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The highest activities of (131)I, (134)Cs, and (136)Cs were found in fresh snow precipitated on 02 April 2011, at 0.83, 0.092, and 0.002 Bq L(-1) of meltwater, respectively. The (131)I/(134)Cs ratio decreased from 9.0 on 02 April to 1.2 on 27 April, which is consistent with the radioactive decay of (131)I. This fallout can only have originated from the accidental emission of Fukushima Nuclear Power Plant, Japan, in March 2011.

The long-term operation of three reactors and the radiochemical plant of the Mining-and-Chemical Combine (MCC), Russia’s largest producer of weapons-grade plutonium, has resulted in radioactive contamination of the Yenisei River floodplain. From 1995 to 2016, we found more than 200 radioactive particles (RP) in the Yenisei floodplain, downstream of the MCC. Analytical characterization showed that most of the RP were fuel particles, which were carried into the river after incidents at the MCC reactors. Having compared the 137Cs/134Cs ratios in the particles, we determined three time intervals when the RP were formed. The plutonium isotope ratios (238Pu/239,240Pu) vary substantially between the particles and indicate several different source terms. In addition to fuel RP, we found particles that only contained activation products (60Co or europium isotopes). SEM and γ-spectrometry showed that the cobalt particles could have originated from the corrosion of the reactor coolant system and the europium particles – from the damaged compensating rods. No europium particles have been found anywhere else in the world. The presence of RP from different sources (fuel, cobalt, and europium particles) in the Yenisei River floodplain makes this region a unique site for studying environmental effects of the particles. These RP represent point sources of radioecological significance.

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Abstract.The results of investigation of radioactive contamination of the river Yenisei bed pebbles in an influence zone of the KMCC (especially in its near-field part) are presented in this work. It is demonstrated, that pebbles can contain up to 30 % of the total amount of -emitting technogenic radionuclides (TRN) in the places with overlying soils. In addition, river bed pebbles, situated in permanently washing riverside sections of islands and banks, can contain significant amount of TRN too. These facts considerably increase an estimation of TRN reserves in the Yenisei floodplain. Without the contribution of the river bed pebbles the fraction of TRN, accumulated in the underlying and tow path pebbles in the near and far-field influence zones of the KMCC, can reach 7,9% for 137 Cs, 5,8% for 152 Eu, 5,6% for 154 Eu and <3% for 60 Co of their total amount.