Improvement of minor actinides transmutation performances in gen IV nuclear reactors: fuel cycle and reactors aspects

Minor actinides transmutation is a solution written in the 2006 law on nuclear waste management. One option to carry out transmutation is to recover these heavy nuclides during fuel reprocessing and load them again in reactor cores to achieve fission and obtain shorter-lived fission products. However, minor actinides loading in the nuclear fuel cycle leads to penalties on core transient behavior and fuel reprocessing, such as a modification of core feedback coefficients or a higher neutron source and decay heat of the spent fuel. Following a complete analysis of the transmutation impacts, an optimization methodology of the reactor core taking into account all the fuel cycle and core behavior constraints is developed here. For the heterogeneous mode, where minor actinides are loaded in dedicated targets located at the core periphery, it is shown that the use of light elements to locally moderate the neutron spectrum in the blankets is an optimal solution, even when considering the negative impacts on the fuel cycle.For the homogeneous mode, where minor actinides are directly mixed with the fuel, it is shown that low void cores with axial heterogeneities are not impacted by minor actinides loading for loss-of-flow transients. It is demonstrated that core design results from a balance between core behavior in loss-of flow transient and reactivity insertion transient. Finally, it is shown that regardless of the minor actinides transmutation mode envisaged, fuel cycle constraints were challenging and requires significant R and D in support. (author)