Biogeochemical Cycling of 99Tc in Alkaline Sediments

99Tc will be present in significant quantities in radioactive wastes including intermediate-level waste (ILW). The internationally favored concept for disposing of higher activity radioactive wastes including ILW is via deep geological disposal in an underground engineered facility located ∼200–1000 m deep. Typically, in the deep geological disposal environment, the subsurface will be saturated, cement will be used extensively as an engineering material, and iron will be ubiquitous. This means that understanding Tc biogeochemistry in high pH, cementitious environments is important to underpin safety case development. Here, alkaline sediment microcosms (pH 10) were incubated under anoxic conditions under “no added Fe(III)” and “with added Fe(III)” conditions (added as ferrihydrite) at three Tc concentrations (10–11, 10–6, and 10–4 mol L–1). In the 10–6 mol L–1 Tc experiments with no added Fe(III), ∼35% Tc(VII) removal occurred during bioreduction. Solvent extraction of the residual solution phase indicated that ∼75% of Tc was present as Tc(IV), potentially as colloids. In both biologically active and sterile control experiments with added Fe(III), Fe(II) formed during bioreduction and >90% Tc was removed from the solution, most likely due to abiotic reduction mediated by Fe(II). X-ray absorption spectroscopy (XAS) showed that in bioreduced sediments, Tc was present as hydrous TcO2-like phases, with some evidence for an Fe association. When reduced sediments with added Fe(III) were air oxidized, there was a significant loss of Fe(II) over 1 month (∼50%), yet this was coupled to only modest Tc remobilization (∼25%). Here, XAS analysis suggested that with air oxidation, partial incorporation of Tc(IV) into newly forming Fe oxyhydr(oxide) minerals may be occurring. These data suggest that in Fe-rich, alkaline environments, biologically mediated processes may limit Tc mobility.Peer reviewe

The GALEX Ultraviolet Atlas of Nearby Galaxies

We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its far-ultraviolet (FUV; λ_(eff) = 1516 Å) and near-ultraviolet (NUV; λ_(eff) = 2267 Å) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate [SFR]) of galaxies in the local universe. From the surface brightness profiles obtained we have computed asymptotic magnitudes, colors, and luminosities, along with the concentration indices C31 and C42. We have also morphologically classified the UV surface brightness profiles according to their shape. This data set has been complemented with archival optical, near-infrared, and far-infrared fluxes and colors. We find that the integrated (FUV − K) color provides robust discrimination between elliptical and spiral/irregular galaxies and also among spiral galaxies of different subtypes. Elliptical galaxies with brighter K-band luminosities (i.e., more massive) are redder in (NUV − K) color but bluer in (FUV − NUV) (a color sensitive to the presence of a strong UV upturn) than less massive ellipticals. In the case of the spiral/irregular galaxies our analysis shows the presence of a relatively tight correlation between the (FUV − NUV) color (or, equivalently, the slope of the UV spectrum, β) and the total infrared-to-UV ratio. The correlation found between (FUV − NUV) color and K-band luminosity (with lower luminosity objects being bluer than more luminous ones) can be explained as due to an increase in the dust content with galaxy luminosity. The images in this Atlas along with the profiles and integrated properties are publicly available through a dedicated Web page

Microbial Degradation of Citric Acid in Low Level Radioactive Waste Disposal: Impact on Biomineralization Reactions

From Frontiers via Jisc Publications RouterHistory: received 2020-11-20, collection 2021, accepted 2021-03-10, epub 2021-04-28Publication status: PublishedOrganic complexants are present in some radioactive wastes and can challenge waste disposal as they may enhance subsurface mobility of radionuclides and contaminant species via chelation. The principal sources of organic complexing agents in low level radioactive wastes (LLW) originate from chemical decontamination activities. Polycarboxylic organic decontaminants such as citric and oxalic acid are of interest as currently there is a paucity of data on their biodegradation at high pH and under disposal conditions. This work explores the biogeochemical fate of citric acid, a model decontaminant, under high pH anaerobic conditions relevant to disposal of LLW in cementitious disposal environments. Anaerobic microcosm experiments were set up, using a high pH adapted microbial inoculum from a well characterized environmental site, to explore biodegradation of citrate under representative repository conditions. Experiments were initiated at three different pH values (10, 11, and 12) and citrate was supplied as the electron donor and carbon source, under fermentative, nitrate-, Fe(III)- and sulfate- reducing conditions. Results showed that citrate was oxidized using nitrate or Fe(III) as the electron acceptor at > pH 11. Citrate was fully degraded and removed from solution in the nitrate reducing system at pH 10 and pH 11. Here, the microcosm pH decreased as protons were generated during citrate oxidation. In the Fe(III)-reducing systems, the citrate removal rate was slower than in the nitrate reducing systems. This was presumably as Fe(III)-reduction consumes fewer moles of citrate than nitrate reduction for the same molar concentrations of electron acceptor. The pH did not change significantly in the Fe(III)-reducing systems. Sulfate reduction only occurred in a single microcosm at pH 10. Here, citrate was fully removed from solution, alongside ingrowth of acetate and formate, likely fermentation products. The acetate and lactate were subsequently used as electron donors during sulfate-reduction and there was an associated decrease in solution pH. Interestingly, in the Fe(III) reducing experiments, Fe(II) ingrowth was observed at pH values recorded up to 11.7. Here, TEM analysis of the resultant solid Fe-phase indicated that nanocrystalline magnetite formed as an end product of Fe(III)-reduction under these extreme conditions. PCR-based high-throughput 16S rRNA gene sequencing revealed that bacteria capable of nitrate Fe(III) and sulfate reduction became enriched in the relevant, biologically active systems. In addition, some fermentative organisms were identified in the Fe(III)- and sulfate-reducing systems. The microbial communities present were consistent with expectations based on the geochemical data. These results are important to improve long-term environmental safety case development for cementitious LLW waste disposal

