Consequences for Norway from a hypothetical accident at the Sellafield reprocessing plant: Atmospheric transport of radionuclides.

The potential consequences for Norway should a nuclear accident at the Sellafield nuclear site occur, have been of concern for Norwegian authorities for several decades. Meteorological data from a 33-year period and the dispersion model 'SNAP' were used to evaluate meteorological conditions for which atmospheric transport of radionuclides from Sellafield to Norway would lead to the most severe impacts. The worst-case meteorological scenario for Norway, was found on 25th June 1989 for a low elevation (0-800 m) release and on 29th June 2001 for a higher elevation (800-1600 m) release. In both cases the western part of Norway was most affected. In general, the probability for depositions (>10 Bq/m2 of 137Cs) increased about 40% during the autumn and winter compared to the spring and summer months. An influence of climate change on the depositions was analysed, but not verified. Results from a number of simulations were also compared to identify how factors such as radioactive particle characteristics and initial release conditions could affect the predicted radionuclide deposition. The impact on predicted total depositions as well as hot-spot depositions by varying particle density and size as well as release elevation in worst-case scenario simulations amounted to about 40%-50%.

Uncertainties in short term prediction of atmospheric dispersion of radionuclides. A case study of a hypothetical accident in a nuclear floating power plant off the West coast of Norway.

Short-term predictions for dispersion of radionuclides in the atmosphere following releases from nuclear incidents are associated with uncertainties originating from meteorology, source term and parameterization. Characterization of these uncertainties is of key importance for preparedness, decision making during an accident and for the further uncertainty propagation in the subsequent modelling of human and ecosystem exposures. Increased traffic of nuclear-propulsion vessels in Norwegian territorial waters gives rise to growing concern of a potential nuclear accident along the coast of Norway. In the present study, we have quantified and inter-compared the uncertainties associated with the model outputs for a hypothetical loss of coolant accident with an ensuing fire in a nuclear vessel situated along the Norwegian coastline, applying two different atmospheric dispersion models: the SNAP Lagrangian particle model (SNAP-Severe Nuclear Accident Program) and the DIPCOT Lagrangian puff model (DIPCOT - Dispersion over Complex Terrain). The case highlights a situation with atmospheric transport from the offshore area to the coast of Western Norway, combined with large wet deposition in inland mountainous terrain, i.e. a common weather situation in this region. The meteorological data include an Ensemble Prediction System with nine ensemble members in addition to a deterministic base run. Five different 7 h emission scenarios with the same total released activity were considered. Hourly wind data at 10 m above ground for a 24 h period, showed that 36% of the wind direction and 41% of the wind speed data were outside the spread of the meteorological ensemble. About 55% and 13% of the measured values fell outside the ensemble for hourly 2 m above ground temperatures and 3 hourly accumulated precipitation, respectively, indicating that the ensemble did not cover all uncertainties in the meteorological fields. The maps of accumulated concentrations and depositions were qualitatively similar for the two models, but SNAP predicted higher accumulated concentration levels compared to DIPCOT for quite large areas, while DIPCOT yielded larger total depositions in the same areas. Furthermore, the direction, speed of movement and spatial extension of the radioactive plume from the accident varied considerably from one model to the other. The spread in the dispersion of the radionuclides ranged from a factor of about 1-3 in the source area to a factor of about 2-5 further away. The spreads due to meteorology and emission scenarios were of similar magnitude. Considering the ratio of the 50th percentiles of the two models, the spread varied by a factor of about 1-9, indicating that uncertainties arising from the formulation of the dispersion model could be as important or even larger than those associated with meteorology and emissions. Thus, it is recommended to include the uncertainty originating from the choice of the dispersion model into the overall uncertainty of short-term prediction of the dispersion of radionuclides and to exploit this further by generating an ensemble of several dispersion models.

Validation of a fuel particle dissolution model with samples from the Red Forest within the Chernobyl exclusion zone.

