Géochimie isotopique

Résumé

La géologie isotopique est une branche de la géologie, apparentée à la géochimie, qui exploite l'étude des isotopes stables et radioactifs présents sur Terre pour en étudier la composition et les variations au cours des temps géologiques. À l'origine, la géologie isotopique a consisté à utiliser les connaissances concernant la radioactivité afin de dater des roches et des minéraux. Cette discipline, au carrefour de la géologie et de la physique nucléaire, s'est surtout illustrée par ses méthodes de datation absolue. Elle a ensuite aidé à mieux comprendre la paléoclimatologie, les structures et la dynamique interne du globe. Avec les progrès techniques s'est développée l'étude des isotopes stables, qui a donné accès à l'étude fine des grands processus géologiques, avec à la clé la reconstitution de paléoenvironnements. Géochimie des isotopes radiogéniques L'outillage de base de la géologie isotopique est le spectromètre de masse et comme son nom l'indique cette technique gé

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Publications associées (6)

Are high He-3/He-4 ratios in oceanic basalts an indicator of deep-mantle plume components?

Reto Frei, Anders Meibom

The existence of a primordial, undegassed lower mantle reservoir characterized by high concentration of He-3 and high He-3/He-4 ratios is a cornerstone assumption in modern geochemistry. It has become standard practice to interpret high He-3/He-4 ratios in oceanic basalts as a signature of deep-rooted plumes. The unfiltered He isotope data set for oceanic spreading centers displays a wide, nearly Gaussian, distribution qualitatively similar to the Os isotope (Os-187/Os-188) distribution of mantle-derived Os-rich alloys. We propose that both distributions are produced by shallow mantle processes involving mixing between different proportions of recycled, variably aged (.) radiogenic and unradiogenic domains under varying degrees of partial melting. In the case of the Re-Os isotopic system, radiogenic mid-ocean ridge basalt (MORB)-rich and unradiogenic (depleted mantle residue) endmembers are constantly produced during partial melting events. In the case of the (U+Th)-He isotope system, effective capture of He-rich bubbles during growth of phenocryst olivine in crystallizing magma chambers provides one mechanism for 'freezing in' unradiogenic (i.e. high He-3/He-4) He isotope ratios, while the higher than chondritic (U+Th)/He elemental ratio in the evolving and partially degassed MORB melt provides the radiogenic (i.e. low He-3/He-4) endmember. If this scenario is correct, the use of He isotopic signatures as a fingerprint of plume components in oceanic basalts is not justified. Published by Elsevier Science B.V.

2003

Chargement

EQL3D: ERANOS based equilibrium fuel cycle procedure for fast reactors

Jiri Krepel, Konstantin Mikityuk

The advanced fast reactors of the fourth generation should be capable to breed their own fuel from poorly fissile 238U and to recycle the actinides from their own spent fuel. However, this recycling or actually the closure of fuel cycle has negative impact on the safety parameters. The goal of this work is to develop a numerical tool, which can simulate and confirm the capability of these reactors to operate with closed fuel cycle, and which can evaluate their safety parameters. The tool is named equilibrium fuel cycle procedure for fast reactors (EQL3D) and is based on the ERANOS 2.1 code platform. Equilibrium cycle or virtually equilibrium method for considering the homogeneous recycling of actinides is a known approach; however, in EQL3D the equilibrium method is newly applied for hexagonal-z 3D and r-z 2D core geometries and typically 33 energy-group neutron-flux calculations. The utilization of hexagonal-z 3D geometry enables to characterize the equilibrium cycle for complex reloading patterns within a multi-batch scheme. Furthermore, EQL3D enables comparison of the advanced fast reactors on a common basis of their equilibrium cycle reactivity swing, fuel composition, breeding gain and safety-related parameters. The Gas-cooled Fast Reactor (GFR) was selected for verification and optimization of the EQL3D procedure. The GFR geometry was based on an international neutronics benchmark with a simple setup and potential for latter upgrade. It was used to show the impact of several EQL3D options e.g. different isotope evolution models, geometry selection, or cross-section recalculation frequency, on the equilibrium parameters. The results demonstrate the capability of the procedure to calculate the equilibrium fuel cycle for advanced fast reactors. Among others, also the ability of GFR benchmark core to be operated with closed fuel cycle is shown.

Elsevier2009

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An ancient, highly radiogenic Os isotope reservoir in Earth

Reto Frei, Anders Meibom

2002

Chargement

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Personnes associées (2)

Anders Meibom, Reto Frei

Unités associées (2)

Laboratoire de geochimie biologique

Laboratoire de catalyse et synthese organique

Concepts associés (37)

Isotope stable

vignette|Table des isotopes par mode de désintégration majoritaire (données du programme Nucleus). Un isotope stable d'un élément chimique est un isotope qui n'a pas de radioactivité décelable. Au , 2

Géologie

vignette|Discordance angulaire de Siccar Point (Écosse) où des couches peu pentées de grès rouges du Dévonien recouvrent les formations verticalisées de grauwackes du Silurien. vignette|Carte mondiale

Stable isotope ratio

The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isot

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Cours associés (1)

This course is intended to understand the engineering design of nuclear power plants using the basic principles of reactor physics, fluid flow and heat transfer. This course includes the following: Reactor designs, Thermal analysis of nuclear fuel, Nuclear safety and Reactor dynamics

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