Cold spray Cr-coated Optimized ZIRLO claddings: an option for accident tolerant fuels

Accident tolerant fuel development has started with the aim of providing nuclear fuels able to endure severe accident conditions. Research in this field has also sparked a wave of material renewal in the nuclear industry that had being delayed for the last few decades. Climate change is an ever-growing public concern, and policies about greenhouse gas emissions are becoming more stringent both at the national and international level. Nuclear energy produces very low carbon emissions and the successful development of new accident tolerant materials might play a role in making this technology a viable solution to this global issue. Cr-coated zirconium claddings are one of the most promising candidates as near-term response to the need for accident tolerant materials. These coatings can be produced via a range of different technologies, but the two main designs being currently developed are obtained with physical vapour deposition or cold spray (CS) deposition. In cold spray, high pressure gas is fed through a nozzle together with Cr powder. The Cr particles are accelerated up to 1200 m/s and directed to the substrate, in this case cladding tubes made of Optimized ZIRLO™ alloy. The resulting Cr-coated zirconium cladding is the subject of this work. As-fabricated samples and autoclave tested material are characterized with atom probe tomography and a range of electron microscopy techniques. The scope of the investigation is to evaluate the performances of Cr-coated claddings under operating conditions. Additionally, the nature of the adhesion in cold spray coating and the effects of this deposition method on the substrate are explored. A 10-20 nm thick intermixed bonding region was observed at the Cr/Zr interface of the as-fabricated cladding. This region is deemed to play an important role in the strong adhesion of CS coatings. When exposed to operating conditions, ZrCr2-Laves phase was found to nucleate in the intermixed bonding region. CS deposition involves severe plastic deformation of both coating and substrate. As a result, a 1-2 μm thick nanocrystalline layer can be found in the substrate adjacent to the Cr/Zr interface. After autoclave exposure, a Zr-Cr-Fe phase was discovered precipitating in this nanocrystalline layer at the Zr grain boundaries

Development and performance evaluation of accident-tolerant coated fuel claddings for light water reactors

The development of accident tolerant fuel has the aim of providing nuclear fuels able to endure severe accident conditions. Research in this field has also sparked a wave of material renewal in the nuclear industry that had been delayed for the last few decades. Climate change is an ever-growing public concern, and policies about greenhouse gas emissions are becoming more stringent both at the national and international level. Nuclear energy produces very low carbon emissions and the successful development of new accident tolerant materials might play a role in making this technology a viable solution to this global issue. Coated zirconium claddings are one of the most promising candidates as a near-term response to the need for accident tolerant materials. These coatings can be produced via a range of different technologies, but two main techniques are being currently employed for the development of such coatings: cold spray deposition and physical vapour deposition (PVD). In cold spray, high pressure gas is fed through a nozzle together with a powder. Powder particles are accelerated up to 1200 m/s and directed to the substrate, in this case cladding tubes made of zirconium alloy. In PVD, the coating material is evaporated from a target and sputtered onto the substrate as atoms or ions. The resulting coated zirconium claddings are the subject of this work.As-fabricated samples, autoclave tested material, and specimens tested under simulated accident conditions are characterized with atom probe tomography and a range of electron microscopy techniques. The scope of the investigation is to evaluate the performance of the coated claddings under operating conditions and in simulated accident conditions. Metallic Cr has emerged as the best candidate for accident tolerant coatings for pressurised water reactors. In this work, the focus was on Cr-coatings deposited with cold spray, which performed well in both tested environments. A passivating layer of chromia formed during autoclave exposure, and a protective scale of chromia prevented any oxidation of the Zrsubstrate for up to 40 min in 1200  C steam. The nature of the adhesion in cold spray coatings and the effects of this deposition method on the substrate were studied. The formation of a Cr2Zr phase at the Cr/Zr interface was observed both under autoclave and simulated accident conditions. The search for an effective accident tolerant coating for boiling water reactors is more challenging and many coatings have been tested in autoclave, where PVD (Cr,Nb)N coatings showed the best performance under operating conditions. A 200 nm thick passivating oxide film composed of an outer Cr, Nb, Ni phase and an inner layer of oxidised coating was found after exposure