Effect of groundwater pH and ionic strength on strontium sorption in aquifer sediments: Implications for 90Sr mobility at contaminated nuclear sites

Abstract Strontium-90 is a beta emitting radionuclide produced during nuclear fission, and is a problem contaminant at many nuclear facilities. Transport of 90 Sr in groundwaters is primarily controlled by sorption reactions with aquifer sediments. The extent of sorption is controlled by the geochemistry of the groundwater and sediment mineralogy. Here, batch sorption experiments were used to examine the sorption behaviour of Sr in contaminated sediments will remain primarily in weakly bound surface complexes. Therefore, if groundwater ionic strength increases (e.g. by saline intrusion related to sea level rise or by design during site remediation) then substantial remobilisation of 90 Sr is to be expected

Anaerobic biodegradation of citric acid in the presence of Ni and U at alkaline pH; impact on metal fate and speciation

Biodegradation of citrate occurred under LLW repository relevant conditions with Ni and U present. Citrate biodegradation led to the formation of insoluble Ni sulfides or nanocrystalline U(iv)–phosphate and may promote Ni/U retention in LLW repositories.</jats:p

Improving Together: A National Framework for Quality and GP Clusters in Scotland

Improving together will complement the development of the Scottish national GP contract that sets out the role of GPs and their important contribution as clinical leaders and expert medical generalists working in a community setting. This framework will be reviewed by the Scottish Government and the Scottish General Practitioners Committee of the BMA on a periodic basis, attentive to feedback from those involved in delivering its intent. As such, it is a framework that will develop to its full potential over time, as elements of the transformation of primary care in Scotland create the capacity to do so

The GALEX Ultraviolet Atlas of Nearby Galaxies

We present images, integrated photometry, surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the GALEX satellite in its far-ultraviolet (FUV; 1516A) and near-ultraviolet (NUV; 2267A) bands. (...) This data set has been complemented with archival optical, near-infrared, and far-infrared fluxes and colors. We find that the integrated (FUV-K) color provides robust discrimination between elliptical and spiral/irregular galaxies and also among spiral galaxies of different sub-types. Elliptical galaxies with brighter K-band luminosities (i.e. more massive) are redder in (NUV-K) color but bluer in (FUV-NUV) than less massive ellipticals. In the case of the spiral/irregular galaxies our analysis shows the presence of a relatively tight correlation between the (FUV-NUV) color and the total infrared-to-UV ratio. The correlation found between (FUV-NUV) color and K-band luminosity (with lower luminosity objects being bluer than more luminous ones) can be explained as due to an increase in the dust content with galaxy luminosity. The images in this Atlas along with the profiles and integrated properties are publicly available through a dedicated web page at http://nedwww.ipac.caltech.edu/level5/GALEX_Atlas/Comment: 181 pages, 10 figures, accepted for publication in ApJS (abstract abridged

Influence of Hyper-Alkaline pH Leachate on Mineral and Porosity Evolution in the Chemically Disturbed Zone Developed in the Near-Field Host Rock for a Nuclear Waste Repository

This paper evaluates the effect of hyper-alkaline (NaOH/KOH) leachate on the mineralogy and porosity of a generic quartzo-feldspathic host rock for intermediate- and low-level nuclear waste disposal following permeation of the cementitious repository barrier by groundwater. The analysis is made with reference to expected fluid compositions that may develop by contact of groundwater with the cementitious barrier to form a chemically disturbed zone (CDZ) in the adjacent host rock, as informed by relevant natural analogue sites. Theoretical analysis and numerical modelling is used to explore the influence of different host rock mineral assemblages on changes in pore fluid chemistry, multiple mineral dissolution and precipitation reactions and matrix porosity within the CDZ under these conditions. The numerical modelling accounts for kinetic and surface area effects on the mineral transformation and porosity development for periods of up to 10,000 years travel time from the repository and ambient temperature of 20∘C. The analysis shows that dissolution of quartz, feldspar and muscovite in the host rock, by the hyper-alkaline waste leachate, will create relatively high concentrations of dissolved Si and Al in the pore fluid, which migrates as chemical fronts within the CDZ. Precipitation of secondary mineral phases is predicted to occur under these conditions. The increase in matrix porosity that arises from dissolution of primary aluminosilicate minerals is compensated by a reduction in porosity due to precipitation of the secondary phases, but with a net overall increase in matrix porosity. These coupled physical and geochemical processes are most important for contaminant transport in the near-field zone of the CDZ and are eventually buffered by the host rock within 70 m of the repository for the 10,000 year travel time scenario. The predicted changes in matrix porosity may contribute to increased transport of radionuclides in the host rock, in the absence of attenuation by other mechanisms in the CDZ