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Abstract: Hydrogen content and its distribution in in-core materials of nuclear plants are known to have a strong influence on their behaviour, especially on their mechanical properties but also on their corrosion resistance. This point has to be largely investigated in the case of the nuclear fuel cladding (Zr based alloys) of pressurized water reactors (PWR). Two situations have been considered here, with regards to the hydrogen content and its spatial distribution within the thickness of the tubes: [(1)] Irradiated fuel cladding tubes after a nominal period under working conditions in a PWR core. [(2)] Non-irradiated fuel cladding previously exposed to conditions representative of an hypothetical “loss of coolant accident” scenario (LOCA). As far as micrometric distributions of H were required, μ-ERDA has been performed at the nuclear microprobe of the Pierre Süe Laboratory. This facility is fitted with two beam lines. In the first one, used for non-active sample analysis, the μ-ERDA configuration has been improved to reduce the limits of detection and the reliability of the results. The second one offers the unique feature of being dedicated to radioactive samples. We will present the nuclear microprobe and emphasize on the μ-ERDA configuration of the two beam lines. We will illustrate the performance of the setup by describing the results obtained for Zircaloy-4 cladding both on non-irradiated and irradiated samples. [Copyright &y& Elsevier]

• Different precipitation behaviors were identified between three stainless steel grades using X-ray transmission synchrotron diffraction. • The specimens were heavily carburized in grains and at grain boundaries. • However, equilibrium of precipitation was not reached. • The blocking effect of carbides had to be considered and was observed to evolve with time and microstructure. • Precipitation at grain boundaries could not be simulated with the used model. Three steels were exposed in carburizing sodium at 600 and 650 °C. The kinetics and extent of carburization were characterized. Numerical simulations using the coupled thermodynamic-kinetic modeling software DICTRA were performed. It was proposed that the observed carbon diffusion profiles were induced by the combined diffusion of carbon in the grains and at grain boundaries coupled with the slow formation of carbides. The blocking effect of carbides on the carbon diffusion was observed to evolve as a function of time and microstructure. Acceptable agreement between experimental and simulated intragranular carbon profiles was achieved by optimizing the labyrinth factor and phases. [ABSTRACT FROM AUTHOR]

The aluminum alloy AlFeNi used as fuel cladding for the Jules Horowitz Reactor (JHR) may undergo corrosion in the reactor environment. In order to qualify the corrosion behavior of the fuel elements of the JHR in accidental conditions, several specimens of AlFeNi have been corroded at 250 °C for different durations (9–34 days) in distilled water at various pH (4.9, 5.2 and 5.6) chosen to simulate that currently considered for the JHR. On all specimens, the only crystalline corrosion product formed is boehmite (AlOOH). The corrosion film is composed of three oxide layers which show through thickness chemical composition variations. The iron–nickel precipitates pre-existing in the metal matrix are present in the inner and intermediate oxide layers though oxidized. For long corrosion times, some of the iron and nickel particles are released in the water and some precipitation is observed at the surface of the oxide layer. The effect of surface finish (as received or polished) and thermal treatment (annealed and not annealed) on the oxide growth rate has also been investigated. For durations over 25 days, pH = 5.6 appears to be more favorable than pH = 5.2 and 4.9 in terms of oxide thickness and weight gain limitation. This effect of pH is however reduced on unpolished specimens. The effect of surface finish on the corrosion behavior as measured by optical microscopy appears to be strong, especially for pH = 4.9 where polished samples exhibited an accelerated evolution of the oxide thickness and of the mass gain. This could be due to the combined effect of a strong acid solution (pH = 4.9) and of the local microstructural changes formed at the interface through polishing. The effect of thermal treatment on the behavior of unpolished AlFeNi specimens during corrosion tests in the conditions investigated was found to be small. In this study, microstructural and chemical analyses were performed on the corroded specimens in order to get a better understanding of the corrosion kinetics. The crystallographic nature of the boehmite layers investigated by X-ray diffraction is unaffected by the pH of the solution. Iron precipitates were identified on the oxide surface beyond 34 days of corrosion by Environmental Scanning Electron Microscope (ESEM). Finally, Electron Probe Micro-Analysis (EPMA) was used to determine the chemical composition of the metal matrix and of the different oxide layers and precipitates versus the pH of the solution. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened steels are new generation alloys that are usually processed by hot isostatic pressing (HIP). In this study, spark plasma sintering (SPS) was studied as an alternative consolidation technique. The influence of the processing parameters on the microstructure was quantified. The homogeneity of the SPSed materials was characterised by electron microprobe and microhardness. A combination of limited grain growth and minimised porosity can be achieved on semi-industrial compact. Excellent tensile properties were obtained compared to the literature. [ABSTRACT FROM AUTHOR]