Not only P-glycoprotein: amplification of the ABCB1-containing chromosome region 7q21 confers multidrug resistance upon cancer cells by coordinated overexpression of an assortment of resistance-related proteins

The development of drug resistance continues to be a dominant hindrance toward curative cancer treatment. Overexpression of a wide-spectrum of ATP-dependent efflux pumps, and in particular of ABCB1 (P-glycoprotein or MDR1) is a well-known resistance mechanism for a plethora of cancer chemotherapeutics including for example taxenes, anthracyclines, Vinca alkaloids, and epipodopyllotoxins, demonstrated by a large array of published papers, both in tumor cell lines and in a variety of tumors, including various solid tumors and hematological malignancies. Upon repeated or even single dose treatment of cultured tumor cells or tumors in vivo with anti-tumor agents such as paclitaxel and doxorubicin, increased ABCB1 copy number has been demonstrated, resulting from chromosomal amplification events at 7q11.2-21 locus, leading to marked P-glycoprotein overexpression, and multidrug resistance (MDR). Clearly however, additional mechanisms such as single nucleotide polymorphisms (SNPs) and epigenetic modifications have shown a role in the overexpression of ABCB1 and of other MDR efflux pumps. However, notwithstanding the design of 4 generations of ABCB1 inhibitors and the wealth of information on the biochemistry and substrate specificity of ABC transporters, translation of this vast knowledge from the bench to the bedside has proven to be unexpectedly difficult. Many studies show that upon repeated treatment schedules of cell cultures or tumors with taxenes and anthracyclines as well as other chemotherapeutic drugs, amplification, and/or overexpression of a series of genes genomically surrounding the ABCB1 locus, is observed. Consequently, altered levels of other proteins may contribute to the establishment of the MDR phenotype, and lead to poor clinical outcome. Thus, the genes contained in this ABCB1 amplicon including ABCB4, SRI, DBF4, TMEM243, and RUNDC3B are overexpressed in many cancers, and especially in MDR tumors, while TP53TG1 and DMTF1 are bona fide tumor suppressors. This review describes the role of these genes in cancer and especially in the acquisition of MDR, elucidates possible connections in transcriptional regulation (co-amplification/repression) of genes belonging to the same ABCB1 amplicon region, and delineates their novel emerging contributions to tumor biology and possible strategies to overcome cancer MDR

Cold sprayed Cr-coating on Optimized ZIRLO™ claddings: the Cr/Zr interface and its microstructural and chemical evolution after autoclave corrosion testing

Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray deposition process is studied. Microstructure and chemistry of this material are investigated before and after exposure to autoclave corrosion testing with scanning electron microscopy, energy dispersive spectroscopy analysis, electron backscattered diffraction, transmission electron microscopy and atom probe tomography. The results are used to assess what changes have occurred upon autoclave exposure. The formation of a compact, 80 – 100 nm thick Cr2O3 layer is observed on the surface of the exposed samples. Nucleation of ZrCr2 intermetallic phase is discovered at the Cr/Zr interface. This Laves phase nucleates inside the intermixed bonding layer that can be found in both pristine and exposed samples, and decorates the interface in the form of small particles (less than 50 nm in size). Using transmission electron microscopy and atom probe tomography the growth of a Zr-Cr-Fe phase was detected. This phase is found in the region of the Zr-substrate immediately adjacent to the coating, up to a few hundred nanometres distance from the Cr/Zr interface. A small degree of recrystallization occurs upon autoclave exposure in the 1-2 \ub5m thick nanocrystalline layer produced on the Zr-substrate by the cold spray deposition method utilized for the fabrication of the Cr-coating

