coast of the Prefecture. Accordingly, identifying the sources of sediment is required to elucidate the links between terrestrial and marine radiocaesium dynamics and to anticipate the fate of persistent radionuclides in the environment.

The objective of this study is to develop an original sediment source tracing technique to quantify the riverine sources of sediment and associated radionuclides accumulated in the Pacific Ocean. Target coastal sediment cores (n=6) with a length comprised between 20 and 60cm depth were collected during cruise campaigns between July and September 2022 at the Ota (n=2), Niida (n=1) and Ukedo (n=3) river mouths. Prior to gamma spectrometry measurements, sediment cores were opened and cut into 2 cm increments, oven-dried at 50°C for at least 48 hours, ground and passed through a 2-mm sieve.

Preliminary results regarding the spatial and depth distribution of radiocaesium in these samples show a strong heterogeneity, with highest radiocaesium levels (up to 134 ± 2 and 4882 ± 11 Bq kg-1 for 134Cs and 137Cs, respectively) found in coastal sediment cores located at the Ukedo river mouth. On the opposite, no trace or low levels of Fukushima-derived radiocaesium were found in the Niida and in one sediment core of the Ota River mouths. Additional measurements will be conducted to determine the physico-chemical properties of this sediment, in order to select the optimal combination of tracers, which will then be introduced into un-mixing models. This increase knowledge will undoubtedly be useful for watershed and coastal management in the FDNPP post-accidental context.

How to cite: Chaboche, P.-A., Yoshifumi, W., Takata, H., Wada, T., Evrard, O., Misonou, T., Shiribiki, T., and Funaki, H.: Quantifying the riverine sources of sediment and associated radiocaesium deposited off the coast of Fukushima Prefecture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4697, https://doi.org/10.5194/egusphere-egu23-4697, 2023.

17:20–17:30
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EGU23-6019
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GI2.2
|
Virtual presentation
Roman Bezhenar, Hyoe Takata, and Vladimir Maderich

The 3D model THREETOX was applied for the long-term simulation of the planned release of radioactively contaminated water from Fukushima storage tanks to marine environment. Two radionuclides were considered: 3H that has the largest activity in tanks and 129I that can caused the largest dose of radiation to human. The constant release rate of 3H equal to 22 TBq/y according to TEPCO estimations and the constant release rate of 129I equal to 361 MBq/y according to estimations from the current study were used in the simulations.

The THREETOX model used monthly averaged currents from the KIOST-MOM model. A dynamic food web model was included in the THREETOX model. In the model, organisms uptake the activity directly from water and through the food chain. The food chain consists of phytoplankton, zooplankton, non-piscivorous (prey) fish, and piscivorous (predatory) fish. In case of 129I, macro-algae was also considered. The modelling area covers Fukushima coastal waters and extends for 1600 km from the coast to the East. From North to South this area extends for 1300 km.

From model results, we can see how contamination will spread along the coast in different seasons. For example, in summer time the currents near the coast are directed to the North that leads to contamination of the Sendai Bay. This means that at different points along the coast, the concentration of radionuclides can periodically change according to currents that change during the year. Calculated concentrations of activity at several points along the coast of Japan, which correspond to largest cities in the area of interest, were extracted from model results. For example, calculated concentration of 3H in water in Tomioka point, which is quite close to FDNPP, sometimes can exceed 200 Bq/m3. In Soma point, the concentration will exceed 50 Bq/m3, while in point Iwaki-Onahama – 20 Bq/m3 at some moments of time. In other points, the calculated concentration of 3H in water will not exceed 10 Bq/m3 that is less than background concentration 50 Bq/m3. Concerning 129I, its maximum concentration in water will be around 10-3 – 10-2 Bq/m3 in points close to FDNPP and around 10-4 Bq/m3 in points further from the NPP that is around 100 000 times less than the calculated concentrations of 3H.

Calculated concentrations of OBT (organically bounded tritium) in predatory and prey fish are less than 0.01 Bq/kg in all points except FDNPP point where it is around 0.02 Bq/kg. This value is 10 times less than measured concentration of OBT in fish (0.2 Bq/kg) that was made in 2014 in the coastal area near the damaged NPP. Calculated concentrations of 129I in predatory and prey fish are in the range 10-6 – 10-4 Bq/kg in all considered points. Concentrations of 129I in macro-algae are about 100 times higher due to ability of iodine to accumulate in macro-algae. 