The contamination in the near exclusion zone of the Chernobyl nuclear power plant (ChNPP) with 90Sr, 238-240Pu and 241Am is associated with irradiated nuclear fuel particles. Fit for purpose models enabling long term prediction of mobility and bioavailability of particle-associated radionuclides are crucial for radiation protection of humans and the environment, as well as for planning of remediation measures and future land use. In the present work, a dynamic fuel particle dissolution model developed in 1999-2002 is described and validated using data based on sampling in 2015. The model is based on the characterization of the radionuclide source term of the waste in a shallow sub-surface radioactive waste storage, trench #22, in the Chernobyl Pilot Site (CPS) located in the Red Forest, 2.5 km west of the ChNPP, as well as the description of physical and chemical properties of the fuel particles and subsequent radionuclide leaching into the soil solution. Transformation rate constants of the fuel particle dissolution model related to topsoil, radioactive waste trench and submerged materials, and drained cooling pond sediments, should largely control the mobility and bioavailability of radionuclides (e.g., solubility in the soil, migration to groundwater and transfer to plants). The predicting power of the Chernobyl fuel particle dissolution model with respect to radionuclide leaching dynamics was validated using samples from the same experimental site, showing that predicted particle leaching and subsequent mobility and bioavailability were within 46 ± 3% of the observed data. Therefore, linking source- and release-scenario dependent characteristics of radioactive particles to their potential weathering can provide information that can be implemented in impact assessments models for existing contaminated areas as well as for future events.

Radioactive particles released from different sources in the Semipalatinsk Test Site.

A total of 456 nuclear tests were performed from 1949 to 1989 at the Semipalatinsk Test Site (STS) in Kazakhstan, as part of the nuclear weapon test program of the USSR. To identify if radionuclides such as 137Cs, 90Sr, 241Am, 239+240Pu were associated with radioactive particles, soil samples were collected at selected contaminated sites (i.e. Experimental field, Excavation sites, Fallout plume sections, Background global fallout area, and Degelen Mountain) within the STS. A series of techniques have been applied to identify the size distributions of radionuclides, the prevalence of radioactive particles in soils, and the degree of leachability of particle associated radionuclides by different agents. In addition, selected particles were characterized non-destructively using digital autoradiography, environmental scanning electron microscopy (ESEM) and synchrotron radiation microscopic X-ray techniques. Radioactive particles were identified at all sites; large vitrified particles were identified at epicenters, and the size of particles decreased along the plume with distance from the epicenters. The radioactive particles identified varied in composition, size and leachability. In general, 137Cs, 241Am, 239+240Pu were strongly associated with solid phases (90-99%) in soils, while 90Sr exhibited much greater variability. The fraction of 90Sr present in exchangeable forms was low close to epicenters, while the extractability increased along the plume as the particle size distribution decreased. The results suggest that at least four different types of radioactive particles are present at STS: 1) Relatively large spherical particles with a shiny glazed, melted surface with internal porous structure, and surface layers enriched in transuranic elements, identified at epicenters of detonations, 2) Vitrified irregular particles probably originating from debris of nuclear device with interactions from soil components, also identified at epicenters of detonations, 3) Particles with visually unchanged structure, containing micro-inclusions of fissile materials associated with soil components, also identified at epicenters; 4) Particles with amorphous structures associated with underground detonations, identified in soil in the vicinity of the entrance of the detonation tunnels at the Degelen Mountain. These were probably formed by secondary mechanisms due to sorption and fixation of radionuclides. Thus, the present work shows that the STS should be considered an important observatory site to link particle characteristics to specific sources and to release conditions as well as to ecosystem transfer of particle associated radionuclides.

Using a chain of models to predict health and environmental impacts in Norway from a hypothetical nuclear accident at the Sellafield site.

