The VATO project: An original methodology to study the transfer oftritium as HT and HTO in grassland ecosystem

International audienceTritium (3H) is mainly released into the environment by nuclear power plants, military nuclear facilitiesand nuclear reprocessing plants. The construction of new nuclear facilities in the world as well as theevolution of nuclear fuel management might lead to an increase of 3H discharges from the nuclear industry.The VATO project was set up by IRSN (Institut de Radioprotection et de Sûrete Nucleaire) and EDF(Electricite de France) to reduce the uncertainties in the knowledge about transfers of 3H from an atmosphericsource (currently releasing HT and HTO) to a grassland ecosystem. A fully instrumentedtechnical platform with specifically designed materials was set up downwind of the AREVA NC La Haguereprocessing plant (Northwest of the France). This study, started in 2013, was conducted in four mainsteps to provide an hourly data set of 3H concentrations in the environment, adequate to develop and/orvalidate transfer models. It consisted first in characterizing the physico-chemical forms of 3H present inthe air around the plant. Then, 3H transfer kinetics to grass were quantified regarding contributions fromvarious compartments of the environment. For this purpose, an original experimental procedure wasprovided to take account for biases due to rehydration of freeze-dried samples for the determination ofOBT activity concentrations in biological samples. In a third step, the 3H concentrations measured in theair and in rainwater were reconstructed at hourly intervals. Finally, a data processing technique was usedto determine the biological half-lives of OBT in grass