Advanced atmospheric ¹⁴C monitoring around the Paks Nuclear Power Plant, Hungary

Atmospheric air samples were collected at 9 monitoring stations (A1 to A9) less than 2 km from the Paks Nuclear Power Plant (Paks NPP) and a background station (B24). The monthly integrated CO₂ and total carbon (CO₂+hydrocarbons (C_nH_m)) samples were collected to determine the excess ¹⁴C activity at the vicinity of the NPP. The measurements providing the ¹⁴C/¹²C ratio of the monthly integrated samples were carried out on a MICADAS type AMS at HEKAL. Due to the relatively low ¹⁴CO₂ emission of PWR type Paks reactors and the local Suess effect, there was negligible excess ¹⁴C activity at the investigated stations in the pure CO₂ fraction during the investigated 2 years period (2015-2016). On the contrary, there was a detectable (although minor) excess at every station in the C_nH_m fraction. In case of CO₂, the average Δ¹⁴C excess was 3.8‰ and the highest measured value was 91.2‰ at the A3 station in February 2015. In case of C_nH_m, the average excess was 31.1‰ and the highest measured value was 319.1‰ at the A4 station in February 2016. We applied PC-CREAM 08 modelling to investigate the observed excess ¹⁴C activity at the environmental sampling stations, which depends on the distance from the NPP and the meteorological conditions, such as wind direction and wind speed. Meteorology data was collected at the operating area of the Paks NPP in a meteorology tower. The direct C-14 emission through the 120 m high stacks was measured in the NPP by liquid scintillation counting. These emission data and our model calculations explain the excess activity in the C_nH_m fraction at the A4 station, which is located only 915 m far from the NPP's stacks in the prevailing wind direction. The excess activity at A3 station (the farthest unit) probably came from the nearby NPP wastewater discharge point. The recently observed average excess and highest excess data is similar to the published data in former studies (Molnár et al., 2007; Veres et al., 1995) on Paks NPP, the highest ¹⁴CO₂ and ¹⁴C_nH_m excess are just a little higher than it was in the earlier studies, but in these former studies, the A3 station was not equipped with a radiocarbon monitoring unit and the level of radiocarbon emission was almost invisible from the wastewater discharge point.