The VATO project: An original methodology to study the transfer of tritium as HT and HTO in grassland ecosystem
Résumé
Tritium (3H) is mainly released into the environment by nuclear power plants, military nuclear facilities
and nuclear reprocessing plants. The construction of new nuclear facilities in the world as well as the
evolution 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 atmospheric
source (currently releasing HT and HTO) to a grassland ecosystem. A fully instrumented
technical platform with specifically designed materials was set up downwind of the AREVA NC La Hague
reprocessing plant (Northwest of the France). This study, started in 2013, was conducted in four main
steps to provide an hourly data set of 3H concentrations in the environment, adequate to develop and/or
validate transfer models. It consisted first in characterizing the physico-chemical forms of 3H present in
the air around the plant. Then, 3H transfer kinetics to grass were quantified regarding contributions from
various compartments of the environment. For this purpose, an original experimental procedure was
provided to take account for biases due to rehydration of freeze-dried samples for the determination of
OBT activity concentrations in biological samples. In a third step, the 3H concentrations measured in the
air and in rainwater were reconstructed at hourly intervals. Finally, a data processing technique was used
to determine the biological half-lives of OBT in grass.