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1.
The concentrations of 238Pu, 239,240Pu, 241Am and 244Cm were determined in sediment samples from five streams and two ponds on the Savannah River Plant (SRP) and in four sediment samples from the Savannah River above and below the plant site. The following concentration ranges were determined: 238Pu, 0·07–386 fCi g−1; 239,240Pu, 0·37–1410 fCi g−1; 241Am, 0·1–4360 fCi g−1; 244Cm, <0·01–392 fCi g−1. Comparisons of the elemental and isotopic ratios of the sediments show that the majority of the sediments studied have been impacted upon by plant operations and that sediments outside the plant boundary in the Savannah River have only been influenced by aerial releases. Atom ratios of 240Pu/239Pu indicate that up to 86% of the Pu in these sediments is derived from plant operations. However, comparisons of the concentration data with values for other impacted sediments near nuclear facilities indicate that the levels are relatively small. Finally, <13% of the Pu, Am or Cm in pond sediments is associated with humic or fulvic acids, indicating that little of the material should be remobilized in oxic environments through organic complexation.  相似文献   

2.
A large thorium ore deposit is located in Morro do Ferro, a hill in the Poços de Caldas Plateau, Minas Gerais, Brazil, which contains an estimated 30 000 t of Th and 100 t of U in a highly weathered matrix exposed to erosion and leaching. 228Ra and 226Ra were analyzed in surface waters collected at various points in the drainage basin and in groundwaters from wells drilled through and around the ore body. The concentrations in groundwater demonstrated that radium is markedly leached by rainwater percolating through the ore body. In its transit underground, radium is removed from groundwater by sorption on soil particles and this natural process greatly reduces the radium discharged to the environment. In dry weather, the concentration of dissolved 228Ra in the main stream draining the Morro do Ferro is 7·0 ± 1·1 mBq litre−1 and in a control stream 1·6 ± 0·3 mBq litre−1. The estimated 228Ra mobilization rate by solubilizations is of the order of 10−7 y−1.  相似文献   

3.
Tritium occurs in nature in trace amounts, but its concentration is changing due to natural and artificial sources. Studies focusing on natural tritium have to take into account the effect of artificial sources. Also, the impact of tritium is an important issue in environmental protection, e.g. in connection with the emissions from nuclear power plants. The present work focuses on the rain washout of tritium emitted from the Paks nuclear power plant in Hungary. Rainwater collectors were placed around the plant and after a period of precipitation, rainwater was collected and analysed for tritium content. Samples were analysed using low-level liquid scintillation counting, with some also subject to the more accurate 3He ingrowth method. The results clearly show the trace of the tritium plume emitted from the plant; however, values are only about one order of magnitude higher than environmental background levels. A washout model was devised to estimate the distribution of tritium around the plant. The model gives slightly higher concentrations than those measured in the field, but in general the agreement is satisfactory. The modelled values demonstrate that the effect of the plant on rainwater tritium levels is negligible over a distance of some kilometres.  相似文献   

4.
Uptake and clearance of radionuclides in foodstuffs have been studied in the neighbourhood of Aberdeen in North East Scotland following the Chernobyl accident. The level of131 I in goats' milk was 100–200 Bq litre−1 in early May and declined with an effective half-life of 4sd3 days, but that in cows' milk was only a few Bq litre−1 as most cattle were kept indoors. 137Cs and 103Ru activities in broccoli declined with effective half-lives of 11 and 6 days respectectively, while 137Cs in grass decresed with a half-life of 22 days, the reduction appearing to show a relationship to weekly rainfall. Studies of tissues from groups of lambs initially grazed on contaminated pasture and later (a) fed indoors on concentrates or (b) continuing to graze outdoors, showed the 137Cs concentrations to decline with half-lives of (a) 17 days and (b) 25 days, while the half-lives describing the reduction in total 137Cs activity were (a) 20 days and (b) 35 days.  相似文献   

