Study on transfers of uranium, thorium and decay products from grain, water and soil to chicken meat and egg contents.

Activity concentrations of the uranium and thorium series radionuclides were determined in chicken meat and eggs as well as in soil, water and other dietary intakes of poultry at five sites of the French territory. These data allow the calculation of transfer coefficients which enrich the database given by the technical report series no. 472 of the IAEA. In egg contents, the highest activity concentrations (in mBq kg(-1) fresh weight) are for (226)Ra, ranging between 136 and 190 and are much lower for uranium (between 0.51 and 1.30 for (238)U). In chicken meat, (238)U activity concentration is higher than in egg contents and ranges between 1.7 and 9.7. Concerning (232)Th, its activity concentration is lower than uranium and ranges between 0.5 and 4.9. Daily ingested activity concentration by the animals was assessed taking into account the activity concentrations measured in the grains, in the soil and in the drinking water. The activity concentration in grains and the daily intakes allow the calculation of concentration ratios and transfer coefficients for chicken meat and egg contents. In chicken meat the transfer coefficients (d kg(-1)) range between 0.0018 and 0.0073 for (238)U and between 0.0008 and 0.0028 for (232)Th. In egg contents they range from 0.00018 to 0.0018 for (238)U and are much higher for radium isotopes (0.10-0.23 for (226)Ra and 0.07-0.11 for (228)Ra).

Potential sources affecting the activity concentrations of 238U, 235U, 232Th and some decay products in lettuce and wheat samples.

The activity concentrations of radionuclides within the uranium and thorium series were determined in wheat and lettuce at five sites in France, and in their respective potential sources: crop soils of wheat and crop soils and irrigation waters of lettuce. These data were used to calculate concentration ratios and to enrich the database supported by the technical report series N°472 of the IAEA (2010). For wheat and lettuce, the activity concentrations were in the same range for all radionuclides studied, except for (210)Pb, which had higher activity concentrations in wheat, ranging between 1.3 and 11 Bq kg(−1) (fresh weight) as compared to 0.4 and 0.7 Bq kg(−1) (fresh weight) for lettuce. For wheat, the range of activity concentrations (mBq kg(−1); fresh weight) decreased as (210)Pb > (226)Ra (56­1511) ≈ (228)Ra (86­769) > (228)Th (19­176) ≈ (238)U (11­169) ≈ (234)U (12­150) ≈ (230)Th (9.08­197.18) ≈ (232)Th (8.61­121.45) > (235)U (0.53­7.9). For lettuce, it decreased as (228)Ra (<320­1221) > (210)Pb (409­746) > (226)Ra (30­599) ≈ (228)Th (<29­347) > (238)U (8­120) ≈ (234)U (8­121) ≈ (230)Th (5.21­134.63) ≈ (232)Th (5.25­156.99) > (235)U (0.35­5.63). The species differences may reflect different plant physiologies. Through the study of activity ratios of wheat and lettuce in relation with those of the various radionuclide sources it has been possible to highlight the contribution of the main sources of natural radionuclides. Indeed, irrigation water when the uranium concentration is enhanced (>30 mBq L(−1)) contributed significantly to the activity concentration of uranium in lettuces. Concerning the high activity concentrations of (210)Pb, it could be explained by atmospheric particle deposition. The effect of soil particles resuspension and their adhesion to the plant surface seemed to be important in some cases. The soil-to-plant transfer factors were calculated for lettuce and wheat. The values were lower in wheat than in lettuce except for (210)Pb which had similar values in the two species (0.11­0.13 respectively). For both species, (210)Pb followed by (228)Ra (0.015­0.10) and (226)Ra (0.010­0.051) displayed the highest transfer factor, whereas (238)U had intermediate values (0.0015­0.030) and (232)Th exhibited the lowest (0.0014­0.013).

Actinides and decay products in selected produce and bioindicators in the vicinity of a uranium plant.