How to cite: Bezhenar, R., Takata, H., and Maderich, V.: Transport of H-3 and I-129 in water and their uptake by marine organisms due to the planned release of Fukushima storage water, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6019, https://doi.org/10.5194/egusphere-egu23-6019, 2023.

17:30–17:54
17:54–18:00

Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X4

Chairpersons: Masatoshi Yamauchi, Hikaru Sato, Daisuke Tsumune
X4.197
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EGU23-1607
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GI2.2
Mizuo Kajino and Akira Watanabe

After the Fukushima nuclear accident, atmospheric 134Cs and 137Cs measurements were taken in Fukushima city for 8 years, from March 2011 to March 2019. The airborne surface concentrations and deposition of radiocesium (radio-Cs) were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The effective half-lives of 137Cs in the concentrations and deposition before 2015 (0.754 and 1.30 years, respectively) were significantly shorter than those after 2015 (2.07 and 4.69 years, respectively), which was likely because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. In fact, the dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. 

Resuspension of 137Cs from the contaminated ground surface to the atmosphere is essential for understanding the long-term environmental behaviors of 137Cs. We assessed the 137Cs resuspension flux from bare soil and forest ecosystems in eastern Japan in 2013 using a numerical simulation constrained by surface air concentration and deposition measurements. In the estimation, the total areal annual resuspension of 137Cs is 25.7 TBq, which is equivalent to 0.96% of the initial deposition (2.68 PBq). The current simulation underestimated the 137Cs deposition in Fukushima city in winter by more than an order of magnitude, indicating the presence of additional resuspension sources. The site of Fukushima city is surrounded by major roads. Heavy traffic on wet and muddy roads after snow removal operations could generate superlarge (approximately 100 μm in diameter) road dust or road salt particles, which are not included in the model but might contribute to the observed 137Cs at the site.

The current presentation based on the two published papers: Watanabe et al., ACP, https://doi.org/10.5194/acp-22-675-2022 (2022) and Kajino et al., ACP, https://doi.org/10.5194/acp-22-783-2022 (2022). The presenters would like to thank all of the co-authors of the two papers for their significant contributions.

How to cite: Kajino, M. and Watanabe, A.: Eight-year variations in atmospheric radiocesium in Fukushima city and simulated resuspension from contaminated ground surfaces in eastern Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1607, https://doi.org/10.5194/egusphere-egu23-1607, 2023.

X4.198
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EGU23-3049
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GI2.2
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ECS
Miyu Nakanishi, Yuichi Onda, Hiroaki Kato, Junko Takahashi, Hikaru Iida, and Momo Takada

Radionuclides released and deposited by the 2011 Fukushima Daiichi Nuclear Power Plant accident caused an increase in air dose rates in forests in Fukushima Prefecture. It has been reported that air dose rates increase during rainfall, but we found that air dose rates decreased during rainfall in forests in Fukushima. This is said to be due to the shielding effect of soil moisture. This study aimed to develop a method for estimating changes in air dose rates due to rainfall even in the absence of soil moisture data. Therefore, we used the preceding rainfall (Rw), an indicator that also takes into account past rainfall; we calculated Rw in Namie-Town, Futaba-gun, Fukushima Prefecture from May to July 2020, and estimated air dose rates. In this area, air dose rates decreased with increasing soil moisture. Furthermore, air dose rates could be estimated by combining Rw with a half-life of 2 hours and 7 days, and by considering hysteresis in the absorption and drainage processes. The coefficient of determination (R2) exceeded 0.70 for the estimation of soil water content at this time. Furthermore, good agreement was also observed in the estimation of air dose rates from Rw (R2 > 0.65). The same method was used to estimate air dose rates at the Kawauchi site from May to July 2019. Due to the high water repellency of the Kawauchi site, the increase in soil water content was very small and the change in air dose rate was almost negligible when soil water content was less than 15% and rainfall was less than 10 mm. This study enabled the estimation of soil water content and air dose rate from rainfall and captured the effect of rainfall on the decreasing trend of air dose rate. Therefore, in the future, This study can be used as an indicator to determine whether temporary changes in air dose rates are caused by influences other than rainfall. This study also contributes to the improvement of methods for estimating external dose rates for humans and terrestrial animals and plants in forests.