5.
The aims of the present research are to describe the uptake of 99Tc by trees intercepting contaminated groundwater from a radioactive waste storage site, to identify the major 99Tc pools within the woodland ecosystem and to assess the relative mobility of 99Tc in the existing element cycle. Technetium in the groundwater freely passed through a dialysis membrane with a molecular weight exclusion limit of approximately 3500 amu and 99Tc in the groundwater chromatographed on Biogel P-2 in a manner similar to pertechnetate anion (TcO4). Reducing conditions and organic associations at the study site were probably responsible for the relatively large amount (83–92%) of the 99Tc that was nonextractable from soil by 0·01 m CaCl2. More than one-third of the 99Tc was released from the soil by oxidizing reagents, indicating the presence of chemically reduced forms. The highest average 99Tc concentrations in vegetation were found in herbaceous plants (18 530 pCi g−1 dry wt). Although 99Tc was progressively accumulated over the growing season in tree leaves, average concentrations in tree wood and twigs were equal to or greater than concentrations in leaves. Tree wood was the major above-ground pool for 99Tc because of the high concentrations in wood as well as the large amount of wood relative to other biomass at the site. Technetium was not easily leached from the trees by rainfall and was not readily extractable from forest floor leaf litter by water. The relative importance of return pathways for 99Tc to the forest floor was leaf fall>stemflow >throughfall, indicating that 99Tc was conserved by the trees. Snails and millipedes from the leaf litter layer concentrated technetium 20- and 16-fold, respectively, above levels found in the soil. Pertechnetate was rendered less bioavailable after ingestion by a leaf litter macroinvertebrate (Porcellio sp.) common to the study site.  相似文献   

6.
This paper deals with the physico-chemical behaviour of neptunium in sea water and with its capacity for transfer to coastal or deep-sea sediments and for uptake by two benthic species, Arenicola marina (L.) and Cerastoderma edule (L.). We used the 239Np isotope with mass concentrations in sea water of about 2·5 × 10−10−5·4×10−12 g litre−1, which are close to the concentrations observed in the environment for 237Np. The experimental results show that Np occurs in solution mainly as the neptunyl ion NpO2+, but soluble anionic and neutral complexes and particulate forms were also detected. The distribution coefficients for the sediments varied from 350 to 6500. The carbonate phase plays a decisive role in neptunium transfer but other fixation processes are also possible. Concentration factors after 13 days were found to have values of 40 and 14 for the shells and soft parts of cockles, respectively, while polychaetes had a concentration factor of 2. Thus Np has a smaller probability of transfer to sediments and organisms than have plutonium and americium.  相似文献   

7.
This study aimed at obtaining background tritium concentrations in precipitation and air at Rokkasho where the first commercial spent nuclear fuel reprocessing plant in Japan has been under construction. Tritium concentration in monthly precipitation during fiscal years 2001-2005 had a seasonal variation pattern which was high in spring and low in summer. The tritium concentration was higher than that observed at Chiba City as a whole. The seasonal peak concentration at Rokkasho was generally higher than that at Chiba City, while the baseline concentrations of both were similar. The reason for the difference may be the effect of air mass from the Asian continent which is considered to have high tritium concentration. Atmospheric tritium was operationally separated into HTO, HT and hydrocarbon (CH3T) fractions, and the samples collected every 3 d-14 d during fiscal year 2005 were analyzed for these fractions. The HTO concentration as radioactivity in water correlated well with that in the precipitation samples. The HT concentration was the highest among the chemical forms analyzed, followed by the HTO and CH3T concentrations. The HT and CH3T concentrations did not have clear seasonal variation patterns. The HT concentration followed the decline previously reported by Mason and Östlund with an apparent half-life of 4.8 y. The apparent and environmental half-lives of CH3T were estimated as 9.2 y and 36.5 y, respectively, by combining the present data with literature data. The Intergovernmental Panel on Climate Change used the atmospheric lifetime of 12 y for CH4 to estimate global warming in its 2007 report. The longer environmental half-life of CH3T suggested its supply from other sources than past nuclear weapon testing in the atmosphere.  相似文献   

8.
222Rn released by mature tall fescue (Festuca arundinacea Schreb.) growing on uranium mill wastes in a controlled environment was a direct function of leaf area and essentially unrelated to the quantity of water transpired by the plants. The quantity of 222Rn released by the grass blades at maturity was approximately 0·01 Bq m−2 s−1 (0·3 pCi m−2 s−1). We suggest that the radioactive gas is transported from the rooting medium to leaves by mass flow in liquid water, but from leaves to the atmosphere by a path generally independent of water, i.e., primarily through the leaf cuticle and epicuticular wax.  相似文献   

