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Biogenic Mn oxides are reactive and ubiquitous in many Earth surface environments, yet their role in radionuclide sequestration at U mill-tailings sites still require an improved understanding at the nano- and molecular-scales. This study concerns the uptake of Ba, utilized as a safe and chemically appropriate surrogate for radioactive Ra, by biogenic Mn oxides produced by a fungal species, Coprinopsis urticicola, isolated from the mine water of the Ningyo-toge U mine, Okayama, Japan. The biogenic Mn oxides were identified as birnessite nanocrystals O binding to the newly overlying MnO6 layer during coprecipitation. Static desorption experiments for 7 days reveal that the steady-state release rate of adsorbed Ba is ∼1.4 times faster than that of the coprecipitated Ba, when the Ba concentration in the initial loading solution was ∼10–8 mol/L, indicating that the release of intercalated (coprecipitation) Ba to solution is retarded. The present study demonstrates the importance of fungus-generated Mn oxides as an efficient absorber of Ba2+, and likely Ra2+, among soil compounds in U mill-tailings. This may be applicable to other contaminated sites due to the ubiquitous occurrence of fungi in the environment.

The accident at the Fukushima Daiichi Nuclear Power Plant in 2011 released many radioactive elements into the environment, contaminating a large amount of soil. Currently, 14 million m3 of contamin...

Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium. To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn

Ferrihydrite, a hydrous ferric oxide, is ubiquitous in silica-rich mine drainage sites, although some uncertaity remains concerning its nanoscale texture and colloidal properties such as its association with amorphous silica and reactions with contaminant metals. To understand the mechanisms of natural attenuation of contaminants governed by ferrihydrite and amorphous silica aggregations, mine tailings material from the Ningyo-toge uranium deposit, Japan, has been investigated in detail utilizing many traditional solution and mass spectroscopy methods, as well as synchrotron-based methods the latest in FIB- and analytic TEM-based technologies. At this site, the past mining activity results in slightly acidic mine drainage and the contamination of a mill tailings pond with relatively high concentrations of toxic elements, including U, As, and Ra. We have systematically investigated the geochemistry of water, colloids, and sediments from the groundwater draining the former mine site (now remediated), down gradient to the mill tailings pond where the water pH remains ∼6.2. Groundwater with 0.18 mg/L dissolved oxygen (DO) is oxygenated rapidly to levels of 1.65 mg/L DO when exposed to the atmosphere along this flow path. Dissolved Fe2+ is oxidized instantly to form ferrihydrite nanoparticle aggregates > 200 nm in diameter, adsorbing ∼67% of the total As (3.36 µmol/L) in solution. For solutions and particles/aggregates passing through 200-nm filters, ∼17% of the 1.17 µmol/L As is sorbed on these smaller ferrihydrite aggregates. Simultaneously, varying amounts of amorphous silica with particle sizes as small as several nanometers were observed to adsorb onto ferrihydrite aggregates. Arsenic is present predominantly as arsenate, As(V), and preferentially adsorbs to ferrihydrite within these ferrihydrite–amorphous silica aggregates. Arsenate adsorption is not inhibited by silica adsoption on ferrihydrite when the Si/Fe composition is ∼0.25. Uranium is also adsorbed onto aggregates of colloids. After 24 h of static exposure to the ambient atmosphere, the zeta potential of the aggregate that formed in oxygenated water decreases from −16 to −24 mV, near the zeta potential of pure silica, potentially leading to increased colloidal stability. Some large-sized aggregates are deposited at the bottom of the collecting well and slowly adsorb minor amounts of Mn (1.45 wt.%); other aggregates are transported to the mill tailings pond downsteam, where the water is further oxidized (DO = 3.09 mg/L), and deposited onto the sediment together with birnessite, a hydrated Mn-oxide that appears to be biogenic in this case. During sedimentation, associations of amorphous silica within the aggregate play a key role in retaining the ferrihydrite structure that adsorbs toxic elements such as As. Consequently, the mechanism of natural attenuation at the nanoscale constrained by the chemical and physical properties of ferrihydrite–amorphous silica aggregates is of critical importance in the Ningyo-toge mill tailing site. It is shown that it is also important in other mine drainage and mill tailings sites due to the ubiquitous and dominant occurrence of both Si and Fe in these types of settings.

This article investigates metallization-induced recombination losses associated with the presence of silicon (Si) in the 1) rear passivation layers and 2) aluminum (Al) paste in fully screen-printed p -type passivated emitter and rear cell (PERC) solar cells. For 1), the rear sides of PERCs passivated with aluminum oxide films stacked with silicon nitride (SiN y ) films with various refractive indexes (n), as defined by the composition of the SiN y films, were fabricated. Si-rich SiN y films strongly degraded the implied open-circuit voltages of symmetrically passivated samples, that include cells. Elemental mapping analysis confirmed further metallization-induced losses at the cell level because of the formation of an Al-Si alloy within the passivation stacks, with the density of the alloy dependent on the refractive index. For 2), the rear sides of PERCs were metallized with Si-free Al paste or Al pastes that contain Si. High-Si paste had both good and bad effects: it produced thicker aluminum back surface fields but left partially-formed Al-Si alloy within the passivation films.

