Hot particles of the Yenisei River flood plain, Russia.

Some high-activity hot particles (HP) were found in the flood plain of the Yenisei River, near the Krasnoyarsk Mining-and-Chemical Combine (MCC), and their radionuclide compositions were determined. The ratios of plutonium and caesium isotopes in the particles are indicative of their reactor origin. The 137Cs activity of the particles amounts to 29,200 kBq/particle, which is higher than the corresponding activities of the fuel particles that formed as a result of the accident at the Chernobyl NPP. All the particles have been divided into two major groups according to the 137Cs/34Cs ratio: in the first group, the 137Cs/134Cs ratio is more than or equal to 3000, and in the second the 137Cs/134Cs ratio is less than or equal to 1000. The particles of the first and the second groups were preliminarily estimated to be formed 30 and 20 years ago, which suggests that there must have been at least two accidents at the MCC reactors, with part of the fuel released into the Yenisei River.     

Deposition and distribution of Chernobyl fallout fission products and actinides in a Russian soil profile

In this article the distribution of fission products and actinides in a soil profile from Novo Bobovicky in Russia, which was contaminated due to the Chernobyl nuclear power plant accident, is described. The ground deposition of long-lived fission products determined by gamma-spectrometry was (recalculated to 26 April 1986) 1600 kBq (137)Cs/m(2), 900 kBq (134)Cs/m(2) and 60 kBq (125)Sb/m(2). Of these radionuclides (137)Cs shows the dominating activity at the present time. After 6.5 years 90% of the Cs and Sb activity was contained in the upper 4 cm. A (239,240)Pu ground deposition of 77.4+/-8.0 Bq/m(2) was determined by alpha-spectrometry. The (238)Pu/(239,240)Pu activity ratio of 0.30+/-0.03 and (241)Pu/(239,240)Pu activity ratio of 115+/-14 (in 1986) measured in the soil profile, indicates that the analysed Pu originates mainly from the Chernobyl accident. The average (234)U/(238)U activity ratio of 1.06+/-0.29 indicates that the uranium in this soil is dominated by naturally occurring uranium.The alpha- and beta-autoradiography revealed that the activity is mainly present in particulate form. It could further be observed that the spots containing alpha- or beta-activity originated from different particles. A comparison of alpha-autoradiography with the bulk Pu and Am activity showed that 92% of the alpha-activity was present as clearly detectable alpha-spots.The beta-active particles, located by beta-autoradiography were correlated with gamma-spectrometric measurements and contained only (137)Cs. These hot spots ranged from 0.02 to 0.15 Bq.It could be concluded that the vertical transport of (137)Cs and fuel fragments occurs mainly by movement of particles through the soil. It could also be concluded that the fuel fragments found, in this soil were depleted in respect to Cs, Sb and Eu.Comparison of the analysed (238)Pu/(239,240)Pu, (241)Pu/(239,240)Pu and (241)Am/(239,240)Pu ratios with the ratios calculated with ORIGEN-S code gave an estimate of the average burn-up of the fuel particles to be in the range of 11-12 GWd/tU.The results presented in this article are valid for this single soil profile and should not be generalised unless validated in a more rigorous study of a larger number of soil profiles.     

Classification of hot particles from the Chernobyl accident and nuclear weapons detonations by non-destructive methods.

Both after the Chernobyl accident and nuclear weapon detonations, agglomerates of radioactive material, so-called hot particles, were released or formed which show a behaviour in the environment quite different from the activity released in gaseous or aerosol form. The differences in their characteristic properties, in the radionuclide composition and the uranium and actinide contents are described in detail for these particles. While nuclear bomb hot particles (both from fission and fusion bombs) incorporate well detectable trace amounts of 60Co and 152Eu, these radionuclides are absent in Chernobyl hot particles. In contrast, Chernobyl hot particles contain 125Sb and 144Ce which are absent in atomic bomb HPs. Obvious differences are also observable between fusion and fission bombs' hot particles (significant differences in 152Eu/l55Eu, 154Eu/155Eu and 238Pu/239Pu ratios) which facilitate the identification of HPs of unknown provensence. The ratio of 239Pu/240Pu in Chernobyl hot particles could be determined by a non-destructive method at 1:1.5. A non-destructive method to determine the content of non-radioactive elements by Kalpha-emission measurements was developed by which inactive Zr, Nb, Fe and Ni could be verified in the particles.     

