[en] Full text: Specific activities of ¹⁴C were measured in grass samples collected up to 5km from the Brazilian nuclear power reactors. Sampling was performed in 2004 and 2005 and took into account different wind directions. The measurements were made by single stage accelerator mass spectrometry (SSAMS) at Lund University, Sweden. The ¹⁴C measurements varied between 227 and 299 Bq/kgC. Half of the samples showed background specific activities, while the other samples presented ¹⁴C excess varying between 1 to 18%. The exceptions are two samples that showed ¹⁴C specific activities 22% higher than background value. These high values were found close to the power plants and along the main wind directions (NE and NNE). The unexpected higher ¹⁴C excess found in these samples can be related to the local hilly topography that may have favoured the ¹⁴C accumulation in the sampled area. Preliminary data suggest that ¹⁴C dispersion follow a Gaussian plume model, which still needs to be confirmed by employing long-term sampling and, simultaneously, measurements of ¹⁴C of the source and of the ambient air. In conclusion, there is a clear anthropogenic ¹⁴C signal recorded by grass around the Brazilian nuclear power plants. The highest values were found NE and NNE of the power plants, which are the main wind direction in the area. (author)