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Inconel 625 is considered one of the candidate materials for fuel cladding in the Canadian supercritical water reactor. Gas tungsten arc welding (GTAW) is being evaluated as a joining technique for SCWR fuel cladding since this method is widely used to join components in the power and nuclear industry. The thermal cycle, during the GTAW process, produces different types of microstructures that affect the material's mechanical properties. The objective of this work was to study the effect of corrosion testing at supercritical water conditions on mechanical properties of Inconel 625 base material (BM) and weldments. Tubular Inconel 625 specimens were welded using a GTAW orbital process. Corrosion testing was conducted in an autoclave at 575 °C (848.15 K) and 23.5 MPa for 500 h (1.8 × 106 s). Weld characterization included mechanical tests, optical microscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. The composition of second phase precipitates observed during microstructural characterization was elucidated using equilibrium phase diagrams. Tensile tests showed that both BM and welds displayed an increase in strength and a decrease in ductility after corrosion testing. The ultimate tensile strength increased about 2% and 9% for the BM and the weldment, respectively. The maximum specimen elongation decreased around 35% for the BM and 45% for the weldment. The microstructure showed indications of second phase precipitation and grain morphology changes produced by both welding and corrosion processes. Results show that ductility of Inconel 625 GTAW welds is significantly reduced after exposure to supercritical water for 500 h (1.8 × 106 s).

Canadian Nuclear Laboratories has an on-going Research & Development program to support the development of a scaled–down 300 MWe version of the Canadian Super-Critical Water Reactor concept. The 300 MWe and 170–channel reactor core concept uses low enriched uranium fuel and features a maximum cladding temperature of 500 °C. Our goal is to test surface-modified zirconium alloys for use as fuel cladding. Zirconium alloys are attractive as they offer low neutron cross section thereby allowing the use of low enriched fuel. In this paper, we report on the results of general corrosion experiments used to evaluate chromium-coated zirconium-based alloys in the two chemistries (630 μg/kg O2 in both de-aerated and lithiated supercritical water). These experiments were conducted in a refreshed autoclave at 500 °C and 23.5 MPa. After exposure, the weight gain and the hydrogen absorption were examined. At adequate coating thickness, longitudinal and transverse coupons show similar corrosion behavior with improved corrosion resistance compared to uncoated coupons. The measured concentrations of hydrogen absorption are higher for the transverse coupons. Alkaline treatment resulted in higher weight gains than was found in pure oxygenated supercritical water.

Magnetite is a major corrosion product of carbon steel that forms deposits in the steam generators in water-cooled nuclear reactors. Sulfate is present as an impurity in the steam generator feed water and accumulates in the magnetite deposits, leading to formation of acidic crevices, corrosion and stress corrosion cracking of steam generator tubing. Reliable adsorption data are required to understand material degradation of steam generator tubing. Sulfate adsorption onto magnetite has been studied at temperatures from 25 to 300 °C as a function of pH, and chloride and sulfate concentrations. The results show that adsorption decreases with increasing pH and ionic strength, and adsorption followed the Langmuir adsorption isotherm. Overall, sulfate adsorption onto magnetite is endothermic and the enthalpy of adsorption depends on the pH and ionic strength of the solutions. The adsorption behavior of sulfate onto magnetite is explained through outer-sphere and inner-sphere adsorption.

The 300 MWel small Canadian supercritical water-cooled reactor (SCWR), which is a scaled-down version of the original 1200 MWel concept, has a smaller core, uses low enriched uranium fuel instead of a plutonium–thorium fuel, and features a lower (maximum) cladding temperature of 500 °C. The lower cladding temperature may permit the use of different alloys, including zirconium alloys, which had been ruled out as candidates for the Canadian SCWR, whose cladding temperature may reach 850 °C. The potential to use zirconium alloys is exciting because they have a low neutron cross section, which in turn means that fewer neutrons are lost, and the fuel can be used more efficiently. One advantage, for example,, is that the fuel cycle can be lengthened. In this paper, we report on the results of corrosion experiments used to screen zirconium- and titanium-based alloys as well as corrosion-resistant coating materials such as Cr and Al as potential candidates for fuel cladding in the small Canadian SCWR. These experiments were conducted in a refreshed autoclave in deaerated supercritical water at 500 °C and 23.5 MPa. After exposure, the weight gain was measured, and the oxide thickness and the oxide phases were examined. Of all materials, the coated and uncoated Ti-grade 2 and Ti-grade 5 alloys met our screening qualification criteria, however, Al/Cr-coated zirconium coupons showed notable improvement and will be explored further in future testing.