Calcium molybdate nanoparticles were synthesized using a liposome based on egg phosphatidylcholine and cholesterol. The molybdate ion was encapsulated into the liposome, and then a calcium chloride...

Boron carbide control rods remain in the fuel debris of the damaged reactors in the Fukushima Daiichi Nuclear Power Plant, potentially preventing re-criticality; however, the state and stability of the control rods remain unknown. Sensitive high-resolution ion microprobe analyses have revealed B-Li isotopic signatures in radioactive Cs-rich microparticles (CsMPs) that formed by volatilization and condensation of Si-oxides during the meltdowns. The CsMPs contain 1518-6733 mg kg

Following identification of radioactive Cs microparticles (CsMPs) in aerosol samples from the Fukushima Daiichi Nuclear Power Plant (FDNPP), numerous reports on CsMPs have been published. This pape...

In order to achieve the highly efficient 99mTc production from 100MoO3 by the 100Mo(n, 2n)99Mo reaction, we have developed a new protocol to synthesize nano-sized Mo particles, of which the size was controlled by the inner space of the liposomes. Calcium and molybdate ions were encapsulated into ∼100 nm size liposomes. The liposome suspensions were then mixed and heated to promote the membrane fusion. As a result, the insoluble CaMoO4 nanoparticles precipitated inside the liposomes. The median particle diameter of 168 nm and average diameter of 169 ± 56 nm (n = 109) were obtained from an SEM image, and the particles have a powellite-structure. The formation process of the particles was then examined. The formation of nano-sized CaMoO4 was observed by the high resolution TEM image and TEM image of negative-stained liposome. At the room temperature, the fusion of liposome did not occur significantly. These results suggest that nanocrystals of the CaMoO4 were likely formed in the liposomes because of the liposome fusion and aggregated during the drying processes of reaction solution.

This paper presents the development of industrial-sized p-type passivated emitter and rear cells (PERCs) with a selective emitter (SE) structure. We focus on different assisted passivation schemes and use nitric acid oxidation of silicon (NAOS) to form an ultrathin SiO2 layer. The results show that all I–V parameters of the PERCs are significantly modified when SiO2 is present on the front and/or rear sides of the cell. For front-emitter passivation by NAOS-SiO2, we observe an increase in the open-circuit voltage (Voc) and short-circuit current density (Jsc) and strong enhancement of the internal quantum efficiency (IQE) for short-wavelength photons. This can be attributed to the high level of chemical passivation, as indicated by the reduced interface trap density (Dit), due to the reduced Shockley–Read–Hall recombination. By contrast, all I–V parameters associated with SiO2 rear passivation decrease due to the increased Dit, which results in enhanced surface recombination. The different types of surface passivation for n-type (front) and p-type (rear) surfaces are presumably due to different doping surface concentrations. These results suggest that NAOS surface pretreatment is a very promising technique to improve the level of surface passivation and thereby enhance the performance of industrial-sized PERCs.

Behavior of radiocesium in Fukushima after its deposition is mainly controlled by mobility of soil components, of which the density is one of the parameters governing the mobility; however, little information is available on the density of soil components associated with radiocesium in environment. Furthermore, the reduction of the volume of radiocesium-contaminated soil in the interim storage is highly demanded. In this study, we developed a gravitational separation method using a sodium polytungstate (SPT) solution combined with size fractionation to understand the relation between

International audience; Following the NPP accident, several hundred tons of heat-generating corium and fuel debris have been cooled permanently by millions of m3 of flowing. Knowledge on the interaction with water is crucial for any decommissioning planning.Starting from knowledge on the evolutions of the accident in the three reactor cores and associated fuel debris formations and some additional isotopic and physio-chemical information on debris fragments collected in Fukushima soils, we review the temporal evolution of the chemistry and leached radionuclide contents of the cooling water, comparing measured concentration ratios of the actinides and fission products in the water to reported results of laboratory leaching studies with either spent nuclear fuel or simulated fuel debris.As for spent fuel leaching, the fractions of inventories of 134,137Cs in the cooling water are orders of magnitude larger than that of the actinides. After more than 10 years of fuel debris/water contact, 137Cs release rates have decreased by about a factor of 100. The total release of actinides from the fuel debris is orders of magnitude lower than that of 134,137Cs or of 90Sr. This high stability makes direct disposal of fuel debris in suitable containers after decommissioning a viable option.