When a nuclear accident occurs, decision makers in the affected country/countries would need to act promptly to protect people, the environment and societal interests from harmful impacts of radioactive fallout. The decisions are usually based on a combination of model prognoses, measurements, and expert judgements within in an emergency decision support system (DSS). Large scale nuclear accidents would need predictive models for the atmospheric, terrestrial, freshwater, and marine ecosystems, for the connections between these in terms of radionuclide fluxes, and for the various exposure pathways to both humans and biota. Our study showed that eight different models and DSS modules could be linked to assess the total human and environmental consequences in Norway from a hypothetical nuclear accident, here chosen to be the Sellafield nuclear reprocessing plant. Activity concentrations and dose rates from 137Cs for both humans and the environment via various exposure routes were successfully modelled. The study showed that a release of 1% of the total inventory of 137Cs in the Highly Active Liquor Tanks at Sellafield Ltd is predicted to severely impact humans and the environment in Norway if strong winds are blowing towards the country at the time of an accidental atmospheric release. Furthermore, since the models did not have built-in uncertainty ranges when this Sellafield study was performed, investigations were conducted to identify the key factors contributing to uncertainty in various models and prioritise the ones to focus on in future research.

Why is the multiple stressor concept of relevance to radioecology?

Purpose: A number of nuclear and radiological sources have contributed or are still contributing to the release of a series of stressors such as radionuclides in combination with trace metals and even organic chemicals. To assess the impact of mixed contamination, a limited number of stressors are usually evaluated one by one. We have therefore evaluated the benefit of using the multiple stressor concept focusing on key topics within radioecology such as the source term and deposition, ecosystem interactions and exposure, biological uptake and effects including adverse outcome pathways (AOPs), as a basis for assessing impact and risk. Materials and methods: We have extracted information from highly relevant scientific articles (e.g. Web of Science) describing multiple stressor exposure experiments where at least one stressor is ionizing radioactivity such as low dose gamma radiation or radionuclides (e.g. fission or activation products; uranium and daughter nuclides). In addition, experiences obtained during recent years at the author´s laboratories are included in the discussions, especially when it comes to speciation issues, combined effects, risk estimates, and AOPs. Results: The multiple stressor concept is not only related to the total concentration of a series of radionuclides and other stressors released from one source or from different sources, but also related to the presence of different physico-chemical forms of individual radionuclides. Due to interactions, the ecosystem transfer to biota is dynamic, and the application of toxicokinetics and toxicodynamics considerations seems most useful. Although there is a limited number of articles dealing with multiple stressors in which ionizing radiation is included as one of the stressors, deviation from concentration (dose) additive responses should probably be expected, especially under field conditions where additional abiotic as well as biotic interactions take place Conclusions: Following severe nuclear events, releases can be described as a massive multiple stressor exposure containing radionuclides combined with other stressors. Thus, advanced characterization technologies are needed for parameterization of the mixed stressor source term as input to ecosystem transport, dose, and impact models. To reduce uncertainties in assessments of these complex exposures, advanced technologies and computational efforts to link internal distributions to responses are also needed to understand how multiple stressor exposure could affect toxicokinetics and toxicodynamics, and why combined exposures could depart from additivity along the source-adverse outcome continuum.

A framework for exposure characterization and gamma dosimetry at the NMBU FIGARO irradiation facility.

PURPOSE: The FIGARO low dose 60Co gamma irradiation facility at the Norwegian University of Life Sciences, Ås, Norway, is dedicated to the study of effects on living organisms from acute or chronic ionizing radiation exposures, either alone or in combination with other stressors such as UV radiation, metals or radionuclides. Here, we present a framework of working guidelines and computer software for characterization of absorbed dose rates and accumulated doses to organisms exposed within the continuous gamma field at FIGARO. The aims of the framework are to ensure gamma exposures are well characterized, that results from exposures are correctly interpreted in terms of absorbed dose rates and accumulated doses, and that sufficient information is available so that exposures can be reproduced later or at other facilities. METHODS: The software of the framework includes a Geant4 application for Monte Carlo radiation transport simulations and tools for dose planning, recording and reporting. The working guidelines are prepared for expert users who provide simulated, calculated or estimated absorbed dose rates and for regular users who conduct exposure experiments and are responsible for record keeping. To demonstrate the developed framework, we use a case study where 14 freshwater microcosms are exposed to four levels of gamma dose rates at FIGARO. CONCLUSION: The framework guides users towards good dosimetry practices. Lessons learned could be transferable to other gamma irradiation facilities.

