Ten-year radiocesium fluvial discharge patterns from watersheds contaminated by the Fukushima nuclear power plant accident

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

In the context of elevated concerns related to nuclear accidents and warfare, the lessons learnt from the Fukushima Daiichi Nuclear Power Plant accident in 2011 are important. In particular, Japanese authorities implemented an ambitious decontamination program to reduce the air dose rate in order to facilitate the return of the local inhabitants to previously evacuated areas. This approach contrasts the strategy adopted in Chernobyl, where the most contaminated areas remain off limits. Nonetheless, the effectiveness of the Japanese decontamination strategy on the dispersion of radioactive contaminant fluxes across mountainous landscapes exposed to typhoons has not been quantified. Based on the unique combination of river monitoring and modeling in a catchment representative of the most impacted area in Japan, we demonstrate that decontamination of 16% of the catchment area resulted in a decrease of 17% of sediment-bound radioactive fluxes in rivers. Decontamination operations were therefore relatively effective, although they could only be conducted in a small part of the area due to the dominance of steep forested slopes. In fact, 67% of the initial radiocesium contamination was calculated to remain stored in forested landscapes, which may contribute to future downstream radiocesium dispersion during erosive events. Given that only a limited proportion of the initial population had returned in 2019 (~30%), it raises the question as to whether decontaminating a small percentage of the contaminated area was worth the effort, the price, and the amount of waste generated?

Nanodispersion of ferrocianides for purification of man-made contaminated water containing caesium

A method of obtaining a nanodispersion of nickel-potassium ferrocyanides intended for purification of man-made polluted waters is proposed. It is applicable to purify effluent and floor drain water at nuclear power plants, which contains caesium, strontium, cobalt, manganese and other transition metals. The optimal conditions for the synthesis of nanodispersion have been determined, which is represented by clusters of nanoparticles associated with water molecules and nitrates dispersed in a dilute solution of nickel and potassium nitrates. On the surface of the formed nanocrystals there are fragments of structures of smaller formations. The mechanism of sorption of ions of alkali, alkaline earth and transition metals is investigated considering the ion charge density. The effect of competing ions (strontium, cobalt, manganese) on the sorption of caesium is taken into account. An integrated method of purification of multi-component man-made solutions including drainage waters of nuclear power plants is based on the use of nanodispersion of nickel-potassium ferrocyanides in combination with bentonite clay, which allows removing caesium from the drainage simulator with an efficiency of 96%, and strontium and transition metal ions (cobalt, manganese, copper, iron) with an efficiency of at least 98%.

Fukushima and Chernobyl: Similarities and Differences of Radiocesium Behavior in the Soil-Water Environment

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 the migration rates of ¹³⁷Cs in the environment and rates of its natural attenuation. In Fukushima areas, ¹³⁷Cs was strongly bound to soil and sediment particles, with its bioavailability being reduced as a result. Up to 80% of the deposited ¹³⁷Cs on the soil was reported to be incorporated in hot glassy particles (CsMPs) insoluble in water. Disintegration of these particles in the environment is much slower than that 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. Among the common features in the ¹³⁷Cs behavior in Chernobyl and Fukushima are a slow decrease in the ¹³⁷Cs activity concentration in small, closed, and semi-closed lakes and its particular seasonal variations: increase in the summer and decrease in the winter.

TEMPORAL VARIATION IN RADIOCESIUM CONCENTRATIONS IN WATERS OF THE NATSUI AND SAME RIVERS, SOUTH FUKUSHIMA PREFECTURE, JAPAN FROM 2011 TO 2020

In order to determine the long-term impacts of radiocesium contamination on ecosystems in watersheds and coastal areas following the Fukushima Daiichi Nuclear Power Plant accident in March 2011, it was important to monitor the transport behavior of radiocesium from an early stage. In this study, conducted from July 2011 to October 2020, we carried out field research along the Natsui and Same rivers running through watersheds in the south of Fukushima Prefecture, Japan, in which there had been a relatively low accumulation of radiocesium. We found that under normal flow conditions, the total (dissolved + particulate phase) activity of 137Cs decreased with increasing time following the accident. However, the water samples collected after rain events showed higher activity of up to 895 mBq l-1 with a higher percentage (>92% of total) of the particulate phase. These findings indicate that radiocesium deposited on the ground surface is predominantly transported in the particulate phase from watersheds to rivers via precipitation. The decontamination process, which was performed in the farmland during December 2014 to March 2015 and in forest during February 2013 to April 2014, was small effects of the transport of 137Cs. Under normal flow conditions, total 137Cs activity was largely determined by the suspended solids (SS) concentration and/or 137Cs concentration in the SS.