Cypress needles collected at the edge of the Malvési uranium facility (SW France) exhibit enhanced activities of actinides and some decay products (uranium, americium, plutonium, (230)Th, (226)Ra) compared to a remote site. These enhanced activities resulted from the release of U via smokestacks and passive release from former artificial ponds located inside the nuclear site. Enhanced activities are also observed in selected produce (wheat, lettuce, fruits) sampled from the edge of the site. However, excess actinides measured in wheat grains in 2007 are inconsistent with the activities and the uranium ratio measured in the soils. This result suggests that the studied annual crops were contaminated mainly through the short-term release of airborne actinides, and that other transfer pathways, such as, uptake through the roots or adhesion of soil particles, were negligible.

Specific activity to H*(10) conversion coefficients for in situ gamma spectrometry.

The typical situations found in in situ gamma spectrometry have been simulated by Monte Carlo techniques to obtain the energy spectra of the photon fluence rate existing at 1 m above ground. The main difficulty found with the model is its slow convergence. A method to speed up the calculation has been derived. The results of the model have been thoroughly tested against existing data. In a final stage, the specific activity to H*(10) conversion coefficients have been derived for the typical scenarios encountered in the in situ gamma spectrometry.

Leda: A gamma-gamma coincidence spectrometer for the measurement of environment samples.

This paper presents a new gamma-gamma coincidence spectrometer to measure the radioactivity in environmental samples. This system, called Leda, is made of 2 HPGe and 1 NaI(Tl). The different analysis channels (single, in coincidence or in anti-coincidence) possible thanks to the digital electronics are described. Results obtained with environmental samples are shown. Despite its low efficiency, this method improves the detection limits for all emitters due to its very low background, and thus decreases the counting time.

Low level measurement of (60)Co by gamma ray spectrometry using γ-γ coincidence.

This paper presents the latest development of the laboratory to measure the natural and artificial massic activities in environmental samples. The measurement method of coincident emitters by gamma-gamma coincidence using an anti-Compton device and its digital electronics is described. Results obtained with environmental samples are shown. Despite its low efficiency, this method decreases detection limits of (60)Co for certain samples compared to conventional gamma-ray spectrometry due to its very low background.

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.

Uranium decay daughters from isolated mines: Accumulation and sources.

This study combines in situ gamma spectrometry performed at different scales, in order to accurately locate the contamination pools, to identify the concerned radionuclides and to determine the distribution of the contaminants from soil to bearing phase scale. The potential mobility of several radionuclides is also evaluated using sequential extraction. Using this procedure, an accumulation area located downstream of a former French uranium mine and concentrating a significant fraction of radioactivity is highlighted. We report disequilibria in the U-decay chains, which are likely related to the processes implemented on the mining area. Coupling of mineralogical analyzes with sequential extraction allow us to highlight the presence of barium sulfate, which may be the carrier of the Ra-226 activities found in the residual phase (Ba(Ra)SO4). In contrast, uranium is essentially in the reducible fraction and potentially trapped in clay-iron coatings located on the surface of minerals.

Fission product activity ratios measured at trace level over France during the Fukushima accident.

The nuclear accident of Fukushima Dai-ichi (Japan) which occurred after the tsunami that impacted the northeast coasts of Japan on March 11th, 2011 led to significant releases of radionuclides into the atmosphere and resulted in the detection of those radionuclides at a global scale. In order to track airborne radionuclides from the damaged reactors and to survey their potential impact on the French territory, the French Institute of Radiation Protection and Nuclear Safety (Institut de Radioprotection et de Sureté Nucléaire IRSN) set up an enhanced surveillance system to give quick results as needed and later give quality trace level measurements. Radionuclides usually measured at trace levels such as (137)Cs and in a very sporadic way (131)I were reported. Radionuclides that we had never measured in air since the Chernobyl accident: (134)Cs, (136)Cs, the mother/daughter pairs (129m)Te-(129)Te and (132)Te-(132)I, and (140)La (from the mother-daughter pair (140)Ba- (140)La) were also reported. Except the (131)I/(137)Cs ratio, activity concentration ratios were constant. These ratios could be used to help source term assessment, or as data for transfer studies realized after the passage of contaminated air masses, typically using the (134)Cs/(137)Cs ratio.