Stream hydrological fragmentation drives bacterioplankton community composition

In Mediterranean intermittent streams, the hydrological fragmentation in summer and the successive water flow reconvergence in autumn allow exploring how local processes shape the microbial community within the same habitat. The objectives of this study were to determine how bacterial community composition responded to hydrological fragmentation in summer, and to evaluate whether the seasonal shifts in community composition predominate over the effects of episodic habitat fragmentation. The bacterial community was assessed along the intermittent stream Fuirosos (Spain), at different levels of phylogenetic resolution by in situ hybridization, fingerprinting, and 16S rRNA gene sequencing. The hydrological fragmentation of the stream network strongly altered the biogeochemical conditions with the depletion of oxidized solutes and caused changes in dissolved organic carbon characteristics. In the isolated ponds, beta-Proteobacteria and Actinobacteria increased their abundance with a gradual reduction of the alpha-diversity as pond isolation time increased. Moreover, fingerprinting analysis clearly showed a shift in community composition between summer and autumn. In the context of a seasonal shift, the temporary stream fragmentation simultaneously reduced the microbial dispersion and affected local environmental conditions (shift in redox regime and quality of the dissolved organic matter) tightly shaping the bacterioplankton community composition

Expression of ID4 protein in breast cancer cells induces reprogramming of tumour-associated macrophages

Background: As crucial regulators of the immune response against pathogens, macrophages have been extensively shown also to be important players in several diseases, including cancer. Specifically, breast cancer macrophages tightly control the angiogenic switch and progression to malignancy. ID4, a member of the ID (inhibitors of differentiation) family of proteins, is associated with a stem-like phenotype and poor prognosis in basal-like breast cancer. Moreover, ID4 favours angiogenesis by enhancing the expression of pro-angiogenic cytokines interleukin-8, CXCL1 and vascular endothelial growth factor. In the present study, we investigated whether ID4 protein exerts its pro-angiogenic function while also modulating the activity of tumour-associated macrophages in breast cancer. Methods: We performed IHC analysis of ID4 protein and macrophage marker CD68 in a triple-negative breast cancer series. Next, we used cell migration assays to evaluate the effect of ID4 expression modulation in breast cancer cells on the motility of co-cultured macrophages. The analysis of breast cancer gene expression data repositories allowed us to evaluate the ability of ID4 to predict survival in subsets of tumours showing high or low macrophage infiltration. By culturing macrophages in conditioned media obtained from breast cancer cells in which ID4 expression was modulated by overexpression or depletion, we identified changes in the expression of ID4-dependent angiogenesis-related transcripts and microRNAs (miRNAs, miRs) in macrophages by RT-qPCR. Results: We determined that ID4 and macrophage marker CD68 protein expression were significantly associated in a series of triple-negative breast tumours. Interestingly, ID4 messenger RNA (mRNA) levels robustly predicted survival, specifically in the subset of tumours showing high macrophage infiltration. In vitro and in vivo migration assays demonstrated that expression of ID4 in breast cancer cells stimulates macrophage motility. At the molecular level, ID4 protein expression in breast cancer cells controls, through paracrine signalling, the activation of an angiogenic programme in macrophages. This programme includes both the increase of angiogenesis-related mRNAs and the decrease of members of the anti-angiogenic miR-15b/107 group. Intriguingly, these miRNAs control the expression of the cytokine granulin, whose enhanced expression in macrophages confers increased angiogenic potential. Conclusions: These results uncover a key role for ID4 in dictating the behaviour of tumour-associated macrophages in breast cancer

Multiple growth of graphene from a pre-dissolved carbon source

Mono- to few-layer graphene materials are successfully synthesized multiple times using Cu-Ni alloy as a catalyst after a single-chemical vapor deposition (CVD) process. The multiple synthesis is realized by extracting carbon source pre-dissolved in the catalyst substrate. Firstly, graphene is grown by the CVD method on Cu-Ni catalyst substrates. Secondly, the same Cu-Nicatalyst foils are annealed, in absence of any external carbon precursor, to grow graphene using the carbon atoms pre-dissolved in the catalyst during the CVD process. This annealing process is repeated to synthesize graphene successfully until carbon is exhausted in the Cu-Ni foils. After the CVD growth and each annealing growth process, the as-grown graphene is removed using a bubbling transfer method. A wide range of characterizations are performed to examine the quality of the obtained graphene material and to monitor the carbon concentration in the catalyst substrates. Results show that graphene from each annealing growth process possesses a similar quality, which confirmed the good reproducibility of the method. This technique brings great freedom to graphene growth and applications, and it could be also used for other 2D material synthesis

Comparing CrN and TiN Coatings for Accident-Tolerant Fuels in PWR and BWR Autoclaves