9.
In the metropolitan New York area, maximum concentrations in air of radioactive aerosol and gaseous debris from the Chernobyl accident of April 1986 were much lower than those measured in Europe. The observed maxima were: for gaseous 131I, 23mBq m−3; for aerosol samples, 20mBq m−3 of 131I and 9·mBq m−3 of 137Cs. The data suggest that little gas-to-particle transformation of iodine occurred during transport of the radioactive cloud from the Ukraine to New York. The ratios of 103Ru and other refractories to 137Cs were low in the first debris sampled, debris which probably was emitted from Chernobyl in late April during the early stages of the accident. In subsequent samples these ratios were higher, presumably because debris from the later, hotter stages of the fire had reached our sampling sites. A significant fraction (25–40%) of the deposition of 131I and 137Cs into our samplers and on grass was by dry deposition. The total deposition of Chernobyl 137Cs in the area was <1% of that already present in the soil from fallout from past nuclear weapon tests. The highest concentration of 131I measured in fresh milk was about 1.5 B1 liter−1, <0.1% of the US action level. The dose to the thyroid of a six-month-old infant who had fresh milk as a sole food source would be about 70 μGy (7 mrad).  相似文献   

10.
The Ob and Yenisey rivers are major contributors to total riverine discharge to the Arctic Ocean. Several large nuclear facilities discharge into these rivers, which could affect actual and potential discharges of radionuclides to the Arctic region. This article presents new radionuclide concentration and grain-size data resulting from analyses of several sediment samples collected during research cruises in the Ob and Yenisey estuaries and adjacent areas during 2000 and 2001. Results indicate that discharges from the main nuclear facilities do not constitute a major contribution to the level of radioactive contamination in the marine areas studied, though Co-60 was detected at low concentrations in some sediment horizons. However, the aggregate contamination from different sources is not radioecologically significant in sediments within the study area, maximum Cs-137 levels being approximately 80 Bq kg(-1) dry weight.  相似文献   

11.
The present study aimed at assessing the activity of natural radionuclides (3H) and hydrochemical parameters (viz., pH, EC, F, NO3, Cl, Ca2+, Mg2+) in the groundwater used for domestic and irrigation purposes in the Varahi and Markandeya river basins to understand the levels of hydrochemical parameters in terms of the relative age(s) of the groundwater contained within the study area. The recorded environmental 3H content in Varahi and Markandeya river basins varied from 1.95 ± 0.25 T.U. to 11.35 ± 0.44 T.U. and 1.49 ± 0.75 T.U. to 9.17 ± 1.13 T.U. respectively. Majority of the samples in Varahi (93.34%) and Markandeya (93.75%) river basins being pre-modern water with modern recharge, significantly influenced by precipitation and river inflowing/sea water intrusion. The EC-Tritium and Tritium-Fluoride plots confirmed the existence of higher total dissolved solids (SEC > 500 μS/cm) and high fluoride (MAC > 1.5 mg/L) in groundwater of Markandeya river basin, attributed to relatively longer residence time of groundwater interacting with rock formations and vice versa in case of Varahi river basin. The tritium-EC and tritium-chloride plots indicated shallow and deep circulating groundwater types in Markandeya river basin and only shallow circulating groundwater type in Varahi river basin. Increasing Mg relative to Ca with decreasing tritium indicated the influence of incongruent dissolution of a dolomite phase. The samples with high nitrate (MAC > 45 mg/L) are waters that are actually mixtures of fresh water (containing very high nitrate, possibly from agricultural fertilizers) and older ‘unpolluted’ waters (containing low nitrate levels), strongly influenced by surface source.  相似文献   