Accumulation of radionuclides from radioactive substrata by some micromycetes

Overgrowing (interaction) and dissolution of intact and milled hot particles by various micromycetes were studied under laboratory conditions. Hot particles used for the investigation originated from the Chernobyl accident release and atomic bomb testing sites. The micromycetes investigated were mitosporic fungi mainly isolated from the Chernobyl site and vicinity. Most of the fungal species and strains showed a tendency to grow towards the hot particle, overgrow it and dissolve it after prolonged contact. The accumulation (absorption and adsorption) of radionuclides from intact hot particles was generally more intensive for (152)Eu than for (137)Cs by a factor of about 2.6-134, while in experiments with milled samples the (152)Eu and (137)Cs accumulation was similar, except for some fungal species, which showed higher (152)Eu than (137)Cs sorption. It could be shown that the main factors influencing Cs and Eu accumulation in fungi are: fungal species and strains and the size and composition of the hot particle.     

Artificial radionuclides in the atmosphere over Lithuania

Measurements of airborne radioactive aerosol concentration were carried out on the basis of 1-3 days samples after the Chernobyl disaster and during the period of 1992-2003. Transport of "hot" particles of different composition resulted in the high activity concentrations of (137)Cs, (238)Pu, (239,240)Pu and (241)Am in the atmosphere in Vilnius at the end of April 1986. The (240)Pu/(239)Pu atom ratio showed clear evidence of non-global plutonium originating from the Chernobyl accident in the atmosphere over Lithuania. The (240)Pu/(239)Pu atom ratio ranged from 0.14 to 0.40 in monthly samples in Vilnius in 1995-2003. An increase in activity concentration of (137)Cs by a factor of 100 (up to 300 microBq/m(3)) was found following forest fires in the Ukraine and Belarus. However, no transport of the Chernobyl plutonium was observed and the (240)Pu/(239)Pu atom ratio in samples collected during the forest fires was found to be 0.229 and 0.185, respectively. The exponential decrease in the (240)Pu/(239)Pu atom ratio from 0.30 to 0.19 (mean values) was observed in 1995-2003.     

Radiation measurements and radioecological aspects of fallout from the cherbonyl reactor accident

Fallout from the Chernobyl reactor accident has been monitored for about one year in Thessaloniki in Northern Greece. Fifteen different short-lived, three relatively long- and one long-lived fission products were identified in air, precipitation, soil, grass and milk samples. The iodine-131 and cesium-137 concentrations in air reached 6·5 and 3 Bq m⁻³ respectively, on 6 May, 1986. The external exposure dose rate rose to five times the normal background level. It was estimated that the accumulated dose equivalent to the adult thyroid from inhaled iodine-131 averaged 96 μSv, while the body burden from inhaled radiocesium nuclides averaged 2 μSv, 1000 times lower than that corresponding to the estimated dose equivalent from ingestion of foodstuff, which averaged 2 mSv for the first year after the accident.     

137Cs and 90Sr behavioural regularities in the southeastern part of the Baltic Sea

Variations in 137Cs concentrations were investigated over the period 1986-1997 in the southeastern part of the Baltic Sea, following the Chernobyl power plant accident. The rate of "self-cleaning" was demonstrated to be very slow, the average concentration of 137Cs in 1996 being almost the same as that measured directly after the accident, in 1986. Measurements of both 137Cs and 90Sr concentrations generally revealed homogeneous distributions in this region of the Baltic Sea, though patchy distributions did develop under some hydrometeorological conditions. Specifically, the 137Cs concentration distribution became heterogeneous with values varying in the range 60-92 Bq/m3 under south-southwesterly wind conditions whilst the 90Sr concentration distribution developed similar characteristics with values ranging from 15 to 64 Bq/m3 under east-southeasterly wind conditions. In addition, in coastal waters, over extensive periods of north-northwesterly winds in 1995, 137Cs concentrations increased to values 1.5-2 times the overall average concentration, which was registered in 1986 and 1996. These data therefore reveal a continuing significant pollution of the waters of the Baltic Sea resulting from the Chernobyl power plant accident, a pollution compounded by the slow rate of radionuclide self-cleaning and significant probability of sudden regional concentration increase.     