How to cite: Nakanishi, M., Onda, Y., Kato, H., Takahashi, J., Iida, H., and Takada, M.: Changes in Air Dose Rates due to Soil Water Content in Forests in Fukushima Prefecture, Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3049, https://doi.org/10.5194/egusphere-egu23-3049, 2023.

X4.199
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EGU23-4947
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GI2.2
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ECS
Takahiro Tatsuno, Hiromichi Waki, Naoto Nihei, and Nobuhito Ohte

A lot of radionuclides were scattered after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Previous studies showed that there were FDNPP-derived radioactive cesium-rich microparticles (CsMPs) with the size of a few μm in the soil and river water around Fukushima Prefecture[1]. CsMPs have high radioactive cesium (Cs) concentration per unit mass, therefore they can be one of the factor in overestimating the Cs concentration in samples. Because Cs in CsMPs may not react directly with clay particles unlike the Cs ion in liquid phase, it is considered that CsMPs work as Cs carrier in soils[2]. However, unlike ionic Cs and Cs adsorbed onto clay particles, the distribution and dynamics of CsMPs in soils have not been clarified. In this study, we investigated vertical distribution of CsMPs in the forest soil and the soil properties in Fukushima Prefecture, Japan.

Soil samples were collected from the forest in the difficult-to-return zone, approximately 10 km away from the FDNPP. The undisturbed soil samples were collected from 0-35 cm soil depth at 5 cm intervals using core sampler to investigate soil properties. Furthermore, litter samples on the surface soil layer were collected. Using these samples, the vertical distribution of Cs concentration in the soil and Cs derived from CsMPs were investigated. Cs concentration in samples placed in 100 mL of U8 container was measured using a germanium semiconductor detector. Cs derived from CsMPs was evaluated using an Imaging plate with reference to the method ffor quantification of CsMPs[3].

Like Cs adsorbed on the soil, CsMPs were also mostly distributed in the soil surface layer between o and 5 cm of soil depth. We considered that straining may be one of the mechanism of CsMPs retention on the soil surface. Bradford et al. (2006) [4] showed that straining might be a significant mechanism for colloid retention when the average particle size in the porous medium is less than 200 times larger than the colloidal particle size. In this study, assuming the CsMPs size of approximately 1 µm, the average particle size of the soil collected from surface layer 0-5 cm was less than 200 times that of CsMPs. However, the average particle size decreased in deeper layer than 5 cm, therefore, it was considered that straining mechanism could be stronger.

This work was supported by FY2022 Sumitomo Foundation and FY2022 Internal Project of Institute of Environmental Radioactivity, Fukushima University.

 

References

[1] Igarashi, Y. et al., 2019. J. Environ. Radioact. 205–206, 101–118.

[2]  Tatsuno, T et al., 2022. J. Environ. Manage. 329, 116983.

[3] Ikehara et al., 2018. Environ. Sci. Technol. 52, 6390–6398.

[4] Bradford et al., 2003. Environ. Sci. Technol. 37, 2242–2250.

How to cite: Tatsuno, T., Waki, H., Nihei, N., and Ohte, N.: Vertical distribution of radioactive cesium-rich microparticles in forest soil of Hamadori area, Fukushima Prefecture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4947, https://doi.org/10.5194/egusphere-egu23-4947, 2023.

X4.200
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EGU23-15515
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GI2.2
Yuma Niwano, Hiroaki Kato, Satoru Akaiwa, Donovan Anderson, Hikaru Iida, Miyu Nakanishi, Yuichi Onda, Hikaru Sato, and Tadafumi Niizato

Groundwater systems and surface water can interact in a complex manner that influences catchment discharge, which then becomes more complex in forest slopes. A large amount of Radioactive cesium (137Cs) deposited on forests due to the Fukushima Daiichi Nuclear Power Plant accident remains in terrestrial environments and is transported downstream as suspended or dissolved forms by surface water. Generally, the concentration of dissolved 137Cs in surface water increases especially during runoff. While the leaching behavior of 137Cs from contaminated forest materials and soils to surface water has been heavily studied, the influence of 137Cs concentration in shallow groundwater systems in forest slopes have not been investigated. Therefore, detailed hydrological observations of groundwater on a forest hillslope will enable quantitative analysis of the influence of groundwater flow on the formation of dissolved 137Cs concentrations in surface water during base flow and during runoff. Our results showed that the dissolved 137Cs concentration in surface water increases during water discharge. The average concentration of dissolved 137Cs in shallow groundwater was 0.64 Bq/L, which was higher than that in surface water (average 0.10 Bq/L). Furthermore, it was also observed that a part of the shallow groundwater on the slope moves toward the river channel at the time of water runoff. This suggests that shallow groundwater may have flowed into the surface water during the outflow and contributed to the increase of 137Cs in the surface water. In this study, the contribution of groundwater in forest slopes to the dissolved 137Cs concentration in surface water was estimated using the hydrodynamic gradient distribution of groundwater in forest slopes and the measured dissolved 137Cs concentration in groundwater.

