Contribution of close-in fallout from the French atmospheric tests in inventories of 137Cs, 241Am and plutonium (238, 239, 240) in Gambier Islands (French Polynesia) - Signatures of stratospheric fallout in the Southern Hemisphere.

The inventories of 137Cs (503 ±â€¯34 Bq.m-2), 241Am (11.3 ±â€¯1.2 Bq.m-2), 241Pu (33.7 ±â€¯3.4 Bq.m-2), 238Pu (6.82 ±â€¯0.87 Bq.m-2) and 239+240Pu (113.0 ±â€¯5.9 Bq.m-2), sum of 239Pu (100 ±â€¯11 Bq.m-2) and 240Pu (14.5 ±â€¯1.7 Bq.m-2), in the Gambier archipelago (23°S) of the French Polynesia, are well higher the global fallout at this latitude, in unequal proportions for the different radionuclides. (240Pu/239Pu)AR (AR: atomic ratio) of 0.0394 ±â€¯0.0062, and (241Pu/239Pu)AR of (2.03 ±â€¯0.39)10-4, confirm that the overwhelmingly dominant source of these radionuclides comes from local fallout during the 1970s of the French atmospheric tests of Moruroa and Fangataufa located nearly 400 km from Gambier. The signatures of the local fallout were deduced from the excess of its inventory in 137Cs and from the mixing lines established from the signatures of the global fallout, some of the test sites and the isotopic ratios measured in Gambier. Signatures obtained are 2.0 ±â€¯0.4 for 137Cs/239+240Pu, 0.045 ±â€¯0.008 for 238Pu/239+240Pu, 0.031 ±â€¯0.009 for 241Am/239+240Pu, 0.092 ±â€¯0.027 for 241Pu/239+240Pu, 0.0163 ±â€¯0.0049 for (240Pu/239Pu)AR, (0.78 ±â€¯0.23)10-4 for (241Pu/239Pu)AR. The concordance of the mixing lines of the [(240Pu/239Pu)AR, (241Pu/239Pu)AR] and the linear regression of these ratios measured in the stratosphere (40°S) during the 1970s, indicates that the signatures of the close-in deposition are also those of the stratospheric injections of the French tests. The signatures of stratospheric fallout in the Southern Hemisphere were evaluated by considering that the fission energy of these injections represents 11% and that of the Northern Hemisphere represents 89% and that the isotopic ratios of stratospheric injections remained the same over the period 1970-1974. The activity ratios deducted are 21.9 ±â€¯0.1 in 137Cs/239+240Pu, 0.11 ±â€¯0.05 in 238Pu/239+240Pu, 1.03 ±â€¯0.12 in 241Pu/239+240Pu and 0.35 ±â€¯0.04 in 241Am/239+240Pu. The associated atom ratios are 0.157 ±â€¯0.011 for (240Pu/239Pu)AR and (8.33 ±â€¯0.48)10-4 for (241Pu/239Pu)AR. These signatures appear to be consistent with the results of the inventories at Hiva Oa, located more than 1,000 km north of both French test sites, and with those found in the Australian continent, in regions not impacted by UK-test debris. The proportions of close-in tropospheric fallout from the French tests are about 90% in Gambier. They represent a proportion in the inventories of 40% for the 137Cs, 60% for 241Am and in the range between 80 and 90% for Pu isotopes.

Environmental consequences of uranium atmospheric releases from fuel cycle facility: II. The atmospheric deposition of uranium and thorium on plants.

Uranium and thorium isotopes were measured in cypress leaves, wheat grains and lettuce taken in the surroundings of the uranium conversion facility of Malvési (South of France). The comparison of activity levels and activity ratios (namely (238)U/(232)Th and (230)Th/(232)Th) in plants with those in aerosols taken at this site and plants taken far from it shows that aerosols emitted by the nuclear site (uranium releases in the atmosphere by stacks and (230)Th-rich particles emitted from artificial ponds collecting radioactive waste mud) accounts for the high activities recorded in the plant samples close to the site. The atmospheric deposition process onto the plants appears to be the dominant process in plant contamination. Dry deposition velocities of airborne uranium and thorium were measured as 4.6 × 10(-3) and 5.0 × 10(-3) m s(-1), respectively.