Distribution of 14C in the atmosphere and biological samples around the Nuclear Power Plant Krško in Slovenia

Human activities disturbed the natural 14C distribution in the atmosphere in the last half of the 20th century. Besides the big amounts of 14C released by nuclear bomb tests it is produced also by nuclear power plants and in form of 14CO2 enters the carbon cycle contributing through food chain to the dose of the local population. The aim of this study was to determine distribution of 14C in a close vicinity of the Nuclear Power Plant Krško (NEK) in Slovenia, and to estimate possible contribution of NEK to the effective dose. Atmospheric CO2 was collected since 2006 on a monthly basis 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 and measured in LSC Quantulus 1220. Sampling campaigns of biological samples (apples, corn, cereals, grass) were performed twice a year and sampling sites were chosen in the immediate vicinity and in the wider environment of the NEK smokestack, and at a control site 10 km away. 14C activity was measured in LSC by direct absorption method. 14C activity of the atmospheric CO2 at site A inside NEK showed no observable deviation from 14C activities at clean-air sites, but that at site B was slightly higher, because lies in the dominant wind direction. However, significantly higher 14C activities were measured at both sites during the period of regular maintenance of the reactor in Oct 2007 and April 2009. 14C activities in biological samples around NEK showed slightly higher 14C activities than at the control site, and depend on the distance and on the most pronounced wind direction. Higher 14C activities were recorded in periods following the maintenance of NEK and can be explained by an order of magnitude higher discharge of 14C from the smokestack. An estimate of the effective dose received by ingestion of food (fruits and vegetables) grown in the vicinity of NEK results in the contribution of NEK to the natural dose of less than 1 uSv.