How to cite: Niwano, Y., Kato, H., Akaiwa, S., Anderson, D., Iida, H., Nakanishi, M., Onda, Y., Sato, H., and Niizato, T.: 137Cs transport flux to surface water due to shallow groundwater discharge from forest hillslope, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15515, https://doi.org/10.5194/egusphere-egu23-15515, 2023.

X4.201
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EGU23-5042
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GI2.2
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ECS
Hikaru Sato, Naoaki Shibasaki, Maksym Gusyev, Yuichi Onda, and Dmytro Veremenko

Migration of long-lived radioactive 90Sr introduced by nuclear accidents and radioactive waste requires long-term monitoring and protection management due to its half-life of 28.8 years and high mobility in water. Presently, 37 years have passed since the largest worldwide 90Sr contamination was released and deposited around the Chornobyl Nuclear Power Plant (ChNPP). In the vicinity of the ChNPP, the water level of the cooling pond (CP) has declined since May 2014 following the decommissioning phase of the Unit 3 reactor. The drawdown of the CP lowered the groundwater level in a massive vicinity (about 70 km2), and the change in the groundwater system due to the drawdown has caused concerns about possible changes in 90Sr concentrations in water and transport dynamics to the Pripyat River. Therefore, this study evaluated how 90Sr transport dynamics were influenced due to changes in the groundwater flow system from 2011 to 2020 based on observed data and results of the groundwater flow simulation in the CP vicinity.

The numerical simulation was conducted from 2011 to 2020 on monthly time-step using USGS MODFLOW with PM11 GUI and calibrated to groundwater heads measured at monitoring wells. In the location between the CP and the Pripyat River, estimated pore velocities near the river were reduced compared to velocities before the CP drawdown due to the decrease in the hydraulic gradient between the CP and the river. Decrease in groundwater velocity results decrease in groundwater discharge and delay of 90Sr transport. Therefore, the amount of 90Sr transported from the CP to the river is smaller than the period prior to the CP drawdown. The reduced 90Sr transport is expected to have less impact on the radioactivity in the river water even in the Pripyat River floodplain northwest of the CP where 90Sr concentrations significantly increased after the CP drawdown. In addition, the measured and simulated changes in groundwater flow direction and velocity suggested the possibility of 90Sr accumulation at the floodplain caused by stagnant groundwater from reduced velocity and additional 90Sr infiltration from surrounding ponds located at the Pripyat River floodplain. Therefore, enhancing the current monitoring of 90Sr concentrations near the floodplain would be needed for long-term monitoring and protection management to prevent the risk.

How to cite: Sato, H., Shibasaki, N., Gusyev, M., Onda, Y., and Veremenko, D.: Changes in 90Sr transport dynamics in groundwater after large-scale groundwater drawdown in the vicinity of the cooling pond at the Chornobyl Nuclear Power Plant, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5042, https://doi.org/10.5194/egusphere-egu23-5042, 2023.

X4.202
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EGU23-10539
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GI2.2
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Highlight
Honoka Kurosawa, Kenji Nanba, Toshihiro Wada, and Yoshifumi Wakiyama