A pilot study to assess ground-level ambient air concentrations of fine particles and carbon monoxide in urban Guatemala

Ambient concentrations and the elemental composition of particles less than 2.5 microm in diameter (PM2.5), as well as carbon monoxide (CO) concentrations, were measured at ground-level in three Guatemalan cities in summer 1997: Guatemala City, Quetzaltenango, and Antigua. This pilot study also included quantitative and qualitative characterizations of microenvironment conditions, e.g., local meteorology, reported elsewhere. The nondestructive X-ray fluorescence elemental analysis (XRF) of Teflon filters was conducted. The highest integrated average PM2.5. concentrations in an area (zona) of Guatemala City and Quetzaltenango were 150 microg m(-3) (zona 12) and 120 microg m(-3) (zona 2), respectively. The reported integrated average PM2.5 concentration for Antigua was 5 microg m(-3). The highest observed half-hour and monitoring period average CO concentrations in Guatemala City were 10.9 ppm (zona 8) and 7.2 ppm (zonas 8 and 10), respectively. The average monitoring period CO concentration in Antigua was 2.6 ppm. Lead and bromine concentrations were negligible, indicative of the transition to unleaded fuel use in cars and motorcycles. The XRF results suggested sources of air pollution in Guatemala, where relative rankings varied by city and by zonas within each city, were fossil fuel combustion emitting hydrocarbons, combustion of sulfurous conventional fuels, soil/roadway dust, farm/agricultural dust, and vehicles (evaportion of gas, parts' wear).     

Fuel particles in the Chernobyl cooling pond: current state and prediction for remediation options

During the coming years, a management and remediation strategy for the Chernobyl cooling pond (CP) will be implemented. Remediation options include a controlled reduction in surface water level of the cooling pond and stabilisation of exposed sediments. In terrestrial soils, fuel particles deposited during the Chernobyl accident have now almost completely disintegrated. However, in the CP sediments the majority of ⁹⁰Sr activity is still in the form of fuel particles. Due to the low dissolved oxygen concentration and high pH, dissolution of fuel particles in the CP sediments is significantly slower than in soils. After the planned cessation of water pumping from the Pripyat River to the Pond, significant areas of sediments will be drained and exposed to the air. This will significantly enhance the dissolution rate and, correspondingly, the mobility and bioavailability of radionuclides will increase with time. The rate of acidification of exposed bottom sediments was predicted on the basis of acidification of similar soils after liming. Using empirical equations relating the fuel particle dissolution rate to soil and sediment pH allowed prediction of fuel particle dissolution and ⁹⁰Sr mobilisation for different remediation scenarios. It is shown that in exposed sediments, fuel particles will be almost completely dissolved in 15–25 years, while in parts of the cooling pond which remain flooded, fuel particle dissolution will take about a century.     

Reconstruction of radioactive plume characteristics along Chernobyl's Western Trace

Using data obtained from 435 radiation sampling stations in the Red Forest, 1.5 km W if the Chernobyl Nuclear Complex, we reconstructed the deposition pathway of the first plume released by the accident, Chernobyl's Western Trace. The dimensions and deposition rates of the plume remain sharply defined 15 years after the accident. Assuming a uniform particle distribution within the original cloud, we derived estimates of plume dimensions by applying geometric transformations to the coordinates at each sample point. Our derived estimates for the radioactive cloud accounted for 87% of the variation of radioactivity in this region. Results show a highly integrated bell-shaped cross-section of the cloud of radiation, approximately 660 m wide and 290 m high, traveling at a bearing of 264 degrees from reactor IV. Particle sizes within Chernobyl's Western Trace were within the most dangerous range for inhaled aerosols (2-5 microm). Therefore, reconstruction of the dispersion of such particles is critical for understanding the aftermath of nuclear and biological aerosol releases.     

Particle size distribution and its elemental composition in the ambient air of Delhi

This study examines the chemical composition of PM10, the thoracic fraction of the atmospheric particulate matter. An eight-stage Anderson impactor is used to separate the PM10 from other fractions with different aerodynamic behaviour at three different area representative sites in Delhi from February to May 1998. PM10 particulate are subdivided into two fractions, coarse (> 2.1-10 microns) and fine (< 2.1 microns). The concentrations of major heavy metals such as Pb, Zn, Cd, Ni, and Fe are determined by atomic absorption spectrophotometer. The average concentration of coarse fraction of PM10 is found to be 68.3 +/- 17 micrograms/m3 while the fine fraction of PM10 is 71.3 +/- 15 micrograms/m3 for Delhi. Metal concentration (except Fe) in fine fraction exceeds by a factor of up to 6, as compared to that in the coarse fraction. In order to identify the major sources of fine and coarse fraction of PM10, principle component analysis (PCA) was undertaken and three major sources were identified, namely vehicular emissions, industrial emission, and soil resuspension.     

