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AbstractAbstract
[en] In order to limit the consequences of a hypothetical core meltdown accident in Generation IV Sodium Fast Reactors, absorber materials in or near the core, such as boron carbide B4C, and diluting materials in the core catcher will be used to prevent recriticality within the mixture of molten oxide fuel and molten structures called corium. The aim of the PhD thesis was to select materials of both types and to understand their behaviour during their interaction with corium, from chemical and thermodynamic point of view. Concerning B4C, thermodynamic calculations and experiments agree with the formation of two immiscible phases at high temperature in the B4C - UO2 system: one oxide and one boride. This separation of phases can reduce the efficiency of the neutrons absorption inside the molten fuel contained in the oxide phase. Moreover, a volatilization of a part of the boron element can occur. According to these results, the necessary quantity of B4C to be introduced should be reconsidered for postulated severe accident sequence. Other solution could be the use of Eu2O3 or HfO2 as absorber material. These oxides form a solid solution with the oxide fuel. Concerning the diluting materials, mixed oxides Al2O3 - HfO2 and Al2O3 - Eu2O3 were preselected. These systems being completely unknown to date at high temperature in association with UO2, first points on the corresponding ternary phase diagrams were researched. Contrary to Al2O3 - Eu2O3 - UO2 system, the Al2O3 - HfO2 - UO2 mixture presents only one eutectic and thus only one solidification path which makes easier forecasting the behaviour of corium in the core catcher. (author)
[fr]
Resume: Afin de limiter les consequences d'un accident grave avec la fusion du coeur dans un reacteur a neutrons rapides de generation IV refroidi au sodium, la recriticite doit etre evitee au sein du melange de combustible oxyde et de structures fondus, appele corium. Pour cela, des materiaux absorbants, tels que le carbure de bore B4C, seront utilises dans ou pres du coeur, et des materiaux diluants dans le recuperateur de corium. L'objectif de ce travail est de preselectionner des materiaux parmi ces deux types de familles et de comprendre leur comportement au contact avec le corium. Concernant le B4C, des calculs thermodynamiques et des experiences ont permis de conclure a la formation de deux phases immiscibles dans le systeme UO2 - B4C a haute temperature, une oxyde et une borure, ainsi qu'a la volatilisation d'une partie de l'element absorbant bore. Cette separation de phases pourra reduire l'efficacite de l'absorption neutronique au sein de la phase oxyde. Une solution a ce comportement serait d'augmenter la quantite de B4C ou d'utiliser un absorbant oxyde miscible avec le combustible. Eu2O3 ou HfO2 pourraient convenir car il a ete montre qu'ils forment une solution solide avec UO2. Concernant le materiau diluant, les oxydes mixtes Al2O3 - HfO2 et Al2O3 - Eu2O3 ont ete etudies. L'interaction de ces systemes avec UO2 etant inconnue a ce jour, les premiers points ont ete recherches sur les diagrammes ternaires correspondants. Contrairement au systeme Al2O3 - Eu2O3 - UO2, le melange Al2O3 - HfO2 - UO2 presente un seul eutectique et donc un seul chemin de solidification ce qui permet de prevoir plus facilement la maniere dont le corium solidifierait dans le recuperateur. (auteur)Original Title
Etude des materiaux sacrificiels absorbants et diluants pour le controle de la reactivite dans le cas d'un accidnet hypothetique de fusion du coeur de reacteurs de quatrieme generation
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16 Dec 2010; 240 p; 172 refs.; Available from the INIS Liaison Officer for France, see the 'INIS contacts' section of the INIS-NKM website for current contact and E-mail addresses: http://www.iaea.org/inis/Contacts/; Physique
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ACCIDENTS, ACTINIDE COMPOUNDS, ALUMINIUM COMPOUNDS, BORON COMPOUNDS, CARBIDES, CARBON COMPOUNDS, CHALCOGENIDES, ENERGY SOURCES, EPITHERMAL REACTORS, EUROPIUM COMPOUNDS, FUELS, HAFNIUM COMPOUNDS, LIQUID FUELS, MATERIALS, NUCLEAR FUELS, OXIDES, OXYGEN COMPOUNDS, PHYSICAL PROPERTIES, RARE EARTH COMPOUNDS, REACTOR ACCIDENTS, REACTOR COMPONENTS, REACTOR MATERIALS, REACTORS, REFRACTORY METAL COMPOUNDS, TRANSITION ELEMENT COMPOUNDS, URANIUM COMPOUNDS, URANIUM OXIDES
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