It is known that the semi-enclosed water area such as pond and dam reservoir is readily subject to 137Cs accumulation because of the secondary inflow from the catchment area. We present the long-term monitoring data of the 137Cs concentration in bottom sediment and pond water in an urban pond located in the central area of Koriyama City, Fukushima Prefecture to discuss the 137Cs dynamics of the urban pond. The pond was decontaminated by the bottom sediment removal in 2017. The bottom sediment core and pond water were collected in 2015 and 2018-2021. The inflow and outflow water were collected in 2020-2021. The river water around the pond was collected in 2021. The bottom sediment and water samples were measured for 137Cs concentration, particulate size distribution, and N and C stable isotopes. Compared between 2015 and 2018, the 137Cs inventory and 0-10 cm depth of 137Cs concentration in the bottom sediment at 7 points were decreased by 81 % (mean 1.50 to 0.28 MBq/m2) and 85 % (mean 31.5 to 4.8 kBq/kgDW), respectively. Although mean 137Cs inventory in bottom sediment did not drastically change during 2018-2021, its variability became wider. Points with increased 137Cs inventory in bottom sediment showed year-by-year increase in thickness of layer with concentrations higher than 8 kBq/kgDW, a criterion for considered decontamination. The 137Cs concentration in suspended solids (SS) in pond water was lowered after decontamination, although it still remained above 8 kBq/kgDW. The 137Cs concentrations in SS of inflow water were also high, exceeding 8 kBq/kgDW. The 137Cs concentration in SS of the river water around the pond was higher when it passed through the urban area, suggesting that the inflow of particles from urban origin maintained high 137Cs level in the pond. 

How to cite: Kurosawa, H., Nanba, K., Wada, T., and Wakiyama, Y.: Long-term dynamics of 137Cs accumulation at an urban pond, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10539, https://doi.org/10.5194/egusphere-egu23-10539, 2023.

X4.203
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EGU23-11671
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GI2.2
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Naoyuki Wada, Yuichi Onda, Xiang Gao, and Chen Tang

The Fukushima Daiichi Nuclear Power Plant accident (FDNPP) in 2011 resulted in the release of large amounts of Cs-137 into the atmosphere. Cs-137 deposited on land was mainly distributed in forests, but some of it has been discharged to the sea through rivers. The dissolved and suspended forms of Cs-137 in rivers have been focused on, and it is known that the discharge mechanism and concentration formation of Cs-137 differ depending on the land use in the river basin. On the other hand, there are few cases that focus on the dynamics of Cs-137 in river bottom sediments. River-bottom sediment is less likely to flow downstream than suspended sediments, so contamination in the downstream area may be long-term.
We will clarify the migration mechanism of Cs-137 in rivers including river-bottom sediment.Therefore, we will analyze data collected from 2011 to 2018 in 89 watersheds in Fukushima prefecture. In analyzing the data, we removed sampling points with brackish water using electrical conductivity and corrected for particle size to standardize the surface area of particles that absorb Cs-137.As a result, it was found that unlike dissolved and suspended forms, the Cs concentration in river-bottom sediments can increase within the initial year. This is related to the average initial deposition in the watershed and the amount of initial deposition at the river-bottom sediment sampling sites, with a tendency to increase with relatively higher initial deposition in the upstream area. It was also known that the decrease in suspended Cs concentration was more pronounced when anthropogenic activities in the watershed were more active, but there was no clear relationship between land use in the watershed and changes in river-bottom sediment Cs concentration. This indicates that suspended sediment Cs concentrations are controlled by initial deposition to suspended sediment production sources, whereas river-bottom Cs concentrations are controlled by multiple factors such as sediment traction and Cs supply from river water.

How to cite: Wada, N., Onda, Y., Gao, X., and Tang, C.: Changes in Cs-137 concentrations in river-bottom sediments and their factors in Fukushima Prefecture rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11671, https://doi.org/10.5194/egusphere-egu23-11671, 2023.

X4.204
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EGU23-2540
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GI2.2
Yasunori Igarashi, Yuichi Onda, Koki Matsushita, Hikaru Sato, Yoshifumi Wakiyama, Hlib Lisovyi, Gennady Laptev, Dmitry Samoilov, Serhii Kirieiev, and Alexei Konoplev