Understanding the long-term fate, stability, and bioavailability of uranium (U) in the environment is important for the management of nuclear legacy sites and radioactive wastes. Analysis of U behavior at natural analogue sites permits evaluation of U biogeochemistry under conditions more representative of long-term equilibrium. Here, we have used bulk geochemical and microbial community analysis of soils, coupled with X-ray absorption spectroscopy and mu-focus X-ray fluorescence mapping, to gain a mechanistic understanding of the fate of U transported into an organic-rich soil from a pitchblende vein at the UK Needle's Eye Natural Analogue site. U is highly enriched in the Needle's Eye soils (similar to 1600 mg kg(-1)). We show that this enrichment is largely controlled by U(VI) complexation with soil organic matter and not U(VI) bioreduction. Instead, organic-associated U(VI) seems to remain stable under microbially-mediated Fe(III)-reducing conditions. U(IV) (as non-crystalline U(IV)) was only observed at greater depths at the site (>25 cm); the soil here was comparatively mineral-rich, organic-poor, and sulfate-reducing/methanogenic. Furthermore, nanocrystalline UO2, an alternative product of U(VI) reduction in soils, was not observed at the site, and U did not appear to be associated with Fe-bearing minerals. Organicrich soils appear to have the potential to impede U groundwater transport, irrespective of ambient redox conditions. (C) 2020 The Authors. Published by Elsevier Ltd.

We propose a physical mechanism that explains the local contact formation stimulated by the aluminum-silicon (Al-Si) interdiffusion within the various widths of Al rear grid for bifacial-passivated emitter and rear cell (Bi-PERC). The rear sides of Bi-PERCs were screen-printed with thin fingers (< 100 μm) or wider fingers aligned directly on the contact sites. From the elemental mapping analysis results, the following conjecture was confirmed: rear metallization structure has a direct impact on the local contact formation, particularly on the thickness of aluminum-back surface field (Al-BSF), and microstructures of alloy formed. A thicker Al-BSF partly results in an increase in open-circuit voltage of Bi-PERC. The wider Al finger leads to a slight improvement in fill factor of a cell.

Understanding migration of radionuclides in subsurface environments is of critical importance to risk assessment at nuclear legacy sites. The chapters in this volume cover various phenomena in the groundwater system around the area of Lake Karachai of the Mayak Production Association site and highlight the important role of microorganisms and naturally occurring nanoparticles in the migration of radionuclides. In particular, knowledge regarding microbial ecology in subsurface environments, which may affect geochemical conditions in the system such as denitrification, has increased greatly during the last two decades. Based on the results of field observations and laboratory experiments, it is necessary to incorporate functions of microbial activity, groundwater colloids, and their interactions into a comprehensive model of radionuclides migration in the contaminated subsurface environment.

Plutonium association and transport by ferrihydrite has been confirmed in the groundwater system of Lake Karachai at the Mayak Production Association, Russia (Novikov et al. 2006). Since this initial description, there has been substantial progress in understanding the mechanisms that control the concentrations and distribution of Pu at the Mayak site. This chapter is a concise review of work during the past 10 years that utilizes to advantage recent advances in nanoscale, analytical techniques. The structure of ferrihydrite (P63mc) was determined using a pair-distribution function analysis. Scanning transmission electron microscopy of Mayak colloids resolved the occurrence of mixed silica nano-colloids and ferrihydrite. Thermodynamic properties for aqueous Pu-species have been updated. Inner-sphere surface complexation was determined for adsorbed Pu using synchrotron-based X-ray absorption spectroscopy. The adsorbed Pu can transform into Pu-dioxide nanoparticles as revealed by high-resolution transmission electron microscopy. Plutonium polymerization can also proceed by aggregation of cubic Pu-dihydroxy building blocks of Pu(OH)22+•6H2O. Plutonium desorption occurs associated with re-adsorption at neutral pH. To establish comprehensive model of Pu transport at the Mayak site, the detailed mechanisms described above must be considered. Rigorous characterization of colloids is necessary and these results must be compared with results obtained from experimental studies. The state-of-the-art knowledge on the Pu association with Fe hydroxides is now well enough understood that safety assessments no longer need to rely on the classical Kd approach.

