Thermomechanical fatigue of stainless steels for automotive exhaust systems

National audienceStainless steel grades are now widely used for automotive exhaust systems, in order to increase their durability. Indeed, the exhaust systems are subjected to ever more severe conditions and they include high technology components such as manifolds, catalytic converters and particle filters. This evolution is a direct consequence of the worldwide effort to decrease automotive pollutant emissions in accordance with the new environmental regulations. This paper deals with the thermomechanical fatigue (TMF) of stainless steels at high temperature, specially behaviour and damage models, and with the recent progress in the development TMF fatigue design tools using FEA related to the design of stainless steel exhaust manifolds. A numerical method is proposed for the design and the lifetime prediction of stainless steel exhaust manifold under a thermal fatigue load. It includes the modeling of manifolds submitted to the thermal cycle reproduced from motor bench tests. The identification of the constitutive law, in particular the elasto-viscoplastic model, for a wide range of temperatures, provides the most realistic stress-strain response of the structure. Finally, a dedicated damage criterion is proposed on the basis of the maximal temperature and plastic strain amplitude reached during a thermal cycle (modified-Taira model). Identification of a more general damage model on the basis of TMF tests is also discussed

Novel Insights into the Bovine Polled Phenotype and Horn Ontogenesis in Bovidae

Despite massive research efforts, the molecular etiology of bovine polledness and the developmental pathways involved in horn ontogenesis are still poorly understood. In a recent article, we provided evidence for the existence of at least two different alleles at the Polled locus and identified candidate mutations for each of them. None of these mutations was located in known coding or regulatory regions, thus adding to the complexity of understanding the molecular basis of polledness. We confirm previous results here and exhaustively identify the causative mutation for the Celtic allele (PC) and four candidate mutations for the Friesian allele (PF). We describe a previously unreported eyelash-and-eyelid phenotype associated with regular polledness, and present unique histological and gene expression data on bovine horn bud differentiation in fetuses affected by three different horn defect syndromes, as well as in wild-type controls. We propose the ectopic expression of a lincRNA in PC/p horn buds as a probable cause of horn bud agenesis. In addition, we provide evidence for an involvement of OLIG2, FOXL2 and RXFP2 in horn bud differentiation, and draw a first link between bovine, ovine and caprine Polled loci. Our results represent a first and important step in understanding the genetic pathways and key process involved in horn bud differentiation in Bovidae

Investigation of fission product isomeric ratios and angular momenta of

During an experimental campaign performed at the LOHENGRIN recoil spectrometer of the Institut Laue-Langevin (ILL), a kinetic energy dependence of 132Sn fission product isomeric ratio (IR) has been measured by inducing thermal fission of 241Pu. The IRs are deduced using gamma ray spectrometry in coincidence with the ionisation chamber. To interpret these data, we use the FIFRELIN Monte-Carlo code to simulate the de-excitation of the fission fragments. Combining the IRs with the FIFRELIN calculations, the angular momentum distribution with kinetic energy of the doubly magic nucleus of 132Sn was deduced. This will be compared with the angular momentum distribution obtained for the reaction 235U(nth,f) for 132Sn

Investigation of fission product isomeric ratios and angular momenta of 132^{132}Sn populated in the 241^{241}Pu(nth_{th},f) reaction

International audienceDuring an experimental campaign performed at the LOHENGRIN recoil spectrometer of the Institut Laue-Langevin (ILL), a kinetic energy dependence of 132Sn fission product isomeric ratio (IR) has been measured by inducing thermal fission of 241Pu. The IRs are deduced using gamma ray spectrometry in coincidence with the ionisation chamber. To interpret these data, we use the FIFRELIN Monte-Carlo code to simulate the de-excitation of the fission fragments. Combining the IRs with the FIFRELIN calculations, the angular momentum distribution with kinetic energy of the doubly magic nucleus of 132Sn was deduced. This will be compared with the angular momentum distribution obtained for the reaction 235U(nth,f) for 132Sn

Angular momentum of doubly magic ¹³²Sn fission product: Experimental and theoretical aspects

