13 research outputs found
A new structural behavior to perform efficient nonlinear SFR fuel bundle thermomechanical analysis
International audienceA sodium fast reactor (SFR) fuel bundle is usually a strong hexagonal tube containing around 200 fuel pins made of steel. These pins should not touch each other to avoid overheating and damage of the bundle, which constitutes the first confinement barrier. For that purpose a steel wire is often wrapped around each pin from the bottom to the top with a helical shape. This technology maintains a distance between pins and ensures a proper mixing of the sodium, two necessary conditions so as to avoid hot points and damage. Nevertheless the intense fast neutron irradiation induces a significant isotropic swelling and creeping of the pins. If continued, this progressively generates contact closures (phase 1), then mainly a helical bow of the pin (phase 2), and in the end, a strong ovalisation of the cladding sections (phase 3). At such an interaction level, there is a possibility of cladding damage due to thermal creep accumulation. Several 3D finite elements models of the fuel bundle have been developed including the tube, all the 217 pins and their wrapped wires, at least 7.000 contact, with thermal and irradiation creeping laws. If conventional solid or even shell elements are used, then the huge memory cost and CPU time become completely inconsistent with the project expectations. The first analyses have shown that it was necessary to reduce the number of degree of freedom, but also, to keep the representation of all the pins and all the contact areas. Thus, a new approach is used here. First, the helical deformation of each pin is captured by a simple viscoplastic vertical beam; second, a new connecting element is developed and positioned horizontally on every potential contact area, between the neutral fibers of the two adjacent pins concerned. This connecting element, based on a bar finite element with only two nodes, takes into account:-the gap and the contact between a wire and the neighbor pin, or between a wire and the tube,-the thermal expansion and irradiation swelling of the pin and wire cross sections,-the radius increase by creeping under internal pressure loading,-the elastic rigidity of the pin crushing (locally pinching a short section of a tube),-the contact force, altered by the two creeping behaviors, when pinching this 3D tube section,-the counter ovalisation force due to internal pressure,-the hot point stress and strain tensors on the internal skin (strain concentration),-the hot point damage accumulation due to thermal creeping only. The two main difficulties are the following ones:-the damage evaluation supposes a really high precision in the stress tensor calculation, around 1%,-several nonlinear structural effects should be considered in only one integration point. These bar connecting element have been implemented in the Cast3M finite element code (http://www-cast3m.cea.fr). In the end, the bar element is validated by detailed 3D solid calculation. Then, a few relevant bundle experiments, which were conducted in the PHENIX French SFR, are fully simulated. They show good agreement to the measurements and a CPU performance gain between 100 and 1000
Nouvel élément de structure pour les calculs d'interaction dans les faisceaux d'aiguilles combustibles des RNR
International audienceLe faisceau d'aiguilles d'un assemblage combustible de réacteur à neutrons rapides est sujet à plusieurs phénomÚnes qui coupl ent la neutronique, la thermohydraulique, la mécanique, et la science des matériaux. On étudie le cas des aiguilles qui gonflent sous irradiation et peuvent interférer au point de se vriller, s'ovaliser, voir perdre leur étanchéité. Afin de résoudre ce problÚme multi-corps et multi-échelle en un temps raisonnable, on développe dans Cast3M un élément barre de liaison spécifique, à localisation de déformation pour le dommage, prenant en compte le fluage et la pressio
Un élément fini de structure pour les calculs d'interaction et d'endommagement des aiguilles combustibles des RNR-Na
International audienceOn s'intéresse ici à la modélisation de la tenue du faisceau d'aiguilles des assemblages combustibles des réacteurs à neutrons rapides. Soumis à plusieurs phénomÚnes couplant neutronique, thermohydraulique, mécanique et science des matériaux, ces aiguilles gonflent sous irradiation et peuvent interférer au point de se vriller, s'ovaliser, voir perdre leur étanchéité. Afin de résoudre ce problÚme multi-corps et multi-échelle en un temps raisonnable, un nouvel élément fini a été développé dans Cast3M permettant la localisation des déformations/contraintes pour le dommage
CâĂ©tait demain : anticiper la science-fiction en France et au QueÌbec (1880-1950)
LâĂ©criture des futurs possibles nâa pas attendu le xxe siĂšcle pour exister. NĂ©e avec la RĂ©volution industrielle et les progrĂšs techniques, la science-fiction ne sâappelait pas encore ainsi : les rĂ©cits Ă©voquant lâavenir appartenaient Ă la littĂ©rature conjecturale selon le mot de Pierre Versins, Ă la proto-science-fiction, Ă lâanticipation ou au merveilleux scientifique. Entre 1880 et 1950 Ă©merge un continent littĂ©raire français et francophone quâil faut explorer, hĂ©ritier de Jules Verne et contemporain de H. G. Wells. Ce ne sont pas des gĂ©nĂ©rations perdues mais des Ă©crivains Ă la crĂ©ativitĂ© singuliĂšre qui ont su articuler utopie, aventures, science et voyages extraordinaires tout en vivant une fin de xixe siĂšcle dynamisĂ©e paradoxalement par lâessor scientifique et la lame de fond de la PremiĂšre Guerre mondiale. Lâutopie, lâapocalypse, les anticipations technologiques et la fascination pour la science sont les soubassements dâune galaxie littĂ©raire bien prĂ©sente au Canada francophone et en France, diffusĂ©e par un dense rĂ©seau de presse quotidienne et spĂ©cialisĂ©e. De Paul dâIvoi Ă RenĂ© Barjavel, des effets spĂ©ciaux de Georges MĂ©liĂšs aux rĂȘveries cosmiques de Camille Flammarion, cet ouvrage ouvre le champ de la recherche universitaire Ă un domaine inĂ©dit, la littĂ©rature conjecturale dâexpression française des annĂ©es 1880 Ă 1950
Harmonization of the Volume of Interest Delineation among All Eleven Radiotherapy Centers in the North of France.
