New Data on the Origin of Modern Man in the Levant

Anthropolog

The challenge of modeling fuel-coolant interaction Part II - Steam explosion

International audienceIn the course of a severe accident in a nuclear power plant cooled or moderated by water, the core might melt and flow down into the water. Under certain circumstances, a steam explosion might develop during the mixing of the melt and the water. Such an explosion, if occurring in the reactor pit of a PWR or BWR, might challenge the containment integrity and is thus an important issue for nuclear safety. This paper aims at presenting both a status of research and understanding of the phenomenon and the main characteristics of the models developed in the 3-dimensional computer code MC3D. We make a particular emphasis on the underlying difficulties, uncertainties and needs for further improvements. We discuss more particularly the two major phenomena that are the fine fragmentation and the pressurization process. We also give insights on the impact of melt solidification on the fragmentation and on the issue of oxidation. The verification basis of the models is discussed and finally, an example of 3D calculation is presented to highlight the current code capabilities. © 2014 Elsevier B.V. All rights reserved

Capabilities of MC3D to investigate the coolability of corium debris beds

International audienceA nuclear severe accident progression may lead to the formation of a corium debris bed either in the vessel lower head (in-vessel debris bed) or in the vessel pit (ex-vessel debris bed). For safety analyses it is essential to know if a debris bed is coolable or not, i.e. whether a given water mass flow rate poured into the debris bed – either from its top or from its bottom – will be sufficient to evacuate the residual heat and stop the accident progression. The IRSN code, mostly used for fuel-coolant interaction studies, has been modified with the addition of new friction laws for diphasic flows in porous media. The validation of the code in the case of debris coolability concerns the friction in isothermal configuration in cold and hot situations, the evaluation of critical heat flux and the bottom and top reflooding of debris beds. The results obtained with MC3D are in good agreement with the experimental data and are estimated satisfactory regarding to the nuclear safety issues. © 2017 Elsevier B.V

Gestion des ressources lithiques au Paléolithique moyen dans une halte de chasse spécialisée sur le renne : Les Pradelles (Marillac-le-Franc, Charente)

Union internationale des sciences préhistoriques et protohistoriques. International union for prehistoric and protohistoric sciencesInternational audienceIn the lower levels of Les Pradelles, in Charentes, very low densities of lithic artefacts are in contrast with large quantities of bone remains, mostly reindeer. The introduction of finished tools (made on non local, high quality flint from the Cretaceous outcrops) highly curated in the site, together with an expedient strategy on strictly local flint, suggest short term occupations, probably in relation with a “ task specific location ” in a logistical system. Faunal studies confirm this hypothesis. The large bone sample underlines the preponderance of hunting activities repeatedly during the Fall. Intense butchering activities took place on the site as demonstrated by the abundance of filleting marks. Lithic and faunal data indicate that this location should be considered as a seasonal temporary camp devoted to reindeer meet processing for delayed consumption and possibly meat storage.Les niveaux inférieurs du gisement des Pradelles, en Charente, ont livré de faibles densités de matériel lithique qui contrastent avec l'abondance en restes osseux, très majoritairement du Renne. Les études techno-économiques réalisées sur ces assemblages de type Quina ont mis en évidence des stratégies de gestion des matières premières, qui suggérent des occupations de brèves durées en relation avec des expéditions répondant à des besoins spécifiques (task -specific location). Les différences observées dans le traitement des matériaux importés (silex du Crétacé) et celui des matériaux locaux, de moindre qualité (silex du Jurassique) soulignent les capacités d'anticipation des Néandertaliens. La confrontation de ces résultats avec les données archéozoologiques a permis de préciser le fonctionnement de ce site au sein du territoire. En effet, les recherches effectuées sur les restes osseux, très abondants, ont permis de conclure à l'existence probable d'une chasse spécialisée sur le Renne, avec traitement de la viande pour consommation différée. Ce cas d'étude illustre parfaitement la nécessaire complémentarité des approches technologiques et archéozoologiques, entre autres, dans la définition des territoires, fonction des sites et schémas de mobilité des chasseurs-cueilleurs du Paléolithique

The challenge of modeling fuel-coolant interaction Part i - Premixing

International audienceFuel-coolant interaction is a complex mixing process that can occur during the course of a severe accident in a nuclear power plant involving core melting and relocation. Under certain circumstances, a steam explosion might develop during the mixing of the melt and the water and induce a loss of integrity of the containment. Even in the absence of an explosion, studying the mixing phenomenon is also of high interest due to its strong impact on the progression of the accident (debris bed formation, hydrogen production). This article is the first of two aiming at presenting both a status of research and understanding of fuel-coolant interaction and the main characteristics of the model developed in the 3-dimensional computer code MC3D. It is devoted to the premixing phase whereas the second is related to the explosion phase. A special attention is given to major difficulties, uncertainties and needs for further improvements in knowledge and modeling. We discuss more particularly the major phenomena that are melt fragmentation and film boiling heat transfer and the challenges related to modeling melt solidification and oxidation. Some highlights related to the code verification are finally given. © 2014 Elsevier B.V. All rights reserved

New climatic approaches to the analysis of the middle Paleolithic sequences: Combined taxonomic and isotopic charcoal analyses on a Neanderthal settlement, Les Canalettes (Aveyron, France)

Over the last decade, several studies have indicated the potential for the δ13C isotope signal of charcoals to act as a new local paleoclimatic/paleoenvironmental proxy, complementary to taxonomic analyses. These studies mainly focused on archeological charcoal from the Holocene series, but the potential of the method to be applied Pleistocene sequences is still under debate. Understanding climate-driven variability in stable carbon isotope ratios of modern samples is fundamental for the accurate characterization of past climate information based on the δ13C of charred material. In a previous study, we laid the methodological foundation to apply the method to Pleistocene contexts. Here, we present the δ13C isotopic signal from Pinus spp. charcoal in a well stratified middle Paleolithic site: “Les Canalettes” (Aveyron, France). We demonstrate that the use of isotopic analyses on ancient charcoal of the genus Pinus from the quaternary period could provide a reliable paleoclimatic marker with high resolution and provide data that is complementary to taxonomic studies. A continuous increase in humidity is observed, with a warming episode identified at the top of the sequence. These results place the occupation of the site in a less rigorous phase at the beginning of MIS 4 and underline the importance of the Causses in the mobility system of several generations of Neanderthals