High nitrate concentration together with high salinity of the groundwater in the area of Lake Karachai may enhance the activity of halophilic and denitrifying microorganisms. Those microorganisms affect transformation of chemical species of radionuclides through the function of cellular compounds as carboxyl and phosphoryl functional groups. Coordination environments of biosorbed Eu(III) by Halomonas sp. and P. denitrificans measured by time-resolved laser-induced fluorescence spectroscopy (TRLFS) showed that Eu(III) was coordinated with the functional groups. Even though clay mineral kaolinite is well known to adsorb cationic metal ions, SEM-EDS and TEM-EDS analyses of the U- and Pu-accumulated mixture of B. subtilis cells and kaolinite from the solution containing UO22+ and PuO22+ revealed that most of U and Pu were associated with B. subtilis cells in the mixtures. These results show that microbial cells possess higher sorption ability of U(VI) and Pu(VI) than clay mineral of kaolinite. U(VI) and trivalent actinides (An(III)) formed U(VI)- and An(III)-phosphate minerals on the cell surface of microorganisms. This mineralization resulted from post-sorption process, where U(VI) and An(III) were instantaneously sorbed on the cell surfaces of microorganisms, followed by the reaction with essential element of P released from the yeast to form U(VI)- and An(III)-phosphate minerals. During the formation of biological carbonate mineralization, coprecipitation of radionuclides is another process for retarding migration of actinides and Sr. Unicellular fungus yeast Saccharomyces cerevisiae accumulated radioactive Cs inside cells. Therefore, microorganisms play an important role for the migration of radionuclides including actinides in groundwater around Lake Karachai.

Minerals form in all types of chemical and physical environments [...]

Microorganisms play an important role in the mineralization of heavy metals in different environments. Previous studies have reported the phosphate mineralization of light (Ce) and heavy (Yb) rare earth elements with yeast. However, little is known about differences in the biomineralization process of middle rare earth elements (including Sm, Eu, Gd, Tb and Dy) by yeast and bacteria. We carried out a series of experiments to compare the sorption process of Sm by Saccharomyces cerevisiae (yeast), Pseudomonas fluorescens (gram-negative bacteria) and Bacillus subtilis (gram-positive bacteria) in initial pH 3, 4 and 5 solutions. The concentrations of Sm in exposure solutions decreased as a function of exposure time in all three systems, which revealed the accumulation of Sm by cells. In both yeast and bacteria systems, Sm(III) was mineralized to monazite(Sm) phase particles on cell surfaces at 5 days of exposure after a short-term adsorption process. In these three systems, nano-sized Sm phosphate formed more quickly on cell surfaces with higher pH exposure solutions. The formation of precipitation on bacterial cell surfaces was faster than in yeast. There were no significant differences in the sorption process of Sm between the two bacteria Pseudomonas fluorescens and Bacillus subtilis.

In light of the widespread Cs pollution that may follow nuclear disasters, the decontamination of post-accident soil has earned much attention due to the difficulty of Cs removal for its super-retention in micaceous minerals. Herein, we successfully used solvated Mg2+ to desorb Cs from Cs-saturated vermiculitized biotite (VB) to clarify the microscale mechanism underlying a Cs removal process, and we applied this new method to actual radioactive soil to validate the practical remediation effect. The results revealed that sorbed Cs was uniformly fixed in the collapsed interlayers of VB crystals and thus was poorly and slowly desorbed by ambient treatment with Mg2+ regardless of the treating concentration, duration time, and number of cycles. However, almost all Cs was effectively and efficiently removed by hydrothermal treatment at 250°C. Further characterizations of treated Cs-VB confirmed that Mg2+ indeed diffused into Cs collapsed interlayers from the edge-side to the interior central region with the increase of the treating temperature, and the substituted anhydrous Cs+ ensuing interlayer decollapsed. Similarly, a negligible amount of Cs was removed from the radioactive soil by treatment with Mg2+ at 60 °C, whereas nearly complete Cs removal was achieved at 250 °C, which clearly validated the desorption process as achieved for Cs-VB and definitely reinforced the applicability of the current reported pathway for practical Cs decontamination with soil remediation.

This paper introduces a selective phosphorus emitter formed by screen-printed resist masking combined with a wet chemical etch-back process for an industrial-sized passivated emitter and rear cell (PERC). Applying the selective emitter (SE) concept is expected to decrease the recombination losses at the front surface of the PERC cell. With the SE structure, we observed an increase in the open-circuit voltage $(V_{{\rm{oc}}})$ and short-circuit current density $(J_{{\rm{sc}}})$ , but a decrease in the fill factor (FF), compared with homogeneous emitter cells. The sheet resistance $(R_{{\rm{sheet}}})$ of the lightly doped emitter (n+-emitter) by the etch-back process had a considerable impact on the $V_{{\rm{oc}}}$ and $J_{{\rm{sc}}}$ , which we attributed to the reduced emitter saturation current density $(J_{0e})$ caused by a reduction in the Auger recombination in the n+ -emitter. The diminished FF was owing to the higher $R_{{\rm{sheet}}}$ , resulting in an increased series resistance of the cell. These results suggest that an SE structure made by the wet etch-back process is a very promising technology to improve the conversion efficiency of industrial-sized PERC solar cells.

