14C content in vegetation in the vicinities of Brazilian nuclear power reactors

14C specific activities were measured in grass samples collected around Brazilian nuclear power reactors. The specific activity values varied between 227 and 299 Bq/kg C. Except for two samples which showed 14C specific activities 22% above background values, half of the samples showed background specific activities, and the other half had a 14C excess of 1–18%. The highest specific activities were found close to the nuclear power plants and along the main wind directions (NE and NNE). The activity values were found to decrease with increasing distance from the reactors. The unexpectedly high 14C excess values found in two samples were related to the local topography, which favors 14C accumulation and limits the dispersion of the plume. The results indicate a clear 14C anthropogenic signal within 5 km around the nuclear power plants which is most prominent along northeastwards, the prevailing wind direction.