Concentration-discharge relationships are widely used to understand the hydrologic processes controlling river water chemistry. We investigated how hydrological processes affect radionuclide concentrations (137Cs and 90Sr) in surface water in the headwater catchment at the Chornobyl exclusion zone in Ukraine. In flat wetland catchment, the depth of saturated soil layer changed little throughout the year, but changes in saturated soil surface area during snowmelt and immediately after rainfall affected water chemistry by changing the opportunities for contact between suface water and the soil surface. On the other hand, slope catchments with little wetlands, the water chemistry in river water is formed by changes in the contribution of "shallow water" and "deep water" due to changes in the water pathways supplied to the river. Dissolved and suspended 137Cs concentrations did not correlate with discharge rate or competitive cations, but the solid/liquid ratio of 137Cs showed a significant negative relationship with water temperature, and further studies are needed in terms of sorption/desorption reactions. 90Sr concentrations in surface water were strongly related to water pathways for each the catchments. The contact between surface water and the soil surface and the change in the contribution of shallow and deep water to stream water could changes 90Sr concentrations in surface water for in wetland and slope catchments, respectively. In this study, we revealed that the radionuclide concentrations in rivers in Chornobyl is strongly affected by the water pathways at headwater catchments.

How to cite: Igarashi, Y., Onda, Y., Matsushita, K., Sato, H., Wakiyama, Y., Lisovyi, H., Laptev, G., Samoilov, D., Kirieiev, S., and Konoplev, A.: Hydrological setting control 137Cs and 90Sr concentration at headwater catchments in the Chornobyl Exclusion Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2540, https://doi.org/10.5194/egusphere-egu23-2540, 2023.

X4.205
|
EGU23-10093
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GI2.2
Yoshifumi Wakiyama, Hyoe Takata, Keisuke Taniguchi, Takuya Niida, Yasunori Igarashi, and Alexei Konoplev

Understanding riverine 137Cs dynamics during high-flow events is crucial for improving predictability of 137Cs transportation and relevant hydrological responses. It is frequently documented that the majority of 137Cs is exported during high-flow events triggered by intensive rainfall. Studies on 137Cs in coastal seawater suggested that a huge high-flow events resulted in high dissolved 137Cs concentration in seawater. Different temporal patterns of 137Cs concentrations in river water are found in the existing literature on 137Cs dynamics during high-flow events. Although such differences may reflect catchment characteristics, there is no comprehensive analysis for the relationships. This study explores catchment characteristics affecting 137Cs transport via river to ocean based on datasets obtained by sampling campaigns during high-flow events. 137Cs datasets obtained at 13 points in 6 river water systems were subject to the analysis. The analyses intended to explore relationship between catchment characteristics (scale and land use composition) and 137Cs dynamics in terms of variations in concentration, fluxes, and potential remobilization in seawater. We could not find any significant correlations between the parameters of catchment characteristics and mean values of normalized concentrations of 137Cs and apparent Kd. However, when approximating 137Cs concentrations and Kd value as a power function of suspended solid concentration (Y=α X^β), the power of β in the equations for dissolved 137Cs concentration and Kd showed negative and positive correlations with the logarithm of the watershed area, respectively, and the positive β was found when the catchment area was on the order of 100 km2 or larger and vice versa. This indicates that the concentration of dissolved 137Cs tends to decrease with increased water discharge in larger catchments for smaller catchments. These results suggest that the temporal pattern of dissolved 137Cs concentrations depends on watershed scale. 137Cs flux during a single event ranged from 1.9 GBq to 1.1 TBq and accounted for 0.00074% to 0.22% of total 137Cs deposited in relevant catchments. Particulate 137Cs flux accounted for more than 92% of total 137Cs flux, except for Ukedo River basin with a large dam reservoir. R-factor, an erosivity index in the Universal Soil Loss Equation model family, is a good parameter for reproducing sediment discharge and particulate 137Cs flux. Efficiency of particulate 137Cs flux, calculated by dividing the flux by R-factor of event, tended to be high in catchments with relatively low forest cover. Desorption ratio of 137Cs, obtained by 1-day shaking experiment of SS in seawater, ranged from 2.8 to 6.6%. The ratio was almost proportional of ratio of exchangeable 137Cs. The estimated amounts of desorbed 137Cs, obtained by multiplying particulate 137Cs and the desorption ratios, were greater than direct flux of dissolved 137Cs. Reanalysis of riverine 137Cs dataset in high flow events is revealing relationship between catchment characteristics and 137Cs dynamics. Further analyses, such as evaluation of decontamination impacts and inter-catchment comparisons of 137Cs fluxes, are required for better understanding.

How to cite: Wakiyama, Y., Takata, H., Taniguchi, K., Niida, T., Igarashi, Y., and Konoplev, A.: Riverine 137Cs dynamics and remoralization in coastal waters during high flow events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10093, https://doi.org/10.5194/egusphere-egu23-10093, 2023.

