Distribution of artificial gamma-ray emitting radionuclide activity concentration in the top soil in the vicinity of the Ignalina Nuclear Power Plant and other regions in Lithuania

The impact of the operating Ignalina Nuclear Power Plant (INPP) on the contamination of top soil layer with artificial radionuclides has been studied. Results of the investigation of artificial gamma-ray emitting radionuclide distribution in soil in the vicinity of the INPP and distant regions in Lithuania in 1996-2008 (INPP operational period) show that nowadays Cs-137 remains the most important artificial gamma-ray emitting radionuclide in the upper soil layer. Mean Cs-137 activity concentrations in the top soil layer in the vicinity of the INPP were found to be significantly lower compared to those in remote regions of Varena and Plunge (similar to 300 km from INPP). In 1996 and 1998 mean Cs-137 activity concentrations were in the range of 28-45 Bq/kg in the nearest vicinity to the INPP, 103 Bq/kg in Varena and 340 Bq/kg in Plunge region. Cs-137 activity concentrations were 5-20 times lower in meadow soil (4-14 Bq/kg) compared to swamp and forest soil. Co-60, the INPP origin radionuclide, was detected in samples only in 1996 and 2000, and the activity concentration of Co-60 was found to be in the range from 0.4 to 7.0 Bq/kg at the sampling ground nearest to the INPP. Average annual activity concentrations of the INPP origin Cs-137 and Co-60 in the air and depositions in the INPP region were modeled using Pasquill-Gifford equations. The modeling results of Cs-137 and Co-60 depositional load in the INPP vicinity agree with the experimentally obtained values. Our results provide the evidence that the operation of INPP did not cause any significant contamination in soil surface. (C) 2012 Elsevier B.V. All rights reserved