12.
Following the reactor accident at Chernobyl, environmental samples of air, rain water and agricultural and marine products were collected and analyzed by gamma- and alpha-spectrometry. The highest concentrations of 131I in the environmental samples were as follows: 1·0×−1 Bqm−3 (aerosol-associated in air); 3·0×10−1 Bqm−3 (gaseous in air); 2·1×102 bq kg−1 (plants); 1·4×101 Bq litre−1 (milk). Other nuclides such as 95Zr, 95Nb, 103Ru, 106Ru, 125Sb, 129mTe, 132I/132Te, 134Cs, 137Cs, 140Ba/140La, 141Ce and 144Ce were also observed in various environmental samples. 110mAg was only detected in marine products such as cephalopoda and shellfish, 239,240Pu and 241Am originating from the accident were not identified.Based on the monitoring results at one dairy farm, we have derived an equation to model the transport of 131I from pasture grass to milk. This equation was then applied to the data from two other farms around Tokai-Works and the calculated 131I activities in milk were compared with those measured. The equation shows good predictive capabilities for quantification of the peak concentrations of 131I in milk but underestimates longer-term activities.  相似文献   

13.
In order to study the deposition on vegetation of plutonium arising from the testing of nuclear weapons and discharges from nuclear facilities, sheep faeces were collected from the South-west and North of England. The plutonium content of faeces has been shown to be a reproducible and sensitive indicator of deposition on herbage and, with this technique, plutonium discharged from the Sellafield Works of British Nuclear Fuels LImited can be detected 60 km from the site. On moorland pastures the concentration of 239+240Pu in faeces, expressed as activity per gram of ash, is roughly equal numerically to the deposit of plutonium on 1 m2 of vegetation.Some of the plutonium ingested by a grazing sheep is absorbed and the highest concentrations are found in liver. The liver of a sheep grazing on pasture where the 239+240Pu concentration in faeces was about 2 pCi (74 mBq) g−1 of ash, was found to contain <1% of the Generalised Derived Limit for mutton and offal, and the meat <0·001%.  相似文献   

14.
The results of a 21 month sampling program measuring tritium in tree transpirate with respect to local sources are reported. The aim was to assess the potential of tree transpirate to indicate the presence of sub-surface seepage plumes.Transpirate gathered from trees near low-level nuclear waste disposal trenches contained activity concentrations of 3H that were significantly higher (up to ∼700 Bq L−1) than local background levels (0-10 Bq L−1). The effects of the waste source declined rapidly with distance to be at background levels within 10s of metres. A research reactor 1.6 km south of the site contributed significant (p < 0.01) local fallout 3H but its influence did not reach as far as the disposal trenches.The elevated 3H levels in transpirate were, however, substantially lower than groundwater concentrations measured across the site (ranging from 0 to 91% with a median of 2%). Temporal patterns of tree transpirate 3H, together with local meteorological observations, indicate that soil water within the active root zones comprised a mixture of seepage and rainfall infiltration. The degree of mixing was variable given that the soil water activity concentrations were heterogeneous at a scale equivalent to the effective rooting volume of the trees. In addition, water taken up by roots was not well mixed within the trees. Based on correlation modelling, net rainfall less evaporation (a surrogate for infiltration) over a period of from 2 to 3 weeks prior to sampling seems to be the optimum predictor of transpirate 3H variability for any sampled tree at this site.The results demonstrate successful use of 3H in transpirate from trees to indicate the presence and general extent of sub-surface contamination at a low-level nuclear waste site.  相似文献   

15.
Measurements of Lake Huron water as supplied to the Midland location of the Dow Chemical Company over the period 1970–1981 show that a mean concentration of ≈ 3 pCi/L gross beta activity held relatively constant with a range of yearly mean values from 2 to 4 pCi/L and a range of individual values from 1 to 7 pCi/L. This is comparable to observed values for other Great Lakes' waterways reported in the litarature. There was no apparent seasonal fluctuation. Midland area river water for 1967–1981 show median values of 3 to 4 pCi/L and a range of 2 to 11 pCi/L, comparable to those reported in the literature from througout the United States. The observed activity concentrations in the water are well below the limits of the EPA drinking water standards.  相似文献   

