Deuterium- und $^{18}$O-Gehalt im Kühlwasser von Kraftwerkskühltürmen

Abstract

Deuterium- and $^{18}$O-content in the Cooling Water of Power Station Cooling Towers. The O-18/O-16 and D/H isotope ratios of water from two different cooling towers were determined by mass spectrometry. The observed isotope fractionation corresponds to that known from natural evaporation or transpiration processes:Cooling tower I: $\delta$(D) = 46.8 $^\circ$/$_{\circ}$$_{\circ}$ , 6($^{18}$O ) = 7.6 $^\circ$/$_{\circ}$$_{\circ}$ Cooling tower II: $\delta$(D) = 33.9 $^\circ$/$_{\circ}$$_{\circ}$, $\delta$($^{18}$O) = 5.7 $^\circ$/$_{\circ}$$_{\circ}$ Evaluation of simple compartment models of a cooling tower and a distillation device suggests that there exists some isotope discrimination within the open trickling unit of a cooling tower analogous to that in a rectification column. In areal coolingtower, however, this effect is compensated largely by the recycling of the cooling water, resulting only in a small enrichment of the heavy isotopes. This can be understood as the result of three partial effects: (I) a fractionation in the vapor pressure equilibrium, (II) a kinetic effect due to diffusion of the water vapor into a turbulent atmosphere, and (III) an exchange effect which is proportional to relative humidity. This low enrichment of the heavy isotope excludes the technical use of cooling towers as isotope separation devices