No Fukushima Dai-ichi derived plutonium signal in marine sediments collected 1.5-57km from the reactors.

Based on AMS analysis, it is shown that no Pu signals from the Fukushima accident could be discerned in marine sediments collected 1.5-57km away from the Fukushima Da-ichi power plant (FDNPP), which were clearly influenced by accident-derived radiocesium. The 240Pu/239Pu atom ratios (0.21-0.28) were significantly higher than terrestrial global fallout (0.182 ± 0.005), but still in agreement with pre-FDNPP accident baseline data for Pu in near coastal seawaters influenced by global fallout and long-range transport of Pu from the Pacific Proving Grounds.

Visual modelling suggests a weak relationship between the evolution of ultraviolet vision and plumage coloration in birds.

Birds have sophisticated colour vision mediated by four cone types that cover a wide visual spectrum including ultraviolet (UV) wavelengths. Many birds have modest UV sensitivity provided by violet-sensitive (VS) cones with sensitivity maxima between 400 and 425 nm. However, some birds have evolved higher UV sensitivity and a larger visual spectrum given by UV-sensitive (UVS) cones maximally sensitive at 360-370 nm. The reasons for VS-UVS transitions and their relationship to visual ecology remain unclear. It has been hypothesized that the evolution of UVS-cone vision is linked to plumage colours so that visual sensitivity and feather coloration are 'matched'. This leads to the specific prediction that UVS-cone vision enhances the discrimination of plumage colours of UVS birds while such an advantage is absent or less pronounced for VS-bird coloration. We test this hypothesis using knowledge of the complex distribution of UVS cones among birds combined with mathematical modelling of colour discrimination during different viewing conditions. We find no support for the hypothesis, which, combined with previous studies, suggests only a weak relationship between UVS-cone vision and plumage colour evolution. Instead, we suggest that UVS-cone vision generally favours colour discrimination, which creates a nonspecific selection pressure for the evolution of UVS cones.

Retention of radioactive particles and associated effects in the filter-feeding marine mollusc Mytilus edulis.

Radioactive particles are aggregates of radioactive atoms that may contain significant activity concentrations. They have been released into the environment from nuclear weapons tests, and from accidents and effluents associated with the nuclear fuel cycle. Aquatic filter-feeders can capture and potentially retain radioactive particles, which could then provide concentrated doses to nearby tissues. This study experimentally investigated the retention and effects of radioactive particles in the blue mussel, Mytilus edulis. Spent fuel particles originating from the Dounreay nuclear establishment, and collected in the field, comprised a U and Al alloy containing fission products such as (137)Cs and (90)Sr/(90)Y. Particles were introduced into mussels in suspension with plankton-food or through implantation in the extrapallial cavity. Of the particles introduced with food, 37% were retained for 70 h, and were found on the siphon or gills, with the notable exception of one particle that was ingested and found in the stomach. Particles not retained seemed to have been actively rejected and expelled by the mussels. The largest and most radioactive particle (estimated dose rate 3.18 ± 0.06 Gyh(-1)) induced a significant increase in Comet tail-DNA %. In one case this particle caused a large white mark (suggesting necrosis) in the mantle tissue with a simultaneous increase in micronucleus frequency observed in the haemolymph collected from the muscle, implying that non-targeted effects of radiation were induced by radiation from the retained particle. White marks found in the tissue were attributed to ionising radiation and physical irritation. The results indicate that current methods used for risk assessment, based upon the absorbed dose equivalent limit and estimating the "no-effect dose" are inadequate for radioactive particle exposures. Knowledge is lacking about the ecological implications of radioactive particles released into the environment, for example potential recycling within a population, or trophic transfer in the food chain.

