Preparation and characterization of micron and submicron-sized vermiculite powders by ultrasonic irradiation

International audienc

Numerical simulation of HELICOFLEX metallic gasket ageing mechanism for spent fuel

International audienceIn the framework of CEA, GNS and CRIEPI collaboration an experimental program is being carried out, in the CEA Marcoule - TECHNETICS GROUP France joint lab, to assess the long-term use of HELICOFLEX metallic seals in spent nuclear fuel storage casks. Beside an experimental program of 100,000 hours accelerated ageing at different temperatures, a numerical model using finite element analysis has been developed to study seal ageing mechanisms and help the extrapolation of these behaviour to various ageing conditions and seal designs.The studies rely on use of the Larson-Miller parameter to define a time-temperature equivalence that has the advantages to be relevant to describe ageing mechanisms and to be easy to use to study different ageing scenarios. However, this analytical approach faces challenges when seal designs and materials change. Thus, to ensure the model reliability, any seal design change should require additional long term and expensive ageing tests.The presentation presents the latest developments related to HELICOFLEX seals numerical simulation. Indeed, to help the seals behaviour extrapolation for different seal designs, mechanical tests and a specific 3D detailed numerical model has been developed to describe its relaxation mechanisms. This model details the different stages of live of the seal with compression, thermal transient and ageing itself and could be used to assess the evolution of the residual spring-back. The relevance of this simulation is assessed and discussed regarding the available database related to long term ageing tests at different temperatures

Numerical simulation of HELICOFLEXR^R metallic gasket ageing mechanism for spent fuel cask

International audienc

Caractérisation des propriétés des joints en silicone : Application au réacteur ASTRID

National audienceLes réacteurs de 4ème génération à neutrons rapides et a caloporteur sodium sont une des filières d'avenir des réacteurs nucléaires étudiées en France et le réacteur ASTRID doit s'en faire le démonstrateur industriel. Dans le cadre du programme de RetD TECNA, les équipes CEA et TECHNETICS Group France (TGF) du Laboratoire d'étanchéité Maestral (LE) sont impliquées dans la conception de systèmes d’étanchéité pour différentes parties du réacteur experimental ASTRID. Un des volets d'etude concerne les systèmes d’étanchéité des Bouchons Tournants (BT) d'ASTRID.Une solution testée au LE consiste a juxtaposer un joint gonflable accompagnant les phases de levee et de descente des BT et un joint a lèvres massif servant lors des phases de rotation. Ces joints sont constitues d'un silicone C85MC6THT/60 (haute temperature, dureté 60 Sore A).Pour appréhender et caractériser les performances, tant en étanchéité qu'en durée de vie, de cette solution, une etude complete est en cours sur ce silicone et ces joints.Dans un premier temps, des calculs par elements finis ont été menés dans les conditions de service et en condition extreme. Ces simulations ont nécessité au préalable la caractérisation intrinsèque du silicone et la determination de loi de comportement hyperelastique. Ces aspects feront l'objet de la premiere partie de la présentation. Ensuite, une machine d'essai spéciale (diamètre de 2,5 m) a été conçue et mise au point au LE afin de mener la caractérisation des joints dans des configurations proches du reel. Cet équipement dédié permet de tester en étanchéité et en endurance des joints gonflables axiaux et des joints a lèvres rotatifs en statique et en dynamique. Les résultats de ces essais font l'objet de la seconde partie de la presentation

Experimental qualification of rotatable plug seals for Sodium Fast Reactor on a large scale test stand

International audienceIn the framework of the ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) project, the CEA Sealing Laboratory with its partner TECHNETICS (TGF) was involved to propose a new concept of rotating plug seals to replace the commonly used liquid-metal seals. An innovative combination of static, dynamic and inflatable seals in silicone rubber ensuring double tightness-barriers for the cover gas was developed. Following the design phase and materials studies, a dedicated test stand was built to qualify the technical performances of these seals. The large size of the test stand composed of a 2.5m diameter rotating plates was chosen to provide a small profile height on seal diameter ratio, and a volume of enclosed gas large enough to allow representative qualification of leak-test methods. After a description of the test stand, the paper presents the mains outcomes of the technical qualifications (mechanical behavior, sealing performance, endurance test) led on several seals design

Elaboration and characterization of materials obtained by pressing of vermiculite without binder addition

International audienceVermiculite materials were obtained by uniaxial pressing of potassic vermiculite powders obtained by sonication without any binder addition. The vermiculite powders, made of aggregates of particles with nanometric thick-ness and micrometric in plane dimension, were pressed in the range 17.7–80 MPa at room temperature and 200 °C, and further annealed in the range 400–800 °C. Pressing powders at 200 °C instead of 25 °C allowed the slight increase of the density of the formed materials (from 1.9 to 2 g·cm −3) due to the desorption of the water molecules from the interaggregate and interparticle spaces, allowing a higher densification. The density was also increased by tailoring the particle size distribution. The pressed materials were formed of oriented arrangement of vermiculite aggregates. The porous structure, characterized by mercury porosimetry, scanning electron microscopy, and small angle X-ray scattering, was modelled by oriented oblate spheroidal pores formed in the voids between the stacked aggregates organized in a structure possessing a cylindrical symmetry. The porous structure was found to vary with the pressure and the annealing temperature