engleski

Environmental 14C and 3H levels in Croatia

A part of activities of Laboratory for low-level Radioactivities of the Ruđer Bošković Institute, Zagreb, Croatia, is devoted to monitoring 3H in precipitation and 14C in the atmosphere and biosphere. An overview of the results and comparison with the global trends is presented in the talk. Results of monitoring 14C activity in the atmosphere and in biological samples in the vicinity of the Nuclear Power Plant Krško in Slovenia, about 30 km from Zagreb, are also presented. Activity concentration of 3H was measured by gas proportional counting technique until 2007 and since 2008 by liquid scintillation counting after electrolytic enrichment. A gas proportional counting technique for 14C was replaced by liquid scintillation counting following either benzene synthesis or direct absorption of CO2. Long-term data on 3H activity concentration in monthly precipitation in Zagreb and Ljubljana (Slovenia) exist for the period since 1976 and 1981, respectively, while for shorter periods of time the data exist for several stations along the Adriatic coast and for the continental station Plitvice Lakes (Croatia). The long-term data records show seasonal variations superposed on the basic decreasing trend of mean annual values. The data recorded during last 2 decades, however, show almost constant mean annual 3H activity concentration of about 9 TU for the continental stations, while for coastal stations lower values were observed. Data for 14C activity in the atmospheric CO2 in Zagreb are available for period 1985 – 2016, while data for Plitvice Lakes are not continuous. A systematic decreasing trend of -0.46 ± 0.04 pMC per year is observed for Zagreb atmospheric CO2 in period 1993 – 2016 with seasonal variations superposed on the trend. The winter minima in atmospheric 14CO2 activity are systematically lower than 100 pMC, probably due to the contribution of fossil fuel combustion in the city area. Systematic and continuous monitoring 14C activity in atmospheric CO2 and biological samples (mostly apples, vegetable, cereals, corn) in the vicinity of the Nuclear Power Plant Krško (NEK) in Slovenia has been performed since 2006. The 14C activity of atmospheric CO2 at two locations inside the NEK area is on the average slightly higher than that in Zagreb. It depends on the 14C activity released in air-born effluent. The influence of the 14C releases has been observed also in plants. Higher 14C activity in plants is most pronounced shortly after spring refuelling, when plants use atmospheric CO2 that contains 14C released from NEK. The influence of the released air-born 14C activity is measurable in both atmospheric CO2 and in plants ; the higher the activity of gaseous effluent, the higher the atmospheric and plant 14C activity. However, the influence is temporally and spatially limited. Average 14C activity in plants at the control location Dobova does not differ from the average atmospheric 14C activity in Zagreb.

3H ; 14C ; environment ; atmosphere

Id-55, invited talk