Optimization of minor actinides bearing radial blankets for heterogeneous transmutation in fast reactors
Résumé
A new methodology dedicated to the optimization of minor actinides (MA) transmutation in dedicated blankets is discussed here. In the so-called heterogeneous transmutation approach, minor actinides are loaded in specific assemblies located at the periphery of a fast reactor core. Thus, the resulting perturbation on the core behavior is limited and the management of minor actinides is entirely decoupled from standard fuel management. This also allows greater flexibility in the blankets design, in terms of material, volume fraction or neutron spectrum to be used. On the other hand, the low neutron flux level experienced at the periphery of the core slows down the transmutation process. If this effect can be compensated by an increase of the minor actinides fraction loaded in the blankets, this also strongly increases their decay heat and neutron source level, which complicates spent fuel reprocessing and handling. An optimization is carried out with regards to the neutron spectrum and americium concentration in the blankets, with the dual objective of maximizing the transmuted MA mass while minimizing the total MA inventory in the fuel cycle by limiting the cooling time of such blankets. Artificial neuron networks are coupled with a genetic algorithm in order to reduce total calculations time. It is shown here that regardless of the MA mass to be loaded, the use of a slightly moderated neutron spectrum is the most promising option for heterogeneous transmutation. This result is confirmed by full core calculations. An analysis with regards to the irradiation time is also performed, and it is shown that maximization of the irradiation time should be sought in the specific case studied here. It is concluded that from a purely physical point of view, no breakthrough can be obtained for heterogeneous transmutation.
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