BACKGROUND:Inter-observer delineation variation has been detailed for many years in almost every tumor location. Inadequate delineation can impair the chance of cure and/or increase toxicity. The aim of our original work was to prospectively improve the homogeneity of delineation among all of the senior radiation oncologists in the Nord-Pas de Calais region, irrespective of the conditions of practice. METHODS:All 11 centers were involved. The first studied cancer was prostate cancer. Three clinical cases were studied: a low-risk prostate cancer case (case 1), a high-risk prostate cancer case (pelvic nodes, case 2) and a case of post-operative biochemical elevated PSA (case 3). All of the involved physicians delineated characteristically the clinical target volume (CTV) and organs at risk. The volumes were compared using validated indexes: the volume ratio (VR), common and additional volumes (CV and AV), volume overlap (VO) and Dice similarity coefficient (DSC). A second delineation of the same three cases was performed after discussion of the slice results and the choice of shared guidelines to evaluate homogenization. A comparative analysis of the indexes before and after discussion was conducted using the Wilcoxon test for paired samples. A p-value less than 0.05 was considered to indicate statistical significance. RESULTS:The indexes were not improved in case 1, for which the inter-observer agreement was considered good after the first comparison (DSC = 0.83 ± 0.06). In case 2, the second comparison showed homogenization of the CTV delineation with a significant improvement in CV (81.4 ± 11.7 vs. 88.6 ± 10.26, respectively, p = 0.048), VO (0.41 ± 0.09 vs. 0.47 ± 0.07, respectively; p = 0.009) and DSC (0.58 ± 0.09 vs. 0.63 ± 0.07, respectively; p = 0.0098). In case 3, VR and AV were significantly improved: VR: 1.71(± 0.6) vs. 1.34(± 0.46), respectively, p = 0.0034; AV: 46.58(± 14.50) vs. 38.08(± 15.10), respectively, p = 0.0024. DSC was not improved, but it was already superior to 0.6 in the first comparison. CONCLUSION:Our prospective work showed that a collaborative discussion about clinical cases and the choice of shared guidelines within an established framework improved the homogeneity of CTV delineation among the senior radiation oncologists in our region
LâImaginaire du temps dans le fantastique et la science-fiction
Le Temps semble a priori irrĂ©versible et lâhomme nâaccepte que difficilement lâeffondrement des possibilitĂ©s de lâavenir dans la fixitĂ© du passĂ©. La science sâest emparĂ©e de cette problĂ©matique puissante dĂšs les annĂ©es trente Ă partir de la thĂ©orie de la relativitĂ© gĂ©nĂ©ralisĂ©e dâAlbert Einstein. Mais bien avant lâapparition de la physique quantique et dâhypothĂ©tiques dĂ©placements dans le temps ou dans des mondes parallĂšles, les littĂ©ratures de lâimaginaire que sont la science-fiction et le fantastique ont parcouru le temps. Cet imaginaire, explorĂ© de façon complĂ©mentaire par le cinĂ©ma, est une machine Ă voyager virtuellement dans des histoires de temps. La science-fiction expĂ©rimente le temps en tant que concept : elle le manipule en tout sens pour briser son irrĂ©versibilitĂ© et tenter dâagir sur des destinĂ©es collectives ou individuelles. La temporalitĂ© fantastique est marquĂ©e par une obsession anxiogĂšne et toxique du temps passĂ©. Le mythe puise ses racines dans un temps immĂ©morial, cyclique. Symbole de la crĂ©ativitĂ© des littĂ©ratures et du cinĂ©ma de lâimaginaire, le temps est au coeur de lâindividu, de sa subjectivitĂ©, de sa mĂ©moire et de son rapport au monde physique
Definition of index used for the delineation comparison.
<p>Definition of index used for the delineation comparison.</p
First comparison of the clinical target volume delineation for case 2 (pelvic lymph nodes).
<p>First comparison of the clinical target volume delineation for case 2 (pelvic lymph nodes).</p