Neutronic and fuel cycle comparison of uranium and thorium as matrix for minor actinides bearing-blankets

• The use of thorium as support matrix for minor actinides heterogeneous transmutation is investigated.
• Neutronic and fuel cycles performances are evaluated and compared for various reprocessing strategies.
• The impact of reusing 233U in the transmutation targets is evaluated.
• The relative performances of each approach are discussed.

Minor actinides transmutation is one of the three main axes defined by the 2006 French law for nuclear waste management, along with long-term storage and use of a deep geological repository. In the heterogeneous approach, minor actinides are loaded in specially designed targets assemblies which are located in the periphery of the core, in order to limit the impacts on core operations. In this paper, we compare the use of uranium and thorium dioxide as support matrix in which minor actinides are diluted in the target assemblies. Both UO2 and ThO2 exhibit sufficiently good irradiation behavior to withstand the long residence time associated with heterogeneous transmutation. Five different reprocessing strategies are compared in which some or all the elements in the blankets are reused after reprocessing. The impacts on core safety parameters and fuel cycle parameters are also evaluated for each case and it is found that using thorium as support matrix with reuse of uranium 233 leads to transmutation performances similar to the one obtained with the reuse of plutonium from uranium blankets with slightly lower global impacts on reactor operation and fuel cycle.