LA-ICP-MS for Pu source identification at Mayak PA, the Urals, Russia.

Information on Pu in environmental samples is traditionally based on the determination of the (240+239)Pu activity via Alpha Spectrometry (AS). A large number of alpha spectrometry sources (planchettes) containing radiochemically separated Pu are therefore stored worldwide and are available for further analyses. These archive samples represent a resource from which valuable information on isotopic composition of alpha emitters including Pu can be obtained. The relative abundances of Pu isotopes can be used to trace specific Pu sources and characterize the relative contributions of different Pu sources in a sample. Thus, in addition to the total (239+240)Pu activity, determination of the (240)Pu/(239)Pu ratio can provide valuable information on the nature of the Pu emitting sources. The Pu isotopic ratios can be determined by mass spectrometry techniques such as Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICPMS) or Accelerator Mass Spectrometry (AMS) that require dissolution and complete destruction of the material deposited on the planchettes. In this study Laser Ablation (LA)-quadrupole-ICP-MS has been employed for the analysis of (239)Pu/(240)Pu ratios from alpha-planchettes prepared from samples originating from the Mayak PA nuclear facility, Russia. The results are compared with data from AMS and show that the (240)Pu/(239)Pu ratios obtained by LA-ICP-MS can be utilized to distinguish weapons-grade Pu from civil reprocessing sources. Moreover, isotope ratio mapping can also be performed across the planchettes, allowing e.g. the visualization of possible inhomogeneities in the Pu-isotope distribution on their surface. Thus, this solid sample technique can be applied to extract additional information from existing archives of samples.

Chronology of Pu isotopes and 236U in an Arctic ice core.

In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 µBq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores.

Micro-analytical characterisation of radioactive heterogeneities in samples from Central Asian TENORM sites.

The present work focuses on the use of micro-analytical techniques to demonstrate the heterogeneous distribution of radionuclides and metals in soils collected at Former Soviet Union mining sites in Central Asia. Based on digital autoradiography, radionuclides were heterogeneously distributed in soil samples collected at the abandoned uranium mining sites Kurday, Kazakhstan, Kadji Sai, Kyrgyzstan and Taboshar, Tajikistan. Using electron microscopy interfaced with X-ray microanalysis submicron - mm-sized radioactive particles and rock fragments with U, As, Se and toxic metals on the surfaces were identified in Kurday and Kadji Sai samples. Employing scanning and tomographic (3D) synchrotron radiation based micro-X-ray fluorescence (µ-SRXRF) and synchrotron radiation based micro-X-ray diffraction (µ-SRXRD) allowed us to observe the inner structure of the particles without physical sectioning. The distribution of elements in virtual crosssections demonstrated that U and a series of toxic elements were rather heterogeneously distributed also within individual radioactive TENORM particles. Compared to archived data, U in Kadji Sai particles was present as uraninite (U4O9+y or UO2+x) or Na-zippeite ((Na4(UO2)6[(OH)10(SO4)3]·4H2O), i.e. U minerals with very low solubility. The results suggested that TENORM particles can carry substantial amount of radioactivity, which can be subject to re-suspension, atmospheric transport and water transport. Thus, the potential radioecological and radioanalytical impact of radioactive particles at NORM and TENORM sites worldwide should be taken into account. The present work also demonstrates that radioecological studies should benefit from the use of advanced methods such as synchrotron radiation based techniques.

Environmental impact assessment of radionuclide and metal contamination at the former U site at Kadji Sai, Kyrgyzstan.

