Empirical calibration of uranium releases in the terrestrial environment of nuclear fuel cycle facilities

In the present paper the activity of uranium isotopes measured in plants and aerosols taken downwind of the releases of three nuclear fuel settlements was compared between them and with the activity measured at remote sites. An enhancement of ²³⁸U activity as well as ²³⁵U/²³⁸U anomalies and ²³⁶U are noticeable in wheat, grass, tree leaves and aerosols taken at the edge of nuclear fuel settlements, which show the influence of uranium chronic releases. Further plants taken at the edge of the studied sites and a few published data acquired in the same experimental conditions show that the ²³⁸U activity in plants is influenced by the intensity of the U atmospheric releases. Assuming that ²³⁸U in plant is proportional to the intensity of the releases, we proposed empirical relationships which allow to characterize the chronic releases on the ground. Other sources of U contamination in plants such as accidental releases and "delayed source" of uranium in soil are also discussed in the light of uranium isotopes signatures.