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

Methods for identifying high-redshift galaxy cluster candidates

Recent theories linked long gamma ray bursts (GRBs) to galaxies with rapid star formation or starburst; thus, we expect that long GRBs (LGRBs) are more frequent in midcluster galaxies where mergers and tidal interactions between gas-rich galaxies are more likely to occur. Yet there is no galaxy cluster known to be associated with LGRBs. We demonstrate that, based on deep, single-band Subaru Hyper Suprime-Cam observations, we may provide constraints on photometric redshifts of groups of galaxies. We compare three methods: cosmological approach, pseudoinverse matrix, and random forests to estimate galaxy and quasar redshifts. Comparing our results to spectroscopic redshifts of Sloan Digital Sky Survey's-detected extragalactic sources, random forests may provide the highest accuracy with as low as 17 percentage error. This is a powerful method to find clusters to place GRB host galaxies in their local environment

The Combination of Single-Cell and Next-Generation Sequencing Can Reveal Mosaicism for BRCA2 Mutations and the Fine Molecular Details of Tumorigenesis

Simple Summary Germline and somatic BRCA1/2 mutations may define therapeutic targets and refine cancer treatment options. However, routine BRCA diagnostic approaches cannot reveal the exact time and origin of BRCA1/2 mutation formation, and thus, the fine details of their contribution to tumor progression remain less clear. We established a diagnostic pipeline using high-resolution microscopy and laser microcapture microscopy to test for BRCA1/2 mutations in tumors at the single-cell level, followed by deep next-generation sequencing of various tissues from the patient. To demonstrate the power of our approach, here we present a detailed analysis of an ovarian cancer patient, in which we describe constitutional somatic mosaicism of a BRCA2 mutation. Characterization of the mosaic mutation at the single-cell level contributes to a better understanding of BRCA mutation formation and supports the concept that the combination of single-cell and next-generation sequencing methods is advantageous over traditional mutational analysis methods. Germline mutations in the BRCA1 and BRCA2 genes are responsible for hereditary breast and ovarian cancer syndrome. Germline and somatic BRCA1/2 mutations may define therapeutic targets and refine cancer treatment options. However, routine BRCA diagnostic approaches cannot reveal the exact time and origin of BRCA1/2 mutation formation, and thus, the fine details of their contribution to tumor progression remain less clear. Here, we establish a diagnostic pipeline using high-resolution microscopy and laser microcapture microscopy to test for BRCA1/2 mutations in the tumor at the single-cell level, followed by deep next-generation sequencing of various tissues from the patient. To demonstrate the power of our approach, here, we describe a detailed single-cell-level analysis of an ovarian cancer patient we found to exhibit constitutional somatic mosaicism of a pathogenic BRCA2 mutation. Employing next-generation sequencing, BRCA2 c.7795G>T, p.(Glu2599Ter) was detected in 78% of reads in DNA extracted from ovarian cancer tissue and 25% of reads in DNA derived from peripheral blood, which differs significantly from the expected 50% of a hereditary mutation. The BRCA2 mutation was subsequently observed at 17-20% levels in the normal ovarian and buccal tissue of the patient. Together, our findings suggest that this mutation occurred early in embryonic development. Characterization of the mosaic mutation at the single-cell level contributes to a better understanding of BRCA mutation formation and supports the concept that the combination of single-cell and next-generation sequencing methods is advantageous over traditional mutational analysis methods. This study is the first to characterize constitutional mosaicism down to the single-cell level, and it demonstrates that BRCA2 mosaicism occurring early during embryogenesis can drive tumorigenesis in ovarian cancer.Peer reviewe