We attempted to improve the performance of passivated emitter and rear cells by increasing the quality of the aluminum back surface field (Al-BSF) beneath the local contact. We demonstrate that a thicker Al-BSF can be obtained by adding Si to the screen-printing Al paste, offering a greater penetration depth of several micrometers compared to the silicon-free Al paste, thereby increasing the open-circuit voltage. The presence of Si in the Al paste is believed to suppress the driving force for the strong lateral Si diffusion toward the Al layer during alloying, as evidenced by 50% decrease in the penetration depth of the Al–Si melt. The electron probe microanalyzer element analysis indicates that the Si-free Al paste produced the combination of hypo- and hypereutectic structures, while the use of the Al paste containing Si resulted in a hypoeutectic alloy, which has a strong presence of the primary α -Al dendrites. Different BSF thicknesses can be explained by that the liquid Al containing Si within the openings is saturated faster than the Si-free Al liquid under the same conditions. These findings allow a better understanding of the mass transport phenomena stimulated by the diffusion of Si and Al during the alloying process.

International audience; A contaminated zone elongated toward Futaba Town, north-northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains highly radioactive particles released from reactor Unit 1. There are uncertainties associated with the physio-chemical properties and environmental impacts of these particles. In this study, 31 radioactive particles were isolated from surface soils collected 3.9 km north-northwest of the FDNPP. Two of these particles have the highest particle-associated 134+137Cs activity ever reported for Fukushima (6.1 × 105 and 2.5 × 106 Bq per particle after decay-correction to March 2011). The new, highly-radioactive particle labeled FTB1 is an aggregate of flaky silicate nanoparticles with an amorphous structure containing ~0.8 wt% Cs, occasionally associated with SiO2 and TiO2 inclusions. FTB1 likely originates from the reactor building, which was damaged by a H2 explosion, after adsorbing volatilized Cs. The 134+137Cs activity in the other highly radioactive particle labeled FTB26 exceeded 106 Bq. FTB26 has a glassy carbon core and a surface that is embedded with numerous micro-particles: Pb–Sn alloy, fibrous Al-silicate, Ca-carbonate or hydroxide, and quartz. The isotopic signatures of the micro-particles indicate neutron capture by B, Cs volatilization, and adsorption of natural Ba. The composition of the micro-particles on FTB26 reflects the composition of airborne particles at the moment of the H2 explosion. Owing to their large size, the health effects of the highly radioactive particles are likely limited to external radiation during static contact with skin; the highly radioactive particles are thus expected to have negligible health impacts for humans. By investigating the mobility of the highly radioactive particles, we can better understand how the radiation dose transfers through environments impacted by Unit 1. The highly radioactive particles also provide insights into the atmospheric conditions at the time of the Unit 1 explosion and the physio-chemical phenomena that occurred during reactor meltdown.

Highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) provide nano-scale chemical fingerprints of the 2011 tragedy. U, Cs, Ba, Rb, K, and Ca isotopic ratios were determined on three CsMPs (3.79–780 Bq) collected within ~10 km from the FDNPP to determine the CsMPs’ origin and mechanism of formation. Apart from crystalline Fe-pollucite, CsFeSi2O6 · nH2O, CsMPs are comprised mainly of Zn–Fe-oxide nanoparticles in a SiO2 glass matrix (up to ~30 wt% of Cs and ~1 wt% of U mainly associated with Zn–Fe-oxide). The 235U/238U values in two CsMPs: 0.030 (±0.005) and 0.029 (±0.003), are consistent with that of enriched nuclear fuel. The values are higher than the average burnup estimated by the ORIGEN code and lower than non-irradiated fuel, suggesting non-uniform volatilization of U from melted fuels with different levels of burnup, followed by sorption onto Zn–Fe-oxides. The nano-scale texture and isotopic analyses provide a partial record of the chemical reactions that occurred in the fuel during meltdown. Also, the CsMPs were an important medium of transport for the released radionuclides in a respirable form.

The sorption of Np(V) by microbe consortia and by a single pure culture of the Fe-reducing bacterium Shewanella putrefaciens was studied at pH levels between 3 and 7 under resting cell conditions. The sorption of Np(V) by S. putrefaciens obtained under inert conditions and by the consortia in the aerated condition was higher than that by S. putrefaciens under aerobic conditions at low pH below 5, strongly suggesting the presence of another mechanism other than the adsorption of Np(V) on the microbial cell surface, i.e., by reduction to Np(IV).

