Radiocesium distribution and mid-term dynamics in the ponds of the Fukushima Dai-ichi nuclear power plant exclusion zone in 2015-2019.

This study analyzes the 137Cs behavior in the ponds of Okuma Town from 2015 to 2019 in the Fukushima Dai-ichi nuclear power plant (FDNPP) exclusion zone. A decline in both particulate and dissolved 137Cs activity concentrations was revealed. The decline rate constants for the particulate 137Cs activity concentration were found to be higher than for the dissolved 137Cs activity concentration. In terms of seasonality the dissolved 137Cs concentrations were higher from June to October, depending on the specific pond and year, most likely due to temperature dependence of 137Cs desorption from frayed edge sites of micaceous clay minerals. The apparent Kd(137Cs) in the studied ponds, in absolute value, appeared to be much higher than that for closed and semi-closed lakes of the Chernobyl contaminated area; however, these were comparable to the values characteristic of the rivers and reservoirs of the FDNPP contaminated area. The apparent Kd(137Cs) in the suspended sediment-water system was observed to decrease over time. It was hypothesized that this trend was associated with the decomposition of glassy hot particles. Relying on the theory of selective sorption and fixation, the exchangeable radiocesium interception potential, RIPex(K) was estimated using data on 137Cs speciation in the surface bottom-sediment layer and its distribution in the sediment-water system. For the studied ponds, RIPex(K) was on the average 2050 mEq/kg, which is within the range of values measured in laboratory studies reported in the literature.

Detailed study of post-Chernobyl Cs-137 redistribution in the soils of a small agricultural catchment (Tula region, Russia).

A detailed study of 137Cs redistribution was conducted within a small agricultural catchment in the highly contaminated Plavsk radioactive hotspot in the Tula region of Central Russia, 32 years after the Chernobyl nuclear power plant (NPP) accident, which occurred on April 26, 1986. Although more than three decades have passed since the Chernobyl NPP incident, 137Cs contamination is high. The 137Cs inventory varies from 67 to 306 kBq·m-2, which is 2-6 times higher than the radiation safety standard; however, the soils remain suitable for crop cultivation. The initial 137Cs fallout within the Plavsk radioactive hotspot was extremely heterogeneous, with a trend of decreasing 137Cs inventories from the NW to the SE directions within the studied territory. Contemporary 137Cs inventories are also very heterogeneous in the studied catchment. However, the trend of the initial 137Cs fallout does not appear in the contemporary 137Cs inventories on the slopes. Two methods of interpolation (expert-visual and automatic) were used to calculate the 137Cs budget, revealing high similarity in their 137Cs loss estimates; however, a large discrepancy was observed in their 137Cs gain estimates. A detailed analysis of 137Cs redistribution revealed the importance of hollows and "plow ramparts" (positive topographic forms on the boundaries of cultivated fields) in the transport and deposition of sediments. A quarter of the total 137Cs gain was deposited within the arable land, whereas a quarter was deposited within the non-plowing sides of the dry valley; the other half was deposited in the valley bottom. About 7-8 × 106 kBq of the 137Cs inventory flowed out of the catchment area, which was only about 2% of the 137Cs fallout after the Chernobyl NPP accident. About 89% of the total 137Cs reserve is concentrated in the top (0-25 cm) layer of soils, regardless of land use or location within the catchment.

Use of natural and artificial radionuclides to determine the sedimentation rates in two North Caucasus lakes.

The specific activities of natural (210Pb, 226Ra, and 232Th) and artificial (137Cs, 239,240Pu, and 241Am) radionuclides in the sediments of two North Caucasus lakes were determined. The two lakes, Lake Khuko and Lake Donguz-Orun, differ in their sedimentation conditions. Based on the use of unsupported 210Pbex and both Chernobyl-derived and bomb-derived 137Cs as chronological markers, it was established that the sedimentation rates in Lake Khuko over the past 55-60 y did not exceed 0.017 cm y-1. Sedimentation rates in Lake Donguz-Orun were found to be more than an order of magnitude higher. In the latter case, the sedimentation rates for the period from 1986 to the present were over 1.5 times higher than they were for the period 1963-1986. The differences in sedimentation rates were due to differences in the rates of denudation of their respective catchment areas. The specific activities of artificial radionuclides (137Cs, 2600 Bq kg-1; 239,240Pu, 162 Bq kg-1; and 241Am, 36 Bq kg-1) and their ratios in the sediments of Lake Khuko show that their deposition was mainly due to global stratospheric fallout of technogenic radionuclides associated with nuclear bomb testing during 1954-1963-rather than fallout from the Chernobyl accident. Several factors, including the mode of precipitation, features of the surface runoff, and location of Lake Khuko, were responsible for the accumulation of artificial radionuclides.