16.
Alpha-autoradiographic and radiochemical studies of the distributions of transuranic nuclides in the tissues and organs of mussels collected from the vicinity of the British Nuclear Fuels plc reprocessing plant at Sellafield, Cumbria, England, appeared to require assessment also of baseline alpha-activities of natural 210 Po levels. Results for the latter were found to be in excess of the anthropogenic activities of Pu and Am isotopes. To ensure that the levels of 210 Po in Cumbrian mussels were not artificially enhanced by local discharges and in the absence of published data, mussels from remote British and French coastal sites were also analyzed. General similarities in 210Po concentrations (111 to 459 Bq kg−1 dry) found in mussels soft parts suggest that the 210Po levels in the Ravenglass mussels (279 Bq kg−1) are natural and largely unsupported by 210Pb; however these levels are as much as four times greater than the present day 239+240Pu concentrations in the same samples. As the transuranic nuclide content of Cumbrian mussels produces a major component of the local critical group radiation exposure from the Sellafield discharges, this finding places in some perspective the significance of the baseline natural radionuclide concentrations in generating total exposure of the public. More specifically, these findings severely limit the usefulness of alpha-autoradiographic studies for transuranic nuclides performed on such samples. Because of the recently lower concentrations of alpha-emitting transuranic nuclides (mainly 238Pu, 239+240Pu and 241Am) in the Ravenglass environment, natural 210Po is now a major contributor to alpha-track distributions in autoradiographic studies.  相似文献   

17.
Measurements of the disequilibria of 234Th/238U in seawater and in suspended particulate and seabed sediment in the eastern Irish Sea reveal that the residence time of dissolved 234Th (0·5–7·7 days) is controlled by the concentration of particles in suspension (0·4–6·9 mg litre−1, which reflects the rate of sediment resuspension (0·5–5·9 kg m−2y−1). The residence time of 234Th with respect to removal to the seabed is longer (7–50 d) and is less dependent on variations in the suspended load. Anthropogenic sources of 238U contribute up to 8–15% of the water column production of 234Th. Enhanced scavenging occurs near the coast and there appears to be a net horizontal flux of 234Th within this region.  相似文献   

18.
A holistic appraisal of the quality of groundwater from the Tuticorin District has been conducted using multivariate statistical and spatial analyses. The objectives of the study were to delineate the spatial and temporal variabilities in groundwater quality and to understand its suitability for human uses. A total of 100 groundwater samples were collected and analyzed for major cations and anions during pre-monsoon and post-monsoon. Water quality index rating was calculated to quantify overall water quality for human consumption. The PRM samples exhibit poor quality in greater percentage when compared with POM due to the dilution after rainfall. Correlation, factor analysis, and plot of the factor scores reflect the seawater intrusion and weathering process. The mineral stability diagrams indicated that the groundwater is in equilibrium with kaolinite and Ca-montmorillonite, whereas Gibbs plot showed that the chemical composition of groundwater in both districts is controlled by the natural weathering processes irrespective of seasons. The major water type identified in this study is the Ca2+–Mg2+–HCO3 ? type, which degrades into predominantly Na+–Cl?–SO4 2? more saline groundwater toward the coast.  相似文献   

19.
226Ra has been measured in five asbestos group minerals. The activity levels are variable, are consistent with other forms of rock and range from 0.01–0.4 pCi 226Ra/g. Alpha particles from asbestos fibers immobilized in the lower lung near pleural surfaces and in the upper lung on bronchial surfaces may be implicated in initiating mesothelioma and bronchial carcinoma.  相似文献   

20.
In the past decades limited amounts of tritium were handled on the CEA site of Bruyères le Châtel with authorised atmospheric releases. A small fraction of the tritium released entered into environmental samples under three forms: (i) as part of free water (TFWT - Tissue Free Water Tritium), or associated with organic matter in two ways; either (ii) bound to the oxygen and nitrogen atoms of the material as exchangeable organically bound tritium (E-OBT), or (iii) bound to carbon atoms as non exchangeable organically bound tritium (NE-OBT). The first two components provide only a picture of atmospheric tritium concentrations at the sampling time as they are in equilibrium with atmospheric moisture and soil humidity. Unlike these exchangeable forms, however, NE-OBT is tightly bound to the organic matter and provides an integrated record of atmospheric tritium during the growing phase of the vegetation. We mapped NE-OBT in tree leaf samples in an area of about 25 × 30 km2 around the centre of the CEA site and compared the results with those obtained during a previous sampling exercise in 1989. At this time, the activity levels were almost ten times higher than those observed presently in a similar area almost 20 years later which is consistent with the decrease of atmospheric releases issued from the centre. As the activity levels are now close to environmental background specific attention was also paid to the analytical procedure to ensure reliable low level NE-OBT detection.  相似文献   

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