Characteristics of TRu fueled SFR core during the partial loading of LEU assemblies

The fast reactor in the traditional fuel-cycle analysis is generally assumed to be designed to use U/Pu or U/TRU fuels in either closed or once-through fuel-cycle systems. However, possible situations such as inaccessibility to the TRU based fuel or startup and even complete transition to the U/TRU system need to be furnished with available LEU fuels, in particular those categorized as high-assay LEU. Due to differences in characteristics of LEU and TRU fuels, a partial loading of LEU assemblies within a pool of TRU assemblies may impact on some of safety parameters such as required control rod worth. This paper investigates the impact of partially loaded LEU assemblies within TRU fueled breakeven SFR on fuel-cycle aspects such as transition of nuclide evolutions and core characteristics particularly focusing on uncontrolled burnup reactivity swing.