The impact of the post-implantation annealing conditions on the electrical characteristics of P-implanted homogeneous emitter silicon solar cells with aluminum-back surface field, 156 mm × 156 mm in size, is investigated. Based on a measurement of the internal quantum efficiency (IQE) and scanning capacitance microscopy observation, we discuss the behavior of the phosphorous prepared by annealing in a nitrogen atmosphere (PIA) and oxidation (PIO) after implantation of P and its impact on the cell characteristics. Implantation of P with step rotation was implemented while wafer made one rotation. A uniform thickness amorphous layer was formed in each side wall of the texture. The $\boldsymbol{p}$ - $\boldsymbol{n}$ junction depth of a P-implanted emitter with PIO is deeper than that of an emitter with PIA. Sheet resistance of P-implanted emitter with PIO shows higher value compared to that of PIA. The solar cell with PIO indicated a higher IQE at shorter wavelength. Solar cells with PIO show an improvement in the short-circuit current, open-circuit voltage, and conversion efficiency compared to cells subjected to PIA. A maximum conversion efficiency of 19.41% was obtained.

A representative gold(III) complex ion ([AuCl4]−), successively hydrolyzes to form [AuCl4−n(OH)n]− (n = 0–4) in aqueous solution as the pH increases and, finally, precipitates. It has been referred...

To understand the chemical durability of highly radioactive cesium-rich microparticles (CsMPs) released from the Fukushima Daiichi Nuclear Power Plant in March 2011, we have, for the first time, performed systematic dissolution experiments with CsMPs isolated from Fukushima soils (one sample with 108 Bq and one sample with 57.8 Bq of Cs-137) using three types of solutions: simulated lung fluid, ultrapure water, and artificial sea water, at 25 and 37 degrees C for 1-63 days. The Cs-137 was released rapidly within three days and then steady-state dissolution was achieved for each solution type. The steady-state Cs-137 release rate at 25 degrees C was determined to be 4.7 x 10(3), 1.3 x 10(3), and 1.3 x 10(3) Bq . m(-2)s(-1) for simulated lung fluid, ultrapure water, and artificial sea water, respectively. This indicates that the simulated lung fluid promotes the dissolution of CsMPs. The dissolution of CsMPs is similar to that of Si-based glass and is affected by the surface moisture conditions. In addition, the Cs release from the CsMPs is constrained by the rate-limiting dissolution of silicate matrix. Based on our results, CsMPs with similar to 2 Bq, which can be potentially inhaled and deposited in the alveolar region, are completely dissolved after >35 years. Further, CsMPs could remain in the environment for several decades; as such, CsMPs are important factors contributing to the long-term impacts of radioactive Cs in the environment. (C) 2019 Elsevier Ltd. All rights reserved.

Metaschoepite is commonly found in U-contaminated environments and metaschoepite-bearing wastes may be managed via shallow or deep disposal. Understanding metaschoepite dissolution and tracking the fate of any liberated U is thus important. Here, discrete horizons of metaschoepite (UO3 center dot nH(2)O) particles were emplaced in flowing sediment/groundwater columns representative of the UK Sellafield Ltd. site. The column systems either remained oxic or became anoxic due to electron donor additions, and the columns were sacrificed after 6- and 12-months for analysis. Solution chemistry, extractions, and bulk and micro/nano-focus X-ray spectroscopies were used to track changes in U distribution and behavior. In the oxic columns, U migration was extensive, with UO22+ identified in effluents after 6-months of reaction using fluorescence spectroscopy. Unusually, in the electron-donor amended columns, during microbially mediated sulfate reduction, significant amounts of UO2-like colloids (>60% of the added U) were found in the effluents using TEM. XAS analysis of the U remaining associated with the reduced sediments confirmed the presence of trace U(VI), noncrystalline U(IV), and biogenic UO2, with UO2 becoming more dominant with time. This study highlights the potential for U(IV) colloid production from U(VI) solids under reducing conditions and the complexity of U biogeochemistry in dynamic systems.

International audience; The abundance and distribution of highly radioactive cesium-rich microparticles (CsMPs) that were released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) during the first stage of the nuclear disaster in March 2011 are described for 20 surface soils collected around the FDNPP. Based on the spatial distribution of the numbers (particles/g) and radioactive fraction (RF) of the CsMPs in surface soil, which is defined as the sum of the CsMP radioactivity (in Bq) divided by the total radioactivity (in Bq) of the soil sample, three regions of particular interest have been identified: i.) near-northwest (N-NW), ii.) far-northwest (F-NW), and iii.) southwest (SW). In these areas, the number and RF of CsMPs were determined to be 22.1–101 particles/g and 15.4–34.0%, 24.3–64.8 particles/g and 36.7–37.4%, and 0.869–8.00 particles/g and 27.6–80.2%, respectively. These distributions are consistent with the plume trajectories of material released from the FDNPP on March 14, 2011, in the late afternoon through to the late afternoon of March 15, 2011, indicating that the CsMPs formed only during this short period. Unit 3 is the most plausible source of the CsMPs at the beginning of the release based on an analysis of the sequence of release events. The lower RF values in the N-NW region indicate a larger influence from subsequent plumes that mainly consisted of soluble Cs species formed simultaneously with precipitation. The quantitative map of the distribution of CsMPs provides an important understanding of CsMP dispersion dynamics and can be used to assess risks in inhabited regions.

