Figure 36 - from "Conception de réacteurs à neutrons rapides à effet Doppler renforcé : Conception, mise au point de schémas numériques, évaluation des incertitudes"

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Figure 1.1: Global electricity generation by source in years 1990-2015 [1] The constantly increasing energy demand, depletion of natural resources and threat of global warming are some of the major challenges facing the energy sector in the 21st century. The world is currently experiencing an increasing need for development of sustainable, low-carbon energy sources as a core of the future energy supply.

Figure 1.2: Average number of neutrons produced per each neutron absorbed (often referred to as reproduction factor or 7) as a function of incident neutron energy. The values are given for three types of fissile isotopes considered to be best choices for nuclear fuel. In the fast energy range the highest 77 is exhibited by 7°°Pu. By efficiently using the surplus neutrons, the breeding ratio BR, defined as a ratio between number of fissile nuclei produced to fissile nuclei destroyed, can reach values higher than in any available thermal reactor technology. In some fast reactor designs the BR higher than one can be achieved, meaning that the amount of fissile material in the reactor increases over time. The high value of BR increases the maximum possible fuel burnup by burning

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Figure 1.3: Simplified scheme of SFR with descriptions [11]. 1.5 Criticality and delayed neutrons .5.1 Neutron multiplication via chain reactio1 1.5 Criticality and delayed neutrons

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$Table 1.1: Six groups of delayed neutrons emitted during the fission of 7°°Pu [14] The amount of reactivity provided to the system by the delayed neutrons alone is called effective delayed neutron fraction Gog. In general Bo¢ 4 G6 since, on average, the delayed neutrons are born with lower energies than the prompt neutrons. In fast reactors, bog tends to be lower than 3, as in such a configuration the delayed neutrons are slightly less likely to multiply than the prompt neutrons.$

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Maciej Zajaczkowski

Conception de réacteurs à neutrons rapides à effet Doppler renforcé : Conception, mise au point de schémas numériques, évaluation des incertitudes

Abstract: Afin d'améliorer la sûreté passive des réacteurs rapides refroidis au sodium (SFR) en cas de transitoires non protégés, tels que la perte de débit non protégée (ULOF) ou une insertion de réactivité (UTOP), le CEA a proposé le concept CADOR - une nouvelle conception du cœur SFR avec un effet Doppler renforcé. L'une des caractéristiques de conception la plus importante est l’implantation de modérateur dans chaque assemblage combustible pour diminuer l'énergie moyenne des neutrons d'environ 40%. La solution conduit à un effet Doppler environ trois fois plus élevé en raison de l'augmentation de la population de neutrons dans les résonances. D'autre part, le spectre neutronique adouci modifie d'autres propriétés du cœur. Par exemple, le placement hétérogène du modérateur dans l'assemblage peut entraîner une distribution inégale de la vitesse de réaction et un risque de pics de puissance non observés dans les SFR standard. Pour démontrer la sûreté du concep...

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