X4.206
|
EGU23-10868
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GI2.2
Shun Satoh and Hyoe Takata

Due to the accident at the Fukushima Daiichi Nuclear Power Plant (1F) in March 2011, radionuclides were introduced into the environment, and one of the release pathways to the ocean is the direct discharge from the 1F (on-going release). This was mainly caused immediately after the accident, but even now, the on-going release is continuing. In this study, firstly we estimated the on-going release of 137Cs from 1F over 10 years after the accident, using the TEPCO’s 137Cs monitoring results in the coastal area around 1F. Secondly, change in the monitoring data related to countermeasures by TEPCO (e.g. construction of iced walls) to reduce the introduction of contaminated water into the ocean or detect 137Cs in nearby seawater, so their effects on the on-going release estimation were also discussed. A box model including inside and outside of the port was assumed for the area around 1F, and the amount of 137Cs in the box was estimated (estimated value: modeled data). Then, the difference between the estimated value and the amount of 137Cs obtained from actual observed concentrations (measured value: monitoring data) was calculated. The result showed that the measured value was higher than the estimated value, suggesting the on-going release from 1F. As for decrease in monitoring data after the countermeasures, it is implied that the estimation of rate of on-going release has been reduced by the countermeasures.

How to cite: Satoh, S. and Takata, H.: Estimation of annual Cesium-137 influx from the FDNPP to the coastal water, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10868, https://doi.org/10.5194/egusphere-egu23-10868, 2023.

X4.207
|
EGU23-2561
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GI2.2
Kyeong Ok Kim, Vladimir Maderich, Igor Brovchenko, Kyung Tae Jung, Sergey Kivva, Katherine Kovalets, and Haejin Kim

A generalized model of scavenging of the reactive radionuclide 239,240Pu was developed, in which the sorption-desorption processes of oxidized and reduced forms on multifraction suspended particulate matter are described by first-order kinetics. One-dimensional transport-diffusion-reaction equations were solved analytically and numerically. In the idealized case of instantaneous release of 239,240Pu on the ocean surface, the profile of concentrations asymptotically tends to the symmetric spreading bulge in the form of a Gaussian moving downward with constant velocity. The corresponding diffusion coefficient is the sum of the physical diffusivity and the apparent diffusivity caused by the reversible phase transitions between the dissolved and particulate states. Using the method of moments, we analytically obtained formulas for both the velocity of the center mass and apparent diffusivity. It was found that in ocean waters that have oxygen present at great depths, we can consider in the first approximation a simplified problem for a mixture of forms with a single effective distribution coefficient, as opposed to considering the complete problem. This conclusion was confirmed by the modeling results for the well-ventilated Eastern Mediterranean. In agreement with the measurements, the calculations demonstrate the presence of a maximum that is slowly descending for all forms of concentration. The ratio of the reduced form to the oxidized form was approximately 0.22-0.24. At the same time, 239,240Pu scavenging calculations for the anoxic Black Sea deep water reproduced the transition from the oxidized to reduced form of 239,240Pu with depth in accordance with the measurement data.

How to cite: Kim, K. O., Maderich, ., Brovchenko, ., Jung, . T., Kivva, ., Kovalets, ., and Kim, .: Dispersion of particle-reactive elements caused by the phase transitions in scavenging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2561, https://doi.org/10.5194/egusphere-egu23-2561, 2023.

X4.208
|
EGU23-4925
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GI2.2
Daisuke Tsumune, Frank Bryan, Keith Lindsay, Kazuhiro Misumi, Takaki Tsubono, and Michio Aoyama