The effects of the thermal ageing at 400°C, 500°C and 600°C during 5000h on the mechanical properties of a 18%Cr ODS ferritic steel are investigated. A hardening effect is observed after ageing at 400°C and 500°C, probably due to the presence of chromium rich α′ particles as suggested by the literature. The impact resistance and the ductility of the material are strongly lowered by the ageing at 600°C. This embrittlement is characterized on the fracture surfaces by the presence of cleavage facets on the whole range of testing temperatures. The intermetallic σ phase is found to be responsible for the occurrence of cleavage fracture on the material aged at 600°C, and thus for the significant embrittlement of this material. M23C6 carbides are also observed before and after thermal ageing. The lattice parameters of the σ phase and the M23C6 carbides observed in this 18%Cr ODS steel aged at 600°C during 5000h are measured. [ABSTRACT FROM AUTHOR]

Abstract: Oxide Dispersion Strengthened (ODS) steels are promising candidate materials for fission and fusion applications thanks to their improved properties related to both their fine grained microstructure and high density of Y–Ti–O nanoscale clusters (NCs). The Fe–14Cr–1W–0.3Ti–0.3Y2O3 ODS ferritic steel was produced by powder metallurgy: Iron-base gas atomized powders were mechanically alloyed with 0.3% Y2O3 particles in an attritor. Then, the ODS powders were encapsulated in a soft steel can, consolidated by hot extrusion and cold rolled under the shape of tube cladding. The present work investigates the evolution of the chemical composition and the microstructure after each stage of the fabrication route (i.e. mechanical alloying, extrusion and cold rolling). Chemical analysis indicates a significant increase of the carbon content and a moderate increase of oxygen and nitrogen after mechanical alloying compared to initial atomized powders. After extrusion, the measured oxygen content corresponds mainly to the oxygen coming from yttria addition during MA process. In addition, electron microprobe analyses are performed after hot extrusion to determine the concentration and the distribution of the constitutive elements (Cr, Ti, W, Y, O). The microstructure was investigated by transmission electron microscopy (TEM) and small angle neutron scattering (SANS) in order to characterize the size distribution of Y–Ti–O particles. TEM results reveal a fine microstructure (average grain size of 600nm in the transverse direction) including Y–Ti–O NCs with a mean diameter close to 3nm after extrusion. A slight coarsening of Y–Ti–O NCs is evidenced by SANS after cold rolling and heat treatments. [Copyright &y& Elsevier]

Abstract: This paper deals with the study of oxidation kinetics and the identification of oxygen diffusion coefficients of low-tin Zy-4 alloy at intermediate (973K⩽ T ⩽1123K) and high temperatures (T ⩾1373K). Two different cases were considered: dissolution of a pre-existing oxide layer in the temperature range 973K⩽ T ⩽1123K and oxidation at T ⩾1373K. The results are the following ones: in the temperature range 973–1123K, the oxygen diffusion coefficient in α Zr phase can be expressed as D α =6.798 exp(−217.99kJ/RT)cm2/s. In the temperature range 1373–1523K, the oxygen diffusion coefficients in α Zr, β Zr and ZrO2, were determined using an ‘inverse identification method’ from experimental high temperature oxidation data (i.e., ZrO2, and α Zr(O) layer thickness measurements); they can be expressed as follows: D α =1.543 exp(−201.55kJ/ RT) cm2/s, D β =0.0068 exp(−102.62kJ/ RT) cm2/s and . Finally an oxygen diffusion coefficient in α Zr in the temperature range 973K⩽ T ⩽1523K was determined, by combining the whole set of results: D α =4.604exp(−214.44kJ/RT)cm2/s. In order to check these calculated diffusion coefficients, oxygen concentration profiles were determined by Electron Probe MicroAnalysis (EPMA) in pre-oxidized low-tin Zy4 alloys annealed under vacuum at three different temperatures 973, 1073 and 1123K for different times, and compared to the calculated profiles. At last, in the framework of this study, it appeared also necessary to reassess the Zr–O binary phase diagram in order to take into account the existence of a composition range in the two zirconia phases, and . [Copyright &y& Elsevier]

