Toward Spin–Orbit Coupled Diabatic Potential Energy Surfaces for Methyl Iodide Using Effective Relativistic Coupling by Asymptotic Representation

The theoretical treatment of state–state interactions and the development of coupled multidimensional potential energy surfaces (PESs) is of fundamental importance for the theoretical investigation of nonadiabatic processes. Usually, only derivative or vibronic coupling is considered, but the presence of heavy atoms in a system can render spin–orbit (SO) coupling important as well. In the present study, we apply a new method recently developed by us (<i>J. Chem. Phys.</i> <b>2012</b>, <i>136</i>, 034103, and <i>J. Chem. Phys.</i> <b>2012</b>, <i>137</i>, 064101) to generate SO coupled diabatic PESs along the C–I dissociation coordinate for methyl iodide (CH₃I). This is the first and mandatory step toward the development of fully coupled full-dimensional PESs to describe the multistate photodynamics of this benchmark system. The method we use here is based on the diabatic asymptotic representation of the molecular fine structure states and an effective relativistic coupling operator. It therefore is called effective relativistic coupling by asymptotic representation (ERCAR). This approach allows the efficient and accurate generation of fully coupled PESs including derivative and SO coupling based on high-level <i>ab initio</i> calculations. In this study we develop a specific ERCAR model for CH₃I that so far accounts only for the C–I bond cleavage. Details of the diabatization and the accuracy of the results are investigated in comparison to reference <i>ab initio</i> calculations and experiments. The energies of the adiabatic fine structure states are reproduced in excellent agreement with <i>ab initio</i> SO–CI data. The model is also compared to available literature data, and its performance is evaluated critically. This shows that the new method is very promising for the construction of fully coupled full-dimensional PESs for CH₃I to be used in future quantum dynamics studies

Oxydation et protection des matériaux pour sous-couches (NiAlPd, NiAlPt, NiCoCrAlYTa, CoNiCrAlY) de barrières thermiques

Le comportement en oxydation isotherme des divers matériaux utilisés pour la fabrication des sous-couches pour barrières thermiques (systèmes superalliage base-nickel/sous-couche/zircone partiellement stabilisée) a été caractérisé en fonction de la température (900 à 1 100°C), de la vitesse de montée en température (12,20 ou 60 K/min) et de l'atmosphére (pressions partielles d'oxygène de 10-5, 1 ou 105 Pa). Cela nous a permis de définir les conditions de pré-oxydation permettant de contrôler l'oxyde formé sur la sous-couche avant le dépôt de la zircone. Pour les aluminiures de nickel modifiés palladium ou platine comme pour les sous-couches MCrAlY, une transition cinétique est observée lors d'oxydations courtes (6h) en dessous de 1000°C (entre 1000 et 1100°C pour (Ni,Pt)Al). L'analyse thermogravimétrique combinée aux analyses chimiques (XPS, SIMS, MEB-EDS) et structurales (DRX) montrent que cet accroissement des cinétiques d'oxydation à 900°C est dû à la formation d'alumine de transition ( θ ou δ). La transition peut être supprimée en combinant un état de surface sablé (aluminiures) ou rectifié (MCrAlY) et une oxydation sous vide primaire d'air (10 Pa)

CAST3M modelling of a spent fuel assembly bending during a handling accident Rod failure risk evaluation from the experimental results of spent fuel rod bending test

International audienceThe fuel handling operating rules exclude any accidental risk. However in the framework of the PRECCI R&D project, the bending of a spent fuel assembly resulting from its locking during a translation displacement is taken into account. This enabled us to develop an approach based on experiments and calculations that allows us to simulate the behaviour of an assembly under such loading. This study was carried out in CEA laboratories with the funding and the technical support of EDF. A three points bending test on a spent fuel rod segment was performed at the Laboratory for Mechanical Behaviour of Irradiated Materials (LCMI). From the experimental strength-displacement curve, a maximum failure strain, a maximum failure curvature and an equivalent constitutive equation were determined. CAST3M modelling of the fuel rod taking into account the elasto-plastic behaviour of the clad and the cracking of the UO2 fuel pellets was verified by the experimental results. Consequently, the identification of the respective contributions of the clad and of the pellets to the rod global behaviour was made possible. A two dimensional assembly with beam elements was modelled with CAST3M. The properties of the beams modelling the different parts of the assembly (top and bottom nozzle, grids) were chosen and adjusted according to their materials (zirconium alloys, steel) in order to obtain stiffness, tensile and shear behaviour, sliding and holding functions close to the experimental ones. Assembly bending calculations were performed. In order to obtain a rod integrity estimator, their maximum calculated strains and curvatures as a function of the bending angles can be compared to the failure experimental ones

CAST3M modelling of a spent fuel assembly bending during a handling accident Rod failure risk evaluation from the experimental results of spent fuel rod bending test

