~(14)Co_2 dispersion around two PWR nuclear power plants in Brazil

摘要

Atmospheric air samples were taken within 3 km from power plants encompassing five different distances and wind directions. Samples were taken between 2002 and 2005 aiming to evaluate the environmental ~(14)C enrichment due to the operation of Brazilian nuclear power plants. The sampling system consisted of a pump connected to a trapping column filled with a 3 M NaOH solution. The trapped CO_2 was analyzed for ~(14)C by using a single stage accelerator mass spectrometry (SSAMS). All sampling sites revealed measurable ~(14)C excess values. The maximum excesses were of 15 and 14 mBq/ m~3 for sampling sites placed at NE of the power plants, which is the main wind direction in the area. The mean excesses values were 12 mBq/m~3 to the NE direction, 8 mBq/m~3 to the E, 10 mBq/m~3 to the N, 8 mBq/m~3 to the WNW and 7 mBq/m~~3 to the W direction (increasing distances from NE to W). Compared to other Light Water Reactors (LWR) data, these means' values are significantly higher than the average worldwide reported value of 3 mBq/m~3. Available data indicate that the observed values are not related to ~(14)C emission by the power plants vent stack.rnOther factors, such as topography, seem to have an important role because it affects wind dispersion thus favoring ~(14)C accumulation in the sampled area. Moreover, the high elevations around the power plants enhance the chances to measure high values of ~(14)C since the plume can be intercepted before it is drawn to the ground. Modeling of the plume has shown that its dispersion does not follow a Gaussian model and that agreement between atmospheric CO_2 and vegetation ~(14)C activities occurs only for sampling sites placed at NE of the power plants.