During 1949-1967, a U mine, a coal-fired thermal power plant and a processing plant for the extraction of U from the produced ash were operated at the Kadji Sai U mining site in Tonsk district, Issyk-Kul County, Kyrgyzstan. The Kadji Sai U legacy site represents a source of contamination of the local environment by naturally occurring radionuclides and associated trace elements. To assess the environmental impact of radionuclides and trace metals at the site, field expeditions were performed in 2007 and 2008 by the Joint collaboration between Norway, Kazakhstan, Kyrgyzstan, Tajikistan (JNKKT) project and the NATO SfP RESCA project. In addition to in situ gamma and Rn dose rate measurements, sampling included at site fractionation of water and sampling of water, fish, sediment, soils and vegetation. The concentrations of radionuclides and trace metals in water from Issyk-Kul Lake were in general low, but surprisingly high for As. Uptake of U and As was also observed in fish from the lake with maximum bioconcentration factors for liver of 1.6 and 75, respectively. The concentrations of U in water within the Kadji Sai area varied from 0.01 to 0.05 mg/L, except for downstream from the mining area where U reached a factor of 10 higher, 0.2 mg/L. Uranium concentrations in the drinking water of Kadji Sai village were about the level recommended by the WHO for drinking water. The (234)U/(238)U activity ratio reflected equilibrium conditions in the mining pond, but far from equilibrium outside this area (reaching 2.3 for an artesian well). Uranium, As and Ni were mainly present as low molecular mass (LMM, less than 10 kDa) species in all samples, indicating that these elemental species are mobile and potentially bioavailable. The soils from the mining sites were enriched in U, As and trace metals. Hot spots with elevated radioactivity levels were easily detected in Kadji Sai and radioactive particles were observed. The presence of particles carrying significant amount of radioactivity and toxic trace elements may represent a hazard during strong wind events (wind erosion). Based on sequential extractions, most of the elements were strongly associated with mineral matter, except for U and As having a relatively high remobilization potential. Low Kd was obtained for U (3.5 × 10(2) L/kg d.w.), intermediate Kds (~3 × 10(3) L/kg d.w.) were obtained for (226)Ra, As and Ni, while a high Kd (2.2 × 10(5) L/kg d.w.) were obtained for Pb. The accumulation of metals in fish gills reflected the LMM species in the Issyk-Kul water, and did not show any bioaccumulation. The muscle Hg concentrations in all fish species were low and did not represent any health risk even for groups at risk. Total gamma and Rn dose rate to man amounted to about 12 mSv/y, while the highest calculated dose rate for non-human species based on the ERICA Assessment Tool were obtained in terrestrial plants (164 µGy/h) due to the Ra exposure. The results obtained showed that radiation doses to resident public at all of the investigated sites in the Kadji Sai area were in general relatively low. Low radiological risk and no detrimental health impact on resident public can be expected at these sites. However, exposure to Rn and Tn in the living environment can be further reduced by implementing simple countermeasures such as ventilation of dwelling cellars. More focus in the Kadji Sai area should probably be put on trace elements, especially the As uptake in fish in Lake Issyk-Kul.

Apparent bioaccumulation of cylindrospermopsin and paralytic shellfish toxins by finfish in Lake Catemaco (Veracruz, Mexico).

Compared to the well-characterized health threats associated with contamination of fish and shellfish by algal toxins in marine fisheries, the toxicological relevance of the bioaccumulation of toxins from cyanobacteria (blue-green algae), as the primary toxigenic algae in freshwater systems, remains relatively unknown. Lake Catemaco (Veracruz, Mexico) is a small, tropical lake system specifically characterized by a year-round dominance of the known toxigenic cyanobacterial genus, Cylindrospermopsis, and by low, but detectable, levels of both a cyanobacterial hepatotoxin, cylindrospermopsin (CYN), and paralytic shellfish toxins (PSTs). In the present study, we evaluated, using enzyme-linked immunoassay (ELISA), levels of both toxins in several species of finfish caught and consumed locally in the region to investigate the bioaccumulation of, and possible health threats associated with, these toxins as potential foodborne contaminants. ELISA detected levels of both CYN and PSTs in fish tissues from the lake. Levels were generally low (≤ 1 ng g(-1) tissue); however, calculated bioaccumulation factors (BAFs) indicate that toxin levels exceed the rather low levels in the water column and, consequently, indicated bioaccumulation (BAF >1). A reasonable correlation was observed between measured bioaccumulation of CYN and PSTs, possibly indicating a mutual source of both toxins, and most likely cells of Cylindrospermopsis, the dominant cyanobacteria in the lake, and a known producer of both metabolites. The potential roles of trophic transport in the system, as well as possible implications for human health with regards to bioaccumulation, are discussed.