International audienceThe fuel handling operating rules exclude any accidental risk. However in the framework of the PRECCI R&D project, the bending of a spent fuel assembly resulting from its locking during a translation displacement is taken into account. This enabled us to develop an approach based on experiments and calculations that allows us to simulate the behaviour of an assembly under such loading. This study was carried out in CEA laboratories with the funding and the technical support of EDF. A three points bending test on a spent fuel rod segment was performed at the Laboratory for Mechanical Behaviour of Irradiated Materials (LCMI). From the experimental strength-displacement curve, a maximum failure strain, a maximum failure curvature and an equivalent constitutive equation were determined. CAST3M modelling of the fuel rod taking into account the elasto-plastic behaviour of the clad and the cracking of the UO2 fuel pellets was verified by the experimental results. Consequently, the identification of the respective contributions of the clad and of the pellets to the rod global behaviour was made possible. A two dimensional assembly with beam elements was modelled with CAST3M. The properties of the beams modelling the different parts of the assembly (top and bottom nozzle, grids) were chosen and adjusted according to their materials (zirconium alloys, steel) in order to obtain stiffness, tensile and shear behaviour, sliding and holding functions close to the experimental ones. Assembly bending calculations were performed. In order to obtain a rod integrity estimator, their maximum calculated strains and curvatures as a function of the bending angles can be compared to the failure experimental ones

Impact of irradiation damage recovery during transportation on the subsequent room temperature tensile behavior of irradiated zirconium alloys

16th International Symposium on Zirconium in the Nuclear Industry, 9th May 2010 – 13th May 2010, Chengdu, Sichuan Province, ChinaInternational audienceZirconium alloys are commonly used in Pressurized Water Reactor as fuel rod cladding tubes. After irradiation and cooling in pool, the Spent Nuclear Fuel Assemblies are either transported for wet storage to a devoted site or loaded in suitable casks for dry storage on Nuclear Power Plant site. During dry transportation or at the beginning of dry storage, at temperatures around 400°C, the cladding experiences a creep deformation under the hoop stress induced by the internal pressure of the fuel rod. During creep a recovery of the radiation damage can occur that can affect the subsequent mechanical properties. The mechanical behavior of the cladding has been investigated in laboratory on two neutron irradiated cladding materials: fully recrystallized Zr-1%Nb and stress relieved Zircaloy-4. Creep tests under internal pressure were conducted at 400°C and 420°C. After depressurization and cooling, ring tensile tests were carried out at room temperature. In addition, Transmission Electron Microscopy observations have been performed after testing. The post-creep mechanical response exhibited a decrease of the strength compared to the asirradiated material. This decrease is associated with a significant recovery of the ductility, which becomes close to the ductility of the unirradiated material. The Transmission Electron Microscopy examinations, especially conducted on recrystallized Zr-1%Nb ring samples, revealed that the radiation defects have been annealed. It was also observed that, as for the unirradiated material, the deformation occurred homogeneously throughout the grains. No dislocation channel was indeed observed contrary to the as-irradiated material. These observations explain the recovery of the strength and of the ductility after post-irradiation creep that may occur during dry transportation or at the beginning of dry storage

Tres estudios sobre el movimiento obrero en México

En las últimas décadas México se ha transformado de un país eminentemente agrario en una nación en proceso de industrialización. En 1930, casi las tres cuartas partes de la fuerza de trabajo se encontraban en la agricultura; en 1970 la proporción se había reducido a menos del 40%. Correlativamente ha aumentado la proporción de la población activa en el sector manufacturero, la construcción, el comercio y los servicios

Magic Number Pt₁₃ and Misshapen Pt₁₂ Clusters: Which One is the Better Catalyst?

A relationship between the size of metal particles and their catalytic activity has been established over a nanometer scale (2–10 nm). However, application on a subnanometer scale (0.5–2 nm) is difficult, a possible reason being that the activity no longer relies on the size but rather the geometric structure as a cluster (or superatomic) compound. We now report that the catalytic activity for the oxygen reduction reaction (ORR) significantly increased when only one atom was removed from a magic number cluster composed of 13-platinum atoms (Pt₁₃). The synthesis with an atomic-level precision was successfully achieved by using a dendrimer ligand as the macromolecular template strictly defining the number of metal atoms. It was quite surprising that the Pt₁₂ cluster exhibited more than 2-fold catalytic activity compared with that of the Pt₁₃ cluster. ESI-TOF-mass and EXAFS analyses provided information about the structures. These analyses suggested that the Pt₁₂ has a deformed coordination, while the Pt₁₃ has a well-known icosahedral atomic coordination as part of the stable cluster series. Theoretical analyses based on density functional theory (DFT) also supported this idea. The present results suggest potential activity of the metastable clusters although they have been “missing” species in conventional statistical synthesis

High fidelity simulation and ECMO in intensive care unit. A multi profesionnal training program to improve skills and self efficacy

International audienc