14C in biological samples and in the atmosphere around nuclear power plant Krsko (NEK) in Slovenia

Full text: Nuclear power plants represent a small source of carbon 14C that enters the carbon cycle together with the 14C produced naturally in the atmosphere. The present-day natural 14C distribution can be slightly disturbed in the close vicinity of the power plants. In this paper we report on monitoring of 14C in the atmospheric CO2 and in biological material in the close environment of nuclear power plant Krsko (NEK) in Slovenia. Based on the regulation, sampling campaigns of biological samples (apples, corn, cereals, grass) were performed twice a year during 2006 and 2007. Sampling sites were chosen in the immediate vicinity (250 m - 700 m from the plant) and in the wider environment (1000 m - 1500 m) of the plant, as well as at a control site 10 km away. Carbon 14C activity was measured by direct absorption method in LSC Quantulus 1220. Atmospheric CO2 was collected at two locations (A and B) inside the NEK area by absorption of CO2 in saturated NaOH. The CO2 recovered from the carbonate was used for benzene synthesis. Most of the locations in the immediate vicinity of NEK showed slightly higher 14C activities than the control site. Spatial distribution of 14C activities around NEK showed the dependence on the distance and on the direction. In all campaigns the highest activities were obtained at the locations that coincided with the most pronounced wind directions. 14C activity of the atmospheric CO2 at site A inside NEK showed no observable deviation from natural 14C activities, while it was always slightly higher at site B that lies in the dominant wind direction. However, higher 14C activities were detected at both sites during the refuelling outage periods. Based on the measurements, an accurate assessment of the effective dose to the public can be obtained. The dose received by ingestion of food (fruits and vegetables) grown in the vicinity of the Krsko nuclear power plant results in the contribution to the dose of most exposed individual of less than 1 μSv. (author)