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AbstractAbstract
[en] In the study of any new nuclear reactor, the design of the core is an important step. However designing and optimising a reactor core is quite complex as it involves neutronics, thermal-hydraulics and fuel thermomechanics and usually design of such a system is achieved through an iterative process, involving several different disciplines. In order to solve quickly such a multi-disciplinary system, while observing the appropriate constraints, a new approach has been developed to optimise both the core performance (in-cycle Pu inventory, fuel burn-up, etc...) and the core safety characteristics (safety estimators) of a Fast Neutron Reactor. This new approach, called FARM (Fast Reactor Methodology) uses analytical models and interpolations (Meta-models) from CEA reference codes for neutronics, thermal-hydraulics and fuel behaviour, which are coupled to automatically design a core based on several optimization variables. This global core model is then linked to a genetic algorithm and used to explore and optimise new core designs with improved performance. Consideration has also been given to which parameters can be best used to define the core performance and how safety can be taken into account.This new approach has been used to optimize the design of three concepts of Gas cooled Fast Reactor (GFR). For the first one, using a SiC/SiCf-cladded carbide-fuelled helium-bonded pin, the results demonstrate that the CEA reference core obtained with the traditional iterative method was an optimal core, but among many other possibilities (that is to say on the Pareto front). The optimization also found several other cores which exhibit some improved features at the expense of other safety or performance estimators. An evolution of this concept using a 'buffer', a new technology being developed at CEA, has hence been introduced in FARM. The FARM optimisation produced several core designs using this technology, and estimated their performance. The results obtained show that this innovative feature leads to much higher performing and/or safer cores. The FARM approach has also been applied to a GFR concept using a vanadium cladding. However the large uncertainties involved do not really enable one to evaluate the performance of this promising concept.In summary, the feasibility of a global multi-disciplinary optimization has been demonstrated. Although the resulting method (FARM) is less accurate than the conventional method, it allows fast optimization and permits a large number of cores to be explored quickly, and is ideally suited for the preliminary designs studies before further refinement of the core design. (author)
[fr]
Dans l'etude de tout nouveau reacteur nucleaire, la conception de son coeur est une etape decisive. Or il s'agit d'un probleme complexe, qui couple fortement la neutronique, la thermomecanique du combustible et la thermo-hydraulique. Actuellement cette conception se fait par longues iterations successives entre les differentes specialites. Afin d'optimiser de facon plus globale et complete la conception d'un coeur, une nouvelle demarche appelee FARM (FAst Reactor Methodology) a ete developpee dans le cadre de la these. Elle consiste a etablir des modeles simplifies de neutronique, mecanique et thermo-hydraulique, sous forme analytique ou d'interpolation de calculs de codes de reference, puis a les coupler, de maniere a pre-dimensionner automatiquement un coeur a partir de variables d'optimisation. Une fois ce modele etabli, on peut explorer et optimiser directement de nombreux coeurs, a partir d'algorithmes genetiques de facon a ameliorer leurs performances (inventaire Plutonium en cycle,...) et leur surete (estimateurs de surete pour accidents proteges et non-proteges). Une reflexion a egalement due etre menee pour determiner les performances d'un coeur, ainsi que la facon de prendre en compte la surete. Cette nouvelle approche a ete utilisee pour optimiser la conception de trois concepts de coeurs de Reacteur a Neutrons Rapides refroidi au Gaz (RNR-G). Tout d'abord, la conception du RNR-G a combustible carbure et a aiguilles en SiC a pu etre optimisee. Les resultats ont permis d'une part de demontrer que le coeur de reference issu de la methode iterative etait optimal (c'est-a-dire sur le front de Pareto). D'autre part, l'optimisation a egalement permis de proposer de nombreux autres coeurs, ou en degradant un estimateur de surete ou une performance (sur lesquels des marges etaient disponibles), on ameliore les autres performances. Une evolution de ce concept utilisant la nouvelle technologie du buffer, a egalement ete modelisee dans FARM et optimisee. FARM a ainsi permis de proposer les premieres images de coeur GFR carbure gaine en SiC utilisant la technologie buffer, et d'estimer leurs performances. Les resultats obtenus montrent que cette innovation permet d'atteindre des coeurs beaucoup plus performants et/ou beaucoup plus 'surs' (plusieurs profils de coeurs etant proposes). Une troisieme application de FARM a ete realisee sur un concept de GFR carbure gaine en Vanadium, ou la aussi FARM a propose les premieres images de coeur. Toutefois les grandes incertitudes en jeu ne permettent pas veritablement de conclure sur les performances de ce concept, qui semble prometteur. Ainsi, la faisabilite d'une optimisation globale, couplant les differentes physiques d'un coeur de reacteur nucleaire a ete demontree. Si la methode ainsi obtenue (FARM) est moins precise que la methode classique, elle permet d'explorer et d'optimiser beaucoup plus rapidement (en quelques semaines au lieu de quelques mois) un grand nombre de coeurs et est parfaitement adaptee pour l'etape de preconception des coeurs de reacteurs; d'autres etudes detaillees permettant ensuite d'affiner l'image de coeur retenueOriginal Title
Methodologie d'optimisation d'un coeur de reacteur a neutrons rapides, application a l'identification de solutions (combustible, coeur, systeme) permettant des performances accrues. Etude de trois concepts de coeurs refroidis a gaz, a l'aide de l'approche FARM
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1 Dec 2011; 454 p; [135 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/; Modelisation et Instrumentation en Physique, Energies, Geosciences et Environnement
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