Oxidation and Release of Ruthenium from White Inclusions

In this paper the laboratory test results on oxidation and release of ruthenium as a fission product element are summarised. The ruthenium appears in the nuclear fuel pellets of pressurized water reactors as one of the fission product elements during burnup. In case of severe accident when the air can contact the degraded hot fuel, the ruthenium oxidises and its gaseous oxides, especially the RuO4, release rapidly from the pellets to the environment. Because of high radio- and chemotoxicity of ruthenium tetra-oxide further experimental study of oxidation and release is essential. It is well known that ruthenium in the irradiated fuel UO2 fuel appears in small metallic alloy precipitations together with fission product elements as Mo, Rh, Pd and Tc. The precipitations are seen in the metallographic pictures as white inclusions. This separate effect study focused on the differences in the release rate of gaseous ruthenium oxides when pure ruthenium or Mo-Ru-Rh-Pd metallic alloy is present in the simulated nuclear fuel. The oxidation and release were studied at constant reaction temperatures of 1000 or 1100 Celsius. The tests showed that during high-temperature oxidation of the Mo-Ru-Rh-Pd alloy in air flow the release rate of gaseous ruthenium oxides is reduced to 60-80% compared to the value measured in case of oxidation of pure metallic ruthenium powder in the same thermal-hydraulic conditions. Furthermore, if additional elements and chemical compounds representing other fission products were added in the alloy, a time delay of 30 to 60 min appeared in the release of gaseous ruthenium to the room-temperature environment. One of the main results was that in the outlet air flow reaching the environment the partial pressure of RuO4 was far above what could be expected for room-temperature equilibrium conditions. It was pointed out that the highly volatile RuO4 can decompose in solid, non-volatile RuO2 and O2. The X-ray fluorescence analysis results showed that some ruthenium compounds deposited on the colder circuit walls of the test facility. This suggests RuO4 is not fully airstable, i.e., its stability in air can be limited in time.JRC.F.4-Nuclear design safet

A comparative analysis of the causes of air pollution in three cities of the Danube region: implications for the implementation of the air quality directives

The causes of air pollution in three cities of the Danube region (Budapest, Sofia and Zagreb) were studied using datasets of measurements and modelling tools. The contributions from different activity sectors, including natural sources and their geographical origin were quantified. It was observed that most of the pollutants are emitted locally. However, the medium to long range transport may be also considerable. On the basis of the output of the source identification, a series of measures were proposed to deal wtih the pollution problem at local, national and international levels.JRC.H.2-Air and Climat

Three-year long source apportionment study of airborne particles in Ulaanbaatar using X-ray fluorescence and positive matrix factorization

The capital city of Mongolia, Ulaanbaatar, suffers from high levels of pollution due to excessive airborne particulate matter (APM). A lack of systematic data for the region has inspired investigation into the type, origin and seasonal variations of this pollution, the effects of meteorological conditions and even the time-dependence of anthropogenic sources. This work reports source apportionment results from a large data set of 184 samples each of fine (PM2.5) and coarse (PM2.5-10) fraction atmospheric PM collected over a three-year period (2014–2016) in Ulaanbaatar, Mongolia. Positive Matrix Factorization (PMF) was applied using the concentrations of 16 elements measured by an energy dispersive X-ray fluorescence spectrometer along with the black carbon content measured by a reflectometer as input data. The PMF results revealed that whereas mixed sources dominate the coarse fraction, soil and traffic sources are the principle contributors to the fine fraction. The source profiles and the seasonal variations of their contributions indicate that fly ash emanating from coal combustion mixes with traffic emissions and resuspended soil, resulting in variable chemical source profiles. Four sources were identified for both fractions, namely, soil, coal combustion, traffic and oil combustion, which respectively contributed 35%, 16%, 41% and 8% to the coarse fraction and 31%, 27%, 31% and 11% to the fine fraction. Additionally, the probable source contributions from long-range transport events were assessed via concentration-weighted trajectory analysis

Environmental Studies

With the political turmoil of the late 1960s the concern of human kind was shifted from passiv observer and sufferer of environmental problems to taking an active role in policy making.JRC.E.5-Nuclear chemistr

Experimental assessment of effectively probed volume in confocal XRF spectrometry using microparticles

Current approaches for assessing a confocal micro‐X‐rayfluorescence–probing volume involve the use of sharp knife edges, thin films, or wires, which are moved through this volume. The fluorescence radiation excited in the material of the object is measured, and profiles are built to enable the determination of the full width at half maximum in any of the three axes of the excited volume. Such approaches do not provide information on the shape of the volume, and the consequent alignment of both used lenses is made based on the position of the maxima of the registered intensity measurements. The use of particles that are smaller than the interaction volume (isolated enough to prevent the influence of nearby particles) and translated through the interaction volume (3D scan) is presented as an alternative methodology to determine the confocal probing volume. Spherical shaped uranium particles with diameter of 1–3 μm originally produced for scanning electron microscopy analysis calibration purposes were used in this study. The results obtained showed that the effectively probed confocal volume has a distinct prolate spheroidal shape that is longer in the axis of the confocal detector than it is wide on the axes of the plane perpendicular to it. The diameter in the longest axis (tilted accordingly to the angle between the two silicon drift detectors) was found to be approximately 25 μm, whereas the shorter was found about 15 μm each, with a volume of about 3,000 μm3