Particle-size distribution of fission products in airborne dust collected at Tsukuba from April to June 1986

The radioactivity released by the reactor accident at Chernobyl was detected in surface air at Tsukuba, Japan. Gamma-spectrometry of airborne dust collected using aerodynamic separation showed higher concentrations of radionuclides in fine particles. The particle-size distribution of radionuclides changed with time.     

The influence of hot particle contamination on Sr and Cs transfers to milk and on time-integrated ingestion doses

Most models for transfers of radionuclides through the food chain typically assume that the radioactivity is initially deposited in chemically available forms. It is known, however, that releases of radionuclides in the form of hot particles may significantly influence their environmental transfers and uptake to the food chain. This study presents models for time changes in ⁹⁰Sr and ¹³⁷Cs in milk which incorporate hot particle contamination using observed rates of hot particle dissolution following the Chernobyl accident. A general equation is presented for the influence of hot particles on overall ingestion doses. As expected from previous work, fallout of hot particles significantly influences time changes in radionuclide activity concentrations in foodstuffs. It is also shown that incorporation of radionuclides in hot particles influences time-integrated ingestion doses. For a situation in which a large proportion (90–100%) of fallout is in slowly dissolving hot particles, time-integrated ingestion doses from ⁹⁰Sr and ¹³⁷Cs are reduced by a factor of approximately two compared to the case where all radioactivity is deposited in bioavailable forms. However, the influence of rapidly dissolving hot particles on time-integrated ingestion doses is relatively minor. Remaining significant uncertainties in dose estimates are discussed.     

A 10-year study of the 137Cs distribution in soil and a comparison of Cs soil inventory with precipitation-determined deposition

During a 10-year period, 1988-1998, surface soil samples have been collected at Blentarp in southern Sweden and analysed for 137Cs from the Chernobyl accident and from the nuclear weapons tests. The distance between the sampling plots on the different sampling occasions has been no more than 3 m. The results show that the depth distribution of 137Cs is very similar for each of the sampling occasions, indicating that the caesium migration at this site is very small. The total activity measured in the soil cores is in agreement with the calculated activity of 137Cs deposited at the site after nuclear weapons tests and the Chernobyl accident, based on air activity concentration and the amount of precipitation. The calculated deposition of 137Cs originating from the bomb tests amounts to 1.41 kBq m-2 for the period 1962-1986, which is in agreement with the activity of nuclear weapons fallout measured in the soil samples (1.60 kBq m-2 as a mean value of the first four years of sampling). The calculated activity of 137Cs of Chernobyl origin was 0.79 kBq m-2, which agrees well with the value of 0.79 kBq m-2 measured in the soil samples in 1988.     

90Sr migration to the geo-sphere from a waste burial in the Chernobyl exclusion zone

Results are presented from an ongoing field-scale experimental study (namely the Chernobyl Pilot Site project) aimed at characterization of processes controlling (90)Sr releases from a shallow trench containing nuclear fuel particles, and subsequent radionuclide transport in the underlying sandy aquifer at the Chernobyl nuclear power plant site. Microscopic analyses of waste material and leaching experiments have shown that 10-30% of the radioactive inventory is associated with chemically extra-stable Zr-U-O particles. The largest fraction of (90)Sr activity in the trench ( approximately 30-60%) is currently associated with relatively slowly dissolving non-oxidized UO(2) matrix fuel particles. The (90)Sr migration velocity in the eolian sand aquifer is retarded by sorption to approximately 9% of groundwater flow velocity (K(d) approximately 2 ml/g). The dispersivity values for non-reactive solute transport in the aquifer predicted by geostatistics (i.e. 0.8 6 cm) were confirmed by a natural gradient tracer test using (36)Cl. The observed negative correlation between hydraulic conductivity and K(d) of aquifer sediments suggests that (90)Sr could be subjected to larger dispersion in the subsurface compared with (36)Cl.     

Soil contamination with 90Sr in the near zone of the Chernobyl accident

Representative large-scale soil sampling on a regular grid of step width about 1 km was carried out for the first time in the near zone of the Chernobyl accident (radius 36 km). An integrated map of terrestrial 90Sr contamination density in the 30 km exclusion zone (scale 1:200,000) has been created from the analysed samples. Maps of the main agrochemical characteristics of the soils, which determine the fuel particle dissolution rates and the contamination of vegetation, were produced. The total contents of 90Sr on the ground surface of the 30 km zone in Ukraine (without the reactor site and the radioactive waste storages) was about 810 TBq (8.1 x 10(+14) Bq) in 1997, which corresponds to 0.4-0.5% of the Chernobyl reactor inventory at the time of the accident. This assessment is 3-4 times lower than previous estimates.     

