Situation of the surveillance of radioactivity in French Polynesia in 2007. Results of the I.R.S.N. 's surveillance network

The 543 atmospheric nuclear tests released radionuclides that have deposited themselves throughout the world. The Environmental Study and Surveillance Laboratory, 'Laboratoire d etude et de suivi de l'environnement' (L.E.S.E.) of the Institute of nuclear safety and radiation protection (I.R.S.N.), takes part, for more than 35 years, in the evaluation of the dosimetric consequences of these atmospheric depositions, especially those originating with the 41 tests realized in the territory of French polynesia from 1966 to 1974. This laboratory is established in Tahiti. The actualized dosimetric evaluation due to the foodstuff ingestion requires to collect the most representative samples of the feed ration of the Polynesians living in the 5 archipelagoes of this territory. These samples belong to the marine environment of full sea, the lagoon environment and the terrestrial environment. Certain samples of the physical environment are also taken (air, water). 355 samples collected in 2007 are measured by Hp-Ge low background gamma spectrometry in order to be able to characterize lowest possible radioactivity levels. The levels of activity of Pu isotopes and 90Sr are also given for 50 selected samples and tritium activities for 20 water samples. After a period of regular decay of radioactivity after the stop, in 1974, of the French atmospheric tests, the radiological state observed in the year 2007 is the same of that of the recent previous years, at a very low level. for example, the 137Cs rate in the polynesian air is ten times lower than the parisian rate. In fact, the residual radioactivity essentially relates to 137Cs, the only artificial radionuclide still measurable in the archipelago. In term of additional dose, this artificial and residual radioactivity is lower than 6 μSv by year. this value corresponds to less than 1% of exposure due to natural radioactivity in Polynesia (approximately 1 milli Sv). (N.C.)