We present metal-induced recombination losses associated with the silicon (Si) present both within rear passivation layers and in aluminum (Al) paste for passivated emitter and rear cells (PERCs) with full-area Al screen-printed contacts. In the former case, rear sides of PERCs passivated with aluminum oxide films stacked with silicon nitride (SiNy) films with various refractive indexes (n) defined by the composition of the SiNy films, were fabricated. As a result, the Si-rich SiNy films strongly degraded the open-circuit voltage of the cells. The elemental mapping analysis results clearly confirmed metal-induced further losses in cell level due to the concentration of an Al–Si alloy formed in the passivation stacks, where the density of the alloy is dependent on the refractive index. In the latter case, the rear sides of the PERCs were metallized with two different Al PERC pastes: 0% Si, or 25% Si. The resulting strong presence of Si in the Al paste gave both positive results owing to a thicker aluminum-back surface field and negative results owing to the partially formed Al–Si alloy within the passivation films.

The Ninth Symposium on Polar Science/Interdisciplinary sessions: [ID] Polar science developed by leading-edge analytical technology ～Beyond the micro meters and micro grams～, Thu. 6 Dec. / 3F Seminar room, National Institute of Polar Research

The high stability of zirconium dioxide in aqueous environments is known and demonstrated, and this property is strongly used in nuclear industry to ensure the long term storage of wastes. However, only upper limits of its aqueous solubility are known reliably and lower limits linked to very well crystallized ZrO2 are much less assessed. Indeed, the low dissolution rate of zirconia makes the solubility measurements a challenging task. To overcome, high S/V ratios of nanoparticles zirconia were used. This work also improved the sensitivity of analytical techniques (HR ICP-MS) and methodologies, and a reliable experimental procedure was developed to measure zirconium (quantification limit ≈10−11 mol∙L−1). New Zr(IV) dioxide solubility data at pH between 0 and 2 were obtained approaching solubility from under-saturated conditions in (Na,H)Cl and (Na,H)ClO4 medium. Two crystalline nanoparticle structures were compared: monoclinic and yttrium stabilized cubic zirconia. Very low solubility was measured for monoclinic phase between pH 1.5 and 2: between (1.8±1.2) × 10−10 mol∙L−1 at pH 2 and (2.3±1.0) × 10−10 mol∙L−1 at pH 1.5. The cubic zirconia showed higher solubility. Integrating the effect of ionic strength, particle size and aqueous speciation, solubility constants of log K s 0 = (-8.43±0.69) for the monoclinic nanoparticles and log K s 0 = (-7.12±0.35) for the yttrium stabilized cubic nanoparticles were obtained. High-resolution techniques (HR-TEM, SAXS and STEM-HAADF) were also used to assess the evolution of morphology and surface before, during and at equilibrium. Analysis of these results shows that the morphology and surface of nanoparticles in the raw state and after reaching equilibrium in (Na,H)Cl and (Na,H)ClO4 medium are similar.

It is known that cesium ion, Cs+, is strongly sorbed to micaceous minerals. However, the desorption of Cs+ at a trace sorption level with time in the presence of different salt ions is not well understood. In this study, we conducted long-term sorption and desorption experiments of Cs+ with illite and vermiculite at room temperature to study the effects of sorption time and co-existing cations on the desorption. A small amount of Cs+ (50 nM Cs+ spiked with 900 Bq 137Cs) was sorbed to the illite and vermiculite in the presence of 1 mM K+ or Ca2+, or 1 mM K+ and 100 mM Ca2+ over 8 weeks, which was then desorbed in the presence of Prussian blue (PB) nanoparticles over 12 weeks. The PB nanoparticles were used to inhibit the re-sorption of desorbed Cs+. More than 90% of Cs+ was sorbed to the minerals in the presence of Ca2+; meanwhile, only 50–70% of Cs+ was in the presence of K+. For all samples other than the illite with Ca2+ (Ca-illite), more than 80% of Cs+ were desorbed within a few days, and almost all Cs+ was desorbed at the end of the experiment. The large and fast desorption of Cs+ indicated a large part of Cs+ sorbed to these minerals were indeed labile in the presence of a strong sorbent like PB nanoparticles. These desorption trends were hardly influenced by a change of the sorption time. The desorption of Cs+ from the Ca-illite was slow, taking more than one month before 80% desorption for the sample with 1-day sorption, and the desorption amount only reached less than 90%. This slow desorption of Cs+ from the Ca-illite became even slower with the sorption time from one day to two weeks, and only 70% of sorbed Cs+ was desorbed at the end of the experiment for the latter. The mechanisms of Cs+ desorption from the Ca-illite was quantitatively explained by fitting to a pseudo first-order desorption model, suggesting that 30–40% of Cs+ was sorbed to the peripheral region of the interlayer of the Ca-illite and diffused into the interior part. The rest of sorbed Cs+ can be desorbed relatively fast. As this Cs+ was most likely sorbed to frayed edge sites in the Ca-illite, these results suggested that a part of the sorbed Cs+ (70 - 60%) was labile. Thus, the expansion and collapse of the peripheral regions of the interlayers induced by co-existing cations and interlayer migration of Cs+ are important processes constraining the sorption and desorption of Cs+ to/from the micaceous minerals. In addition, compared with the desorption from the pure minerals examined in this study, the desorption of Cs+ from real soils was slower likely due to weathering and/or the formation of aggregates.