Radioactive cesium, strontium and europium can be released as fission products during nuclear incidents and pose a major concern to contamination control because of their biological activity and long decay half-lives. Experiments were performed to study the kinetics and equilibrium of the adsorption of inactive Cs(I), Sr(II) and Eu(III) ions on a natural sandy soil. It was found that the adsorption of Cs(I), Sr(II) and Eu(III) had a second order reaction kinetics and generally reached equilibrium within 7 days. The adsorption equilibria of Cs(I) follows a Freundlich isotherm, while those of Sr(II) and Eu(III) follows a Langmuir isotherm. Adsorption increases with increasing pH for these cations studied at temperatures from 25 to 50°C. In general, the temperature effect on cation adsorption is small under these test conditions suggesting that the enthalpy change for adsorption is not significant. Tests of mixed Cs(I) and Sr(II) adsorption suggested that these cations likely adsorb on different sites on the surface of sandy soil. The desorption tests in NaCl and CaCl2 solutions show that Eu(III) and Cs(I) are more tightly bound and less mobile in natural sandy soil than Sr(II) under the same test conditions. Tests of Cs(I), Sr(II) and Eu(III) in a column under a flowing condition revealed that these cations mainly adsorbed within the depth of 2 cm below the surface of sandy soil.

Most supercritical water-cooled reactor (SCWR) concepts being considered as part of the Generation IV initiative are direct cycle. In the event of a fuel defect, the coolant will contact the fuel pellet, potentially releasing fission products and actinides into the coolant and transporting them to the turbines. At the high pressure (25 MPa) in an SCWR, the coolant does not undergo a phase change as it passes through the critical temperature in the core, and nongaseous species may be transported out of the core and deposited on out-of-core components, leading to increased worker dose. It is therefore important to identify species with a high risk of release and develop models of their transport and deposition behavior. This paper presents the results of preliminary leaching tests in SCW of U-Th simulated fuel pellets prepared from natural U and Th containing representative concentrations of the (inactive) oxides of fission products corresponding to a fuel burnup of 60 GWd/ton. The results show that Sr and Ba are released at relatively high concentrations at 400°C and 500°C.

Further to the outstanding results of the first generation of Infrared Atmospheric Sounding Interferometer (IASI) instrument [1] in the fields of operational meteorology, air quality, atmospheric chemistry, and climate monitoring [2], the Centre National d'Etudes Spatiales (CNES), i.e. the French national space agency, decided in 2010 to develop the New Generation of the Infrared Atmospheric Sounding Interferometer (IASI-NG). With notable improvements on spectral and radiometric performances compared with the first generation, IASI-NG will be a CNES contribution to the EUMETSAT Polar System Second Generation (EPS-SG) program [3] which aims to provide continuity of observations for weather forecasting, atmospheric chemistry and climate change in the 2020 to 2040 timeframe. IASI-NG is a key element of the payload of the METOP-SG A series of European meteorological polar-orbiting satellites Second Generation [4]. The first flight model in this series is scheduled for launch by early 2020 decade. IASI-NG represents a significant technological and scientific step forward that will provide meteorologists with atmospheric emission spectra to derive temperature and humidity profiles. The instrument is designed to measure atmospheric spectra in the infrared. It is composed of a Fourier Transform Spectrometer (FTS) with a field compensation device and an associated imager. This paper will present the objectives and the outlines of the IASI-NG program with focus on CNES involvements in this cooperation for the development and operations of the IASI-NG instruments.

Nine neurodegenerative diseases including Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) are caused by an expansion of a polyglutamine (polyQ) stretch in the respective proteins. Aggregation of expanded polyQ-containing proteins into the nucleus is a hallmark of these diseases. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of these diseases. Using SCA7 and HD mouse models in which we recently described a retinal phenotype, we investigated whether altered gene expression underlies photoreceptor dysfunction. In both models, rhodopsin promoter activity was early and dramatically repressed, suggesting that downregulation of photoreceptor-specific genes plays a major role in polyQ-induced retinal dysfunction. Because the rhodopsin promoter drives mutant ataxin-7 expression in our SCA7 mice, we also assessed whether downregulation of mutantSCA7transgene would reverse retinopathy progression and aggregate formation. Although residual expression of mutant ataxin-7 was found negligible from 9 weeks of age, SCA7 transgenic mice showed a progressive decline of photoreceptor activity leading to a complete loss of electroretinographic responses from 1 year of age. At this age, aggregates were cleared in only half of the photoreceptors, indicating that their formation is not fully reversible in this model. We demonstrate here that abolishing full-length mutant ataxin-7 expression did not reverse retinopathy progression in SCA7 mice, raising the possibility that some polyQ-induced pathological events might be irreversible.