The development of coatings for accident-tolerant fuels (ATFs) for light water reactor (LWR) applications promises improved corrosion resistance under accident conditions and better performances during operation. CrN and TiN coatings are characterized by high wear resistance coupled with good corrosion resistance properties. They are generally used to protect materials in applications where extreme conditions are involved and represent promising candidates for ATF. Zr cladding tubes coated with 5 \ub5m-thick CrN or TiN, exposed in an autoclave to simulated PWR chemistry and BWR chemistry, were characterized with SEM, EDS, and STEM. The investigation focused on the performance and oxidation mechanisms of the coated claddings under simulated reactor chemistry. Both coatings provided improved oxidation resistance in a simulated PWR environment, where passivating films of Cr2O3\ua0and TiO2, less than 1 \ub5m-thick, formed on the CrN and TiN outer surfaces, respectively. Under the more challenging BWR conditions, any formed Cr2O3\ua0dissolved into the oxidizing water, resulting in the complete dissolution of the CrN coating. For the TiN coating, the formation of a stable TiO2\ua0film was observed under BWR conditions, but the developed oxide film was unable to stop the flux of oxygen to the substrate, causing the oxidation of the substrate

Quality and reactivity of dissolved organic matter in a Mediterranean river across hydrological and spatial gradients.

Understanding DOM transport and reactivity in rivers is essential to having a complete picture of the global carbon cycle. In this study, we explore the effects of hydrological variability and downstream transport on dissolved organic matter (DOM) dynamics in a Mediterranean river. We sampled the main stem of the river Tordera from the source to the sea, over a range of fifteen hydrological conditions including extreme events (flood and drought). By exploring spatial and temporal gradients of DOM fluorescence properties, river hydrology was found to be a significant predictor of DOM spatial heterogeneity. An additional space-resolved mass balance analysis performed on four contrasting hydrological conditions revealed that this was due to a shift in the biogeochemical function of the river. Flood conditions caused a conservative transport of DOM, generating a homogeneous, humic-like spatial profile of DOM quality. Lower flows induced a non-conservative, reactive transport of DOM, which enhanced the spatial heterogeneity of DOM properties. Moreover, the downstream evolution of DOM chemostatic behaviour revealed that the role of hydrology in regulating DOM properties increased gradually downstream, indicating an organised inter-dependency between the spatial and the temporal dimensions. Overall, our findings reveal that riverine DOM dynamics is in constant change owing to varying hydrological conditions, and emphasize that in order to fully understand the role of rivers in the global carbon cycle, it is necessary to take into account the full range of hydrological variability, from floods to droughts

CrN–NbN nanolayered coatings for enhanced accident tolerant fuels in BWR

The accident tolerant fuel (ATF) concept has emerged in the years after the 2011 Fukushima accident as part of a renewed effort in research for light water reactors. The primary focus is to further improve safety measures under and beyond design basis accident conditions, and to improve fuel cladding performance in normal operation. The application of a coating on zirconium claddings can achieve both these aims without extensive changes to the reactor design. Metallic chromium coatings have been profusely studied as solution for pressurized water reactors, but the search for an effective ATF coating able to withstand the environment inside boiling water reactors (BWRs) is still ongoing. In this work, two different versions of a novel nitride coating composition were studied. Zirconium claddings coated with 8 µm thick layers of superlattice CrN–NbN and a nanolayered CrN–NbN were tested in autoclave under BWR operating conditions for 60 days. Scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, electron back-scattered diffraction, x-ray diffraction, and atom probe tomography were employed to characterize as-deposited and autoclaved samples of these two materials. During exposure, both coating versions formed a stable, dense and passivating oxide scale (200–300 nm thick) on the surface, demonstrating improved oxidation protection under operating conditions. Some differences in the oxide growth mechanism were observed between the superlattice and the nanolayered CrN–NbN coatings, which allowed to glimpse at the effect of the layer thickness on the oxidation protection provided by these coatings. The nano-structured morphology of both coatings remained unaffected by the autoclave test, but a 35 nm thick Zr-Cr-N phase was found at the coating-substrate interface of the superlattice CrN–NbN coated cladding