Initiation of radioecological monitoring of forest soils and plants at the Lithuanian border region before the start of the Belarusian nuclear power plant operation.

Knowledge of the background activity concentrations of anthropogenic radionuclides before the start of operation of the new nuclear power plant in Belarus, BelNPP, is an issue of great importance for neighbouring countries. In this study, we provide the pilot characterisation of the Lithuanian part of the 30-km zone of the BelNPP, emphasising the forest plants, terrestrial mosses, forest organic and mineral topsoil to describe the preoperational radioecological state of the pine forest ecosystem. Key anthropogenic radionuclides (14C, 3H, 137Cs and 239,240Pu) were analysed. The 14C specific activity varied from 97.80 ± 1.30 to 102.40 ± 0.79 pMC. The 3H specific activity in the tissue-free water tritium form varied from 13.2 ± 2.2 TU to 20.8 ± 2.3 TU, which corresponded to the 3H level of precipitation in this region. The activity concentrations of 239,240Pu in soil and moss samples did not exceed 1 Bq/kg and were mainly due to global fallout after nuclear tests. The 137Cs inventory in the pine forest soils of the Lithuanian part of the BelNPP 30-km zone varied from 930 ± 70 to 1650 ± 430 Bq/m2. High variation of the inventory and uneven distribution in the soil profile conditioned a wide range of 137Сs activity in terrestrial plants from 1.0 ± 0.5 to 40.5 ± 1.8 Bq/kg dry weight. The abundance of microorganisms in different seasons and soil depths do not exceed the natural levels. According to PCA loads, the number of microorganisms and variability of 137Cs specific activity is determined by soil abiotic parameters.

Baltic Sea water tritium and stable isotopes in 2016-2017.

Water samples from the different basins of the Baltic Sea and North Sea were collected during four cruises taken place in 2016-2017. Altogether 60 water samples for 3H activity concentration and 120 water samples for stable isotopes ratio (δ18O and δ2H) were analysed. Exceptionally strong inflow activity from North Sea to the Baltic Sea occurred prior our surveys. The data obtained enabled comprehensive evaluation of tritium and stable isotopes distribution in waters of Baltic Sea and contributing inputs, including riverine and atmospheric freshwater flux and saline water inflow through the Danish Straits. By comparing with the previous studies, we noticed a tendency toward an increase in the δ18O and δ2H values of zero-salinity component over time, which may be due to climate change. In the case of tritium, the influence of artificial sources has also been noticed.

The distribution of tritium in aquatic environments, Lithuania.

The aim of this study is to investigate mobile radionuclide tritium (3H or T) activity dynamics in aquatic environments related to Ignalina NPP (INPP) site and water bodies located in remote areas unaffected by the INPP. The 3H excess in the INPP environment was analyzed and compared to the variable 3H background level over the period of operation of the INPP (end of 1983 - end of 2009) and during the initial stage of decommissioning (2010-2017). 3H in the INPP vicinity has been studied in the water of artificial channels related to operation of the INPP and site drainage, in natural surface water bodies and, at a smaller scale, in unconfined groundwater. This study presents an extensive 3H data set extending back to 1980, i.e. before INPP operation started. To assess the contribution of global sources to 3H dynamics, monthly precipitation was also studied, along with water from the Baltic Sea, Curonian Lagoon and Nemunas River were studied as well, all three of these located in the Lithuanian maritime zone. The 3H activity concentration in water was measured using liquid scintillation counting (LSC) techniques (direct counting and counting after enrichment). During the period of INPP operation, 3H from liquid effluent could be clearly observed in discharge channels, occurring in rather low diluted conditions, as well as in Lake Druksiai, the cooling basin, at an even more diluted level. The highest 3H activity concentration in Lake Druksiai was observed in 2003 and reached 201.3 ± 1.3 TU at a time when 3H activity concentrations in background water bodies was 9.2 ± 3.5 TU. After the closure of the INPP, the 3H liquid effluent rate reduced by approximately two orders of magnitude (from 1012 Bq in 1991 to 1010 Bq in 2016) and when decommissioning activity commenced then the 3H activity concentration fell to that approaching the background level (19-27 TU) that can still be observed in industrial discharge and rainwater drainage channels. 3H as a result of leakage from the INPP can be observed in groundwater only in direct proximity to the INPP site near the radioactive waste storage zone.

Investigations of the unsaturated zone at two radioactive waste disposal sites in Lithuania.

The unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium ((3)H) and stable isotope ratio ((18)O/(16)O and (2)H/(1)H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater.

Carbon-14 in tree rings and other terrestrial samples in the vicinity of Ignalina Nuclear Power Plant, Lithuania.

The results of (14)C measurements in the annual tree rings from the Ignalina Nuclear Power Plant (INPP) surroundings, Lithuania, for the period of its operation from 1984 to 2002 are presented. The terrestrial samples, mainly moss and related soil, are studied in places as well. The tree rings have shown slightly enhanced (14)C activity due to operation of the nuclear power plant. The maximal calculated normalized (14)C release of 11TBqGW(e)(-1)year(-1) and the maximal effective dose of 2.0x10(-3)mSvyear(-1) resulting from the (14)C were estimated for 1999. For other years of INPP operation these values are lower. The excess of (14)C specific activity measured in the moss and soil samples from moss-covered sites near the nuclear power plant (up to 0.5km) showed highly elevated (14)C contents (up to 813pMC), probably indicating releases of particulate material.