Precipitation scavenging of 7Be and 137Cs radionuclides in air

Atmospheric depositional fluxes of the naturally occurring 7Be of cosmogenic origin and 137Cs from fallout of the Chernobyl accident were measured over a 6-year period (January 1987-December 1992) at Thessaloniki, Greece (40 degrees 38'N, 22 degrees 58'E). Total precipitation accumulation during 1987-1992 varied between 33.7 cm and 65.2 cm, reflecting a relatively dry (precipitation-free) climate. The activity concentrations of 7Be and 137Cs in rainwater depended on the precipitation rate, being higher for low precipitation rates and lesser for high precipitation rates. 137Cs was removed by rain and snow more efficiently than 7Be. Snowfall was more efficient than rainfall in removing the radionuclides from the atmosphere. The annual bulk depositional fluxes of 7Be varied between 477 and 1133 Bq m(-2) y(-1) and this variability was attributed to the amount of precipitation and the variations of the atmospheric concentrations of 7Be. The annual bulk depositional fluxes of 137Cs showed a significant decrease over time from 1987 to 1992, resulting in a removal half-life of 1.33 years. The presence of 137Cs in air, and therefore in rainwater and snow, long after the Chernobyl accident (26 April 1986) was mainly due to the resuspension process. The normalized depositional fluxes of both radionuclides showed maximal values during the spring season where the maximum amount of precipitation occurred. The relatively high positive correlation between 7Be and 137Cs normalized depositional fluxes indicates that the scavenging process of local precipitation controlled the fluxes of both radionuclides. The dry depositional flux of 7Be was less than 9.37% of total (wet and dry) depositional flux. The fraction of dry-to-total depositional flux of 137Cs was much higher than that of 7Be, due to the resuspended soil.     

Migration ability of radionuclides in soil-vegetation cover of Belarus after Chernobyl accident

This article illustrates the experimental experience achieved in the research of the self-restoration of radioactive-contaminated natural ecosystems. The main directions of studies were: the content and geochemical stability of "hot" particles in radioactive fallout from Chernobyl accident; the physicochemical forms (water-soluble, exchangeable, mobile and fixed) of Cs-137, Sr-90, Pu-239, 240 and Am-241 in the wide varieties of soils; the biological accessibility of radionuclides and their contents in soil pore solutions; and the dynamics and migration parameters of radionuclides vertical redistribution in different landscape conditions.     

Physical characterization of diesel exhaust particles in exposure chambers

Since the deposition of particulate in the respiratory system is strongly influenced by particle size, a correct assessment of this parameter is important for any inhalation experiment studying the potential health effects of air pollutants. Measuring the distribution of particles according to their aerodynamic diameter and mechanical mobility diameter is crucial in analyzing the deposition of submicron particles in the lower respiratory system. Cascade impactor measurements of diluted diesel exhaust in 12.6 m³ animal exposure chambers in the GMR Biomedical Science Department showed that the mass median aerodynamic diameter of the aerosol was 0.2 μm with 88% of the mass in particles smaller than 1 μm. Diffusion battery measurements showed that the mass median mechanical mobility diameter was about 0.11 μm. Transmission electron micrographs of particles deposited on chamber surfaces revealed both agglomerates and nearly spherical particles. The particles in these chambers are similar in size and shape to diesel particles described elsewhere. The flux of diesel particles to food surfaces was measured. Calculations of the expected daily dose by inhalation and by feeding showed that the “worst case” dose by feeding was only about one-tenth the dose by breathing.     

Air radionuclide patterns observed at Monaco from the Chernobyl accident

Radionuclide concentrations in air filters taken in Monaco for several weeks after the Chernobyl accident on April 26, 1986 have been carefully examined. Unusual radionuclides such as ¹⁰⁵Ru, ¹¹¹Ag, ¹²⁵Sn and ¹²⁶Sb were identified as being present in small amounts. Nuclides of the more volatile elements I, Te, and Ag peaked 6–24 hours earlier than the average, whereas the refractory elements exhibited a different distribution. Radionuclide concentrations seen in air at Chernobyl compared with those observed at Monaco show that ^134,137Cs was least removed by environmental processes between the two sites and rare earths the most. The second (4–5 May) peak of activity released from the Chernobyl reactor was characterised by a relatively higher content of refractory elements, also observed at Monaco. The different phases of such an accident can thus be observed even at distances approaching 2000 km.