129I/127I ratio measurements in bovine thyroids from the North Cotentin area (France)

Iodine-129 is routinely released in the gaseous and liquid low-level radioactive effluents of nuclear spent fuel reprocessing plants. Environmental impact assessment of these discharges are performed based on monitoring samples of different types of natural indicators. Thyroid is considered as a relevant organ to monitor radioactive iodine isotopes. In this study, bovine thyroids were collected in herds located in the Cotentin area under the influence of authorized low level gaseous effluents of the La Hague nuclear fuel-reprocessing plant. For low level 129I/127I ratios, characteristic of environmental samples (10−12 to 10−7), RNAA or SMA that includes important radiochemical preparation steps are used. This paper demonstrates the interest of direct γ-X spectrometry to measure 129I activities, associated to INAA to measure 127I to attain higher ratios levels (10−6 to 10−4). This study shows the interest of monitoring bovine thyroids considered as sentinel organs to characterize the dispersion in space and time of 129I discharged in low level radioactive gaseous effluents by the La Hague reprocessing plant.