Solid state speciation and potential bioavailability of depleted uranium particles from Kosovo and Kuwait.

A combination of synchrotron radiation based X-ray microscopic techniques (mu-XRF, mu-XANES, mu-XRD) applied on single depleted uranium (DU) particles and semi-bulk leaching experiments has been employed to link the potential bioavailability of DU particles to site-specific particle characteristics. The oxidation states and crystallographic forms of U in DU particles have been determined for individual particles isolated from selected samples collected at different sites in Kosovo and Kuwait that were contaminated by DU ammunition during the 1999 Balkan conflict and the 1991 Gulf war. Furthermore, small soil or sand samples heavily contaminated with DU particles were subjected to simulated gastrointestinal fluid (0.16 M HCl) extractions. Characteristics of DU particles in Kosovo soils collected in 2000 and in Kuwait soils collected in 2002 varied significantly depending on the release scenario and to some extent on weathering conditions. Oxidized U (+6) was determined in large, fragile and bright yellow DU particles released during fire at a DU ammunition storage facility and crystalline phases such as schoepite (UO(3).2.25H(2)O), dehydrated schoepite (UO(3).0.75H(2)O) and metaschoepite (UO(3).2.0H(2)O) were identified. As expected, these DU particles were rapidly dissolved in 0.16 M HCl (84 +/- 3% extracted after 2 h) indicating a high degree of potential mobility and bioavailability. In contrast, the 2 h extraction of samples contaminated with DU particles originating either from corrosion of unspent DU penetrators or from impacted DU ammunition appeared to be much slower (20-30%) as uranium was less oxidized (+4 to +6). Crystalline phases such as UO(2), UC and metallic U or U-Ti alloy were determined in impacted DU particles from Kosovo and Kuwait, while the UO(2,34) phase, only determined in particles from Kosovo, could reflect a more corrosive environment. Although the results are based on a limited number of DU particles, they indicate that the structure and extractability of DU particles released from similar sources (metallic U penetrators) will depend on the release scenarios (fire, impact) and to some extent environmental conditions. However, most of the DU particles (73-96%) in all investigated samples were dissolved in 0.16 M HCl after one week indicating that a majority of the DU material is bioaccessible.

Characterization of U/Pu particles originating from the nuclear weapon accidents at Palomares, Spain, 1966 and Thule, Greenland, 1968.

Following the USAF B-52 bomber accidents at Palomares, Spain in 1966 and at Thule, Greenland in 1968, radioactive particles containing uranium (U) and plutonium (Pu) were dispersed into the environment. To improve long-term environmental impact assessments for the contaminated ecosystems, particles from the two sites have been isolated and characterized with respect to properties influencing particle weathering rates. Low (239)Pu/(235)U (0.62-0.78) and (240)Pu/(239)Pu (0.055-0.061) atom ratios in individual particles from both sites obtained by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) show that the particles contain highly enriched U and weapon-grade Pu. Furthermore, results from electron microscopy with Energy Dispersive X-ray analysis (EDX) and synchrotron radiation (SR) based micrometer-scale X-ray fluorescence (micro-XRF) 2D mapping demonstrated that U and Pu coexist throughout the 1-50 microm sized particles, while surface heterogeneities were observed in EDX line scans. SR-based micrometer-scale X-ray Absorption Near Edge Structure Spectroscopy (micro-XANES) showed that the particles consisted of an oxide mixture of U (predominately UO(2) with the presence of U(3)O(8)) and Pu ((III)/(IV), (IV)/(V) or (III), (IV) and (V)). Neither metallic U or Pu nor uranyl or Pu(VI) could be observed. Characteristics such as elemental distributions, morphology and oxidation states are remarkably similar for the Palomares and Thule particles, reflecting that they originate from similar source and release scenarios. Thus, these particle characteristics are more dependent on the original material from which the particles are derived (source) and the formation of particles (release scenario) than the environmental conditions to which the particles have been exposed since the late 1960s.