Sources and geographic origin of particulate matter in urban areas of the Danube macro-region: the cases of Zagreb (Croatia), Budapest (Hungary) and Sofia (Bulgaria)

The contribution of main PM pollution sources and their geographic origin in three urban sites of the Danube macro-region (Zagreb, Budapest and Sofia) were determined by combining receptor and Lagrangian models. The source contribution estimates were obtained with the Positive Matrix Factorization (PMF) receptor model and the results were further examined using local wind data and backward trajectories obtained with FLEXPART. Potential Source Contribution Function (PSCF) analysis was applied to identify the geographical source areas for the PM sources subject to long-range transport. Gas-to-particle transformation processes and primary emissions from biomass burning are the most important contributors to PM in the studied sites followed by re-suspension of soil (crustal material) and traffic. These four sources can be considered typical of the Danube macro-region because they were identified in all the studied locations. Long-range transport was observed of: a) sulphate-enriched aged aerosols, deriving from SO2 emissions in combustion processes in the Balkans and Eastern Europe and b) dust from the Saharan and Karakum deserts. The study highlights that PM pollution in the studied urban areas of the Danube macro-region is the result of both local sources and long-range transport from both EU and no-EU areas.JRC.C.5-Air and Climat

Quantification of Element Mass Concentrations in Ambient Aerosols by Combination of Cascade Impactor Sampling and Mobile Total Reflection X-ray Fluorescence Spectroscopy

Quantitative chemical analysis of airborne particulate matter (PM) is vital for the understanding of health effects in indoor and outdoor environments, as well as for enforcing EU air quality regulations. Typically, airborne particles are sampled over long time periods on filters, followed by lab-based analysis, e.g., with inductively coupled plasma mass spectrometry (ICP-MS). During the EURAMET EMPIR AEROMET project, cascade impactor aerosol sampling is combined for the first time with on-site total reflection X-ray fluorescence (TXRF) spectroscopy to develop a tool for quantifying particle element compositions within short time intervals and even on-site. This makes variations of aerosol chemistry observable with time resolution only a few hours and with good size resolution in the PM10 range. The study investigates the proof of principles of this methodological approach. Acrylic discs and silicon wafers are shown to be suitable impactor carriers with sufficiently smooth and clean surfaces, and a non-destructive elemental mass concentration measurement with a lower limit of detection around 10 pg/m3 could be achieved. We demonstrate the traceability of field TXRF measurements to a radiometrically calibrated TXRF reference, and the results from both analytical methods correspond satisfactorily

Quantification of Element Mass Concentrations in Ambient Aerosols by Combination of Cascade Impactor Sampling and Mobile Total Reflection X-ray Fluorescence Spectroscopy

Quantitative chemical analysis of airborne particulate matter (PM) is vital for the understanding of health effects in indoor and outdoor environments, as well as for enforcing EU air quality regulations. Typically, airborne particles are sampled over long time periods on filters, followed by lab-based analysis, e.g., with inductively coupled plasma mass spectrometry (ICP-MS). During the EURAMET EMPIR AEROMET project, cascade impactor aerosol sampling is combined for the first time with on-site total reflection X-ray fluorescence (TXRF) spectroscopy to develop a tool for quantifying particle element compositions within short time intervals and even on-site. This makes variations of aerosol chemistry observable with time resolution only a few hours and with good size resolution in the PM10 range. The study investigates the proof of principles of this methodological approach. Acrylic discs and silicon wafers are shown to be suitable impactor carriers with sufficiently smooth and clean surfaces, and a non-destructive elemental mass concentration measurement with a lower limit of detection around 10 pg/m3 could be achieved. We demonstrate the traceability of field TXRF measurements to a radiometrically calibrated TXRF reference, and the results from both analytical methods correspond satisfactorily

Source Term Identification of Environmental Radioactive Pu/U Particles by their Characterisation with Non-Destructive Analytical Techniques

Six radioactive particles stemming from Thule area (NW-Greenland) were investigated by gamma-ray and L X-ray spectrometry based on radioactive disintegration, scanning electron microscopy coupled with energy-dispersive and wavelength-dispersive X-ray spectrometer, synchrotron radiation based techniques as microscopic X-ray fluorescence, microscopic X-ray absorption near-edge structure (A-XANES) as well as combined X-ray absorption and fluorescence microtomography. Additionally, one particle from Mururoa atoll was examined by microtomography. From the results obtained, it was found out that the U and Pu were mixed in the particles. The U:Pu intensity ratios in the Thule particles varied between 0.05 and 0.36. The results from the microtomography showed that U:Pu ratio was not homogeneously distributed. The 241Am:238 239 240Pu activity ratios varied between 0.13 and 0.17, indicating that the particles originate from different source terms. The oxidation states of U and Pu as determined by A-XANES showed that U(IV) is the preponderant species and for Pu, two types of particles could be evidenced. One set had about 90 Pu(IV) while in the other the ratio Pu(IV):Pu(VI) was about one third.JRC.E.5-Nuclear chemistr