International audience; Traces of Pu have been detected in material released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March of 2011; however, to date the physical and chemical form of the Pu have remained unknown. Here we report the discovery of particulate Pu associated with cesium-rich microparticles (CsMPs) that formed in and were released from the reactors during the FDNPP meltdowns. The Cs-pollucite-based CsMP contained discrete U(IV)O2 nanoparticles

Sorbed Cs on vermiculitized biotite in saturation amount was desorbed by extractions with 1M K+ and Mg2+ at varied temperatures. At room temperature, Cs+ was readily desorbed by leaching with K+ (~100%) but not by Mg2+ (~50%). However, contrary was true for desorption at high temperature, in which Mg2+ desorbed far more Cs+ (~100%) than that by K+ (~25%). XRD analysis of Cs depleted samples suggested that the contrary abilities of K+ and Mg2+ for Cs desorption at low and high temperatures were attributed to their induced interlayer collapse or expansion during extraction.

We demonstrate the improvement of phosphorus emitter passivation for an industrial-sized passivated emitter and rear cell (PERC) with selective emitter (SE) structure using a method of nitric acid oxidation of silicon (NAOS) to form ultrathin SiO 2 layer. The results clearly show a significant impact of the presence of NAOS-SiO 2 above emitters on all I-V parameters of PERCsWe observed an increase in the opencircuit voltage (V oc ), and theshort-circuit current density(J sc ) along with strong improvements in the internal quantum efficiency (IQE) for short-wavelength photons. These improvements can be ascribed to the high level of chemical passivation, as clearly shown by a reduced interface trap density (D it ), and it is due to the less Shockley-Read-Hall recombination. The results presented here suggest that NAOS surface pretreatment is a very promising technology to improve the level of chemical passivation and thereby enhancing the industrialsized PERC performance.

To understand the competing effects of the components in extracellular substances (ES), polymeric substances (PS) and low-molecular-weight small substances (SS) S. cerevisiae. The polypeptides and phosphates in all components preferentially adsorbed onto the CeNPs. The zeta potentials of ES + CeNPs, PS + CeNPs, and SS + CeNPs overlapped on the plot of PS itself, indicating the surface charge of the polymeric substances controls the zeta potentials. The sizes of the CeNP aggregates, 100–1300 nm, were constrained by the zeta potentials. The steric barrier derived from the polymers, even in SS, enhanced the CeNP dispersibility at pH 1.5–10. Consequently, the PS and SS had similar effects on modifying the CeNP surfaces. The adsorption of ES, which contains PS + SS, can suppress the aggregation of CeNPs over a wider pH range than that for PS only. The present study addresses the non-negligible effects of small-sized molecules derived from microbial activity on the migration of CeNP in aquatic environments, especially where bacterial consortia prevail.

This paper presents a study on the influence of the refractive index, n, of silicon nitride (SiNy) rear passivation films on the performance of passivated emitter and rear cells (PERCs). Symmetrical sample structures were fabricated in order to further investigate the associated electrical and interfacial properties. When the refractive index of the SiNy films, n, which can be varied by controlling the concentrations of silicon, hydrogen, and nitrogen, increases up to n = 2.3, the implied open-circuit voltage (iVoc) decreases significantly by 20 mV compared to that of the samples with refractive indexes n 2.3 is attributed to poor field-effect passivation and chemical passivation. For field-effect passivation, the effect is observed clearly through the reduction of the negative fixed charge density (Qf) near the interface due to the high silicon content in the films; here, a silicon atom back-bonded to three nitrogen atoms, known as the so-called K-centers, can be positively charged, thereby reducing Qf. For chemical passivation, an increase in the interface trap density (Dit) and increasing effective surface recombination velocity (Seff, max) are observed. These results suggest that controlling the conditions of SiNy deposition is crucial for assisting the surface passivation process that determines the final output of PERCs.