Radioactive cesium (137Cs) is distributed in the global ocean due to global fallout from atmospheric nuclear tests, release from reprocessing plants in Europe, and supply to the ocean due to the Fukushima Daiichi Nuclear Power Plant accident. In order to detect future contamination by radionuclides, it is necessary to understand the global distribution of radionuclides such as 137Cs. For this purpose, the IAEA is compiling a database of observation results (MARIS). However, since the spatio-temporal densities of observed data vary widely, it is difficult to obtain a complete picture from the database alone. Comparative validation using ocean general circulation model (OGCM) simulations is useful in interpreting these observations, and global ocean general circulation model (CESM2, POP2) simulations were conducted to clarify the behavior of 137Cs in the ocean. The horizontal resolution is 1.125° longitude and 0.28° to 0.54° latitude. The minimum spacing near the sea surface is 10 m, and the spacing increases with depth to a maximum of 250 m with 60 vertical levels. Climatic values were used for driving force. As a source term for 137Cs to the ocean, atmospheric fallout from atmospheric nuclear tests was newly established based on rainfall data and other data, and was confirmed to be more reproducible than before. Furthermore, the release from reprocessing plants in Europe and the leakage due to the accident at the Fukushima Daiichi Nuclear Power Plant were taken into account. 2020 input conditions were assumed to continue after 2020, and calculations were performed from 1945 to 2030. The simulated 137Cs activities were found to be in good agreement, especially in the Atlantic and Pacific Oceans, where the observed densities are large. On the other hand, they were underestimated in the Southern Hemisphere, suggesting the need for further improvement of the fallout data. 137Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident in March 2011 were generally in good agreement, although the reproducibility remained somewhat problematic due to insufficient model resolution. In other basins, the concentration characteristics were able to be determined, although the observed values were insufficient. Radioactivity concentrations of atmospheric nuclear test-derived 137Cs may continue to be detected in the global ocean after 2030. The results of this simulation are useful for planning future observations to fill the gaps in the database.

How to cite: Tsumune, D., Bryan, F., Lindsay, K., Misumi, K., Tsubono, T., and Aoyama, M.: Verification of reproductivity of 137Cs activity concentration in the database by an ocean general circulation model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4925, https://doi.org/10.5194/egusphere-egu23-4925, 2023.

Posters virtual: Wed, 26 Apr, 10:45–12:30 | vHall ESSI/GI/NP

vEGN.6
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EGU23-13486
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GI2.2
|
ECS
Satoru Ohtsuki, Yuhei Shirotani, and Hyoe Takata

For decommissioning of Fukushima Daiichi Nuclear Power Station (FDNPS), it is one of the biggest problems to treat the radioactive contaminated stagnant water in the building. It is difficult to remove H-3 from the contaminated water by only Advanced Liquid Processing System (ALPS) treatment. Thus, the Japanese Government announced to release the ALPS treated water containing H-3. To predict the alteration of the dose rate of the marine biota by the change of H-3 concentration in marine water after the release of ALPS water, it is necessary to understand the dynamics of H-3 in marine ecosystem. In this study, we studied the behavior of H-3 in the marine environment (water and biota) off Aomori and Iwate prefectures from FY2003 to FY2012, as the background data of the Pacific Ocean along the coast of the North East Japan. To clarify the dynamics of H-3 in marine biota, we compared H-3 and Cs-137. Excluding the period of the intermittent test operation of the Rokkasho Reprocessing Plant (FY2006-FY2008), the concentration of H-3 in seawater, tissue free water tritium (TFWT) and organically bound tritium (OBT) were 0.052-0.20 Bq/L with a mean of 0.12±0.031 Bq/L, 0.050-0.34 Bq/kg-wet with a mean of 1.1±0.039 Bq/kg-wet and 0.0070-0.099 Bq/kg-wet with a mean of 0.042±0.019 Bq/kg-wet, respectively. Before the FDNPS accident (FY2003-FY2010), Cs-137 concentration in seawater and marine biota were 0.00054-0.0027 Bq/L with a mean of 0.0016±0.00041 Bq/L and 0.022-1.8 Bq/kg-wet with a mean of 0.090±0.037 Bq/kg-wet, respectively. Concentration Ratio (CR), the ratio of the concentration of marine biota and seawater for TFWT, was to be 0.34-2.37 with a mean of 0.97±0.31 in all spices, meaning the concentration of marine biota was almost equal to seawater. For Cs-137, CR were 46-78 with a mean of 56±22. We compared CRs for TFWT of Gadus macrocephalus, Lophius litulon and Oncorhynchus keta with those of Cs-137. Comparing CR-TFWT and CR-Cs-137 for these three species, Spearman-R was <0.4 and p was >0.05, indicating that the dynamics of TFWT and Cs-137 in marine ecology is decoupled.

How to cite: Ohtsuki, S., Shirotani, Y., and Takata, H.: Distributions of tritium in the marine water and biota around Rokkasho Reprocessing Plant, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13486, https://doi.org/10.5194/egusphere-egu23-13486, 2023.