International audienceDespite the numerous theoretical and experimental works published very recently, the way in which fission fragments acquire their angular momentum is still an open question. This angular momentum generation mechanism is important not only for improving our understanding of the fission process, but also for nuclear energy applications, since the angular momentum of fission fragments strongly impact the prompt gamma spectra and consequently the decay heat in a reactor. In this context, within the framework of a collaboration between the ‘Laboratoire de Physique Subatomique et Corpusculaire’ (LPSC, France), the ‘Institut Laue Langevin’ (ILL, France) and the CEA-Cadarache (France), an experimental program was developed on the LO-HENGRIN mass-spectrometer with the aim of measuring isomeric ratio of some fission products for different thermal-neutron-induced fission reactions. This paper will be focused on the results obtained for the spherical nucleus 132Sn following thermal-neutron-induced fission of both 235U and 241Pu targets. To further challenge the angular momentum generation models, 132Sn isomeric ratio (IR) was measured as a function of 132Sn fission product kinetic energy (KE). The angular momentum was determined by combining our experimental data with the calculations performed with the FIFRELIN Monte Carlo code. A clear angular momentum decrease with KE was observed for both reactions. Lastly, we investigate the dependence of the 132Sn angular momentum with the incident neutron energy, from thermal region up to 5 MeV (below the second-chance fission). For that, the four free available parameters in FIFRELIN are selected in order to reproduce the average prompt neutron multiplicity. In this way, the angular momentum is deduced for each neutron energy. These results are discussed in terms of the impact of the available intrinsic excitation energy at scission on the spin generation mechanism.</jats:p

Development of a gas filled magnet spectrometer coupled with the Lohengrin spectrometer for fission studies

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Electromagnetic isotope separation of gadolinium isotopes for the production of 152,155Tb for radiopharmaceutical applications

International audienceA demo experiment was performed at the tandem accelerator of MLL Garching where 152Tb was produced by irradiating a unique ion-implanted 152Gd target (99% enriched) with 8 and 12 MeV protons respectively. At these energies mainly 152Tb was produced by (p,n) reactions plus a small quantity of 153Tb by (p,g) reactions. Upper limits are derived for co-production of other Tb isotopes. The achieved radionuclidic purity would enable direct use for human applications. Gd isotopes of adequate isotopic enrichment could be separated with the SIDONIE mass separator at CSNSM Orsay and prepared as cyclotron targets suited for high current irradiations. In a demo experiment samples of highly enriched 158Gd were produced at SIDONIE. The sample purity was characterized by prompt gamma activation analysis at NPI Řež. The neighboring mass 157Gd was found to be suppressed by three to five orders of magnitude, depending on the sample position in the SIDONIE separator

New measurements on isobaric fission product yields and mean kinetic energy for 241Pu thermal neutron-induced fission

Nuclear fission yields data measurements for thermal neutron induced fission of 241Pu have been carried out at the Institut Laue Langevin (ILL) in Grenoble, using the Lohengrin mass spectrometer. Mass, isotopic and isomeric yields have been extracted for the last measurements. A focus is given in this document to the mass yield results which are obtained for almost the entire heavy peak and most of the light high yields masses, along with the covariance matrix. The mean kinetic energy as a function of the fission product mass has also been extracted from the measurements. The total mean kinetic energy pre and post neutron emission have been assessed and compared to other works showing a rather good agreement

New measurements on isobaric fission product yields and mean kinetic energy for

Nuclear fission yields data measurements for thermal neutron induced fission of 241Pu have been carried out at the Institut Laue Langevin (ILL) in Grenoble, using the Lohengrin mass spectrometer. Mass, isotopic and isomeric yields have been extracted for the last measurements. A focus is given in this document to the mass yield results which are obtained for almost the entire heavy peak and most of the light high yields masses, along with the covariance matrix. The mean kinetic energy as a function of the fission product mass has also been extracted from the measurements. The total mean kinetic energy pre and post neutron emission have been assessed and compared to other works showing a rather good agreement