On the importance of control assembly layouts in standing wave B and B cores