Abstract: Coastal and estuarine systems are among the most threatened by human activities which damage their ecological function and, in particular, their nursery role for many marine species. In this context, the protection of these vital ecosystems is a critical issue for the management of fisheries resources. To that aim, functional approaches have to be developed that make it possible to assess habitat suitability and quality. The common sole, Solea solea (L.) was selected as an indicator species to identify the features of coastal and estuarine nursery habitats in the Bay of Biscay (France). Previous studies have shown that young-of-the-year (YOY) sole are strongly dependent upon various abiotic factors, and especially bathymetry, sediment cover and the extent of river plumes. We investigated whether taking into account biological variables, based on benthic macrofauna biomasses aggregated into trophic group, may improve the description of the juvenile sole distribution in the Vilaine estuary nursery. Results from Generalised Linear Models demonstrated the importance of integrating these biological variables in the determination of juvenile habitats at a local scale. The abundance of YOY sole was correlated with an index of the benthic invertebrates biomass and, more specifically, with the biomass of suspension feeders. This result was reinforced by a one-dimensional spatial statistical analysis, which pointed out the similar distribution of invertebrate macrobenthos and juvenile sole along the upstream/downstream gradient of the estuary. Moreover, the inter-annual variations of abundance and distribution of juveniles were synchronous with those of the macrobenthos. [Copyright &y& Elsevier]

Abstract: During the last fifteen years, CEA has acquired much experience in the control of the microstructure and the mechanical properties of ODS alloys for nuclear applications. Each major step of the production process has been studied to get the best compromise for the fabrication route of ODS materials. From this scientific background, two new Fe–13/18CrWTi ferritic ODS alloys have been designed to meet the needs of the fusion or GEN-IV programs. These new materials have been investigated at a semi- industrial scale with different industrial partners and consolidated as small plates. The aim of this paper is to present the recent CEA developments on ODS materials, and to show the first results obtained on the Fe–18Cr1WTi new ferritic ODS alloy. The fabrication route for these new materials is presented, along with the measured mechanical properties and the preliminary microstructure characterizations. These new materials look promising for nuclear applications and are considered by CEA as reference materials for the development of new ODS alloys. [Copyright &y& Elsevier]

In-situ time-resolved Synchrotron X-ray diffraction analyses were performed on zirconium alloy (Zircaloy-4) sheet samples, during their heating, isothermal oxidation at 700, 800 and 900 °C under a flowing mixture of He and O 2 and cooling. The oxide growth and the evolution of the oxide structure as a function of time and temperature were studied with suitable time resolution. Oxide layer thicknesses of approximately 10 μm were formed during the experiments. The incident X-rays penetrated the whole oxide thickness. The samples were examined after the experiments by field emission gun scanning electron microscopy, electron backscatter diffraction and electron-probe microanalysis. The results showed that the oxide contains a mixture of monoclinic and tetragonal zirconia evolving during heating, oxidation and cooling. The average volume fraction of tetragonal zirconia decreases during oxidation. This fraction is larger at 900 °C than at 700 and 800 °C. For oxide layers thinner than approximately 5 μm, this fraction is larger at 800 °C than at 700 °C, but it is rather equivalent for both temperatures when the oxide thickness ranges between 5 and 8 μm. Some of the tetragonal zirconia crystals transforms into the monoclinic phase during cooling after oxidation. This fraction of transformed tetragonal zirconia is larger after oxidation at 900 °C than after oxidation at 700 and 800 °C. It is suggested that these evolutions of the oxide crystallographic structure are related to micro-stresses and to temperature dependences of the critical size of zirconia crystals below which tetragonal zirconia is stabilized. [ABSTRACT FROM AUTHOR]