Srs2 mediates PCNA-SUMO-dependent inhibition of DNA repair synthesis

Completion of DNA replication needs to be ensured even when challenged with fork progression problems or DNA damage. PCNA and its modifications constitute a molecular switch to control distinct repair pathways. In yeast, SUMOylated PCNA (S-PCNA) recruits Srs2 to sites of replication where Srs2 can disrupt Rad51 filaments and prevent homologous recombination (HR). We report here an unexpected additional mechanism by which S-PCNA and Srs2 block the synthesis-dependent extension of a recombination intermediate, thus limiting its potentially hazardous resolution in association with a cross-over. This new Srs2 activity requires the SUMO interaction motif at its C-terminus, but neither its translocase activity nor its interaction with Rad51. Srs2 binding to S-PCNA dissociates Polδ and Polη from the repair synthesis machinery, thus revealing a novel regulatory mechanism controlling spontaneous genome rearrangements. Our results suggest that cycling cells use the Siz1-dependent SUMOylation of PCNA to limit the extension of repair synthesis during template switch or HR and attenuate reciprocal DNA strand exchanges to maintain genome stability. © 2013 European Molecular Biology Organization

Oxidation and Release of Ruthenium from Short Fuel Rods above 1500oC

The fission product ruthenium is radiotoxic and in oxidized form as ruthenium-tetroxide (RuO4) also chemical toxic. During fuel element change or in case of a leakage in fuel storages, air flows in the containment or fuel storage. If the circulation pump fails, the fuel elements are heated-up, and at high temperatures gaseous ruthenium oxides are formed and rapidly released from the fuel. Due to the significant higher volatility of RuO4 in the Chernobyl Catastrophe the measured concentration of the Ru-isotopes in the fall-outs was comparable to those of iodine and caesium. In order to get more insight in the chemical and physical behaviour of this fission product under severe accident conditions, the Ruthenium release was studied in a series of Separate Effect Tests (RUSET). In the test short fuel rod segments were used and exposed to air and steam atmosphere at high temperatures. The experiments in air atmosphere showed, that the partial pressures of the released Ru-oxides was two orders of magnitudes lower compared to those measured in previous tests with Ru-powder diluted in a ZrO2 matrix. It was found that ruthenium was not released in steam atmosphere in the examined temperature range. Furthermore, the temperature dependence of the deposition was detected by XRF analysis.JRC.F.4-Nuclear design safet

Experimental investigation of the late phase of spent fuel pool accidents

Experimental programmes have been carried out in order to investigate the behaviour of nuclear fuel components in high-temperature air atmosphere, which characterises the main conditions of the late phase of spent fuel pool accidents. The tests provided new data on the oxidation of zirconium cladding in different atmospheres, on the oxidation and release of ruthenium from fuel pellets and on the integral behaviour of fuel bundles. The integral test confirmed that water injection into the spent fuel storage pool is the right measure to terminate a severe accident

Galactic foreground of gamma-ray bursts from AKARI Far-Infrared Surveyor

We demonstrate the use of the AKARI FIS All-Sky Survey maps in the study of extragalactic objects. A quick but reliable estimate of the Galactic foreground is essential for extragalactic research in general. We explored the galactic foreground and calculated hydrogen column densities using AKARI FIS and other recent all-sky survey data, and compared our results to former estimates. Our AKARI-FIS-based foreground values were then used toward gamma-ray burst (GRB) sources as input for X-ray afterglow spectrum fitting. From those fits the intrinsic column densities at the GRB sources were derived. The high-angular-resolution AKARI-FIS-based Galactic foreground hydrogen column densities are statistically very similar, but for most of the tested directions somewhat lower than previous estimates based on low-resolution data. This is due to the low filling factor of high-density enhancements in all galactic latitudes. Accordingly, our AKARI-FIS-based new intrinsic hydrogen column densities are usually higher or similar compared to the values calculated based, e.g., on the low-resolution Leiden/Argentine/Bonn survey data and listed in the Leicester database. The variation, however, is typically smaller than the error of the estimate from the fits of the X-ray afterglow spectra. There are a number of directions where the improvement of the foreground estimates resulted in an overestimate of magnitude or higher increment of the derived intrinsic hydrogen column densities. We concluded that most of the GRBs with formerly extremely low intrinsic hydrogen column densities are in fact normal, but we confirmed that GRB050233 is indeed a non- enveloped long GRB