First measurements of chlorine 36 (36Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France

Abstract

Chlorine 36 (36Cl) is a radionuclide of natural and anthropogenic origin, mainly used as a tracer in geochemical studies. Owing to analytical constraints and its low environmental levels, knowledge of 36Cl behavior in the environment is still very limited. In this study, we use environmental measurements to report for the first time the wet deposition fluxes of 36Cl downwind an anthropogenic source, the Orano nuclear reprocessing plant, which chronically emits 36Cl into the environment. Measurements of 36Cl in rainwater samples at our study site were 1–2 orders of magnitude above the environmental background. The isotope ratios 36Cl/Cl of the samples and the 36Cl content in the rainwater averaged 2.3x10−12 at at−1 and 1.7x108 at l−1 respectively. A decrease in these levels was observed 20 km away from the study site, outside the plant's gas plume, indicating that the marking of 36Cl on the study site is related to the plant discharges. Over the sampling period, wet deposition fluxes at the study site averaged 3.4x103 at m−2s−1, with significant values measured when precipitations scavenge the plant's gas plume down onto our study site. Analysis of these fluxes also revealed the presence of a significant rainout phenomenon in the study area. These results provide new data on the wet deposition flux of 36Cl and will thus enable better assessment of impact studies in a context of decommissioning or accidents involving nuclear power plants.