Characterization of uranium and plutonium containing particles originating from the nuclear weapons accident in Thule, Greenland, 1968.

To improve long-term radioecological impact assessment for the contaminated ecosystem of Bylot Sound, Greenland, U and Pu containing particles have been characterized with respect to particle size, elemental distribution, morphology and oxidation states. Based on scanning electron microscopy with XRMA, particles ranging from about 20 to 40 microm were isolated. XRMA and mu-XRF mapping demonstrated that U and Pu were homogeneously distributed throughout the particles, indicating that U and Pu have been fused. Furthermore, mu-XANES showed that U and Pu in the particles were present as mixed oxides. U was found to be in oxidation state IV whereas Pu apparently is a mixture of Pu(III) and Pu(IV). As previous assessments are based on PuO2 only, revisions should be made, taking Pu(III) into account.

Oxidation states of uranium in depleted uranium particles from Kuwait.

The oxidation states of uranium in depleted uranium (DU) particles were determined by synchrotron radiation based mu-XANES, applied to individual particles isolated from selected samples collected at different sites in Kuwait. Based on scanning electron microscopy with X-ray microanalysis prior to mu-XANES, DU particles ranging from submicrons to several hundred micrometers were observed. The median particle size depended on sources and sampling sites; small-sized particles (median 13 microm) were identified in swipes taken from the inside of DU penetrators holes in tanks and in sandy soil collected below DU penetrators, while larger particles (median 44 microm) were associated with fire in a DU ammunition storage facility. Furthermore, the (236)U/(235)U ratios obtained from accelerator mass spectrometry demonstrated that uranium in the DU particles originated from reprocessed fuel (about 10(-2) in DU from the ammunition facility, about 10(-3) for DU in swipes). Compared to well-defined standards, all investigated DU particles were oxidized. Uranium particles collected from swipes were characterized as UO(2), U(3)O(8) or a mixture of these oxidized forms, similar to that observed in DU affected areas in Kosovo. Uranium particles formed during fire in the DU ammunition facility were, however, present as oxidation state +5 and +6, with XANES spectra similar to solid uranyl standards. Environmental or health impact assessments for areas affected by DU munitions should therefore take into account the presence of respiratory UO(2), U(3)O(8) and even UO(3) particles, their corresponding weathering rates and the subsequent mobilisation of U from oxidized DU particles.

Radionuclide speciation and its relevance in environmental impact assessments.

To assess the long-term environmental impact of radioactive contamination of ecosystems, information on source terms including radionuclide speciation, mobility and biological uptake is needed. A major fraction of refractory radionuclides released from nuclear sources such as nuclear weapons tests and reactor accidents is present as radioactive particles, whilst radionuclides are also present as colloids or low molecular mass species in effluents from nuclear installations. Low molecular mass species are more mobile (lower apparent K(d)) and bioavailable (higher apparent BCF) than colloids and particles. Soils and sediments act as sinks for particles and colloids. Due to particle weathering, associated radionuclides can be remobilised over time. Thus, information on particle characteristics such as composition, particle size, crystalline structures and oxidation states influencing weathering rates and subsequent mobilisation is essential. The present article summarises current knowledge on radioactive particles released from different sources, and the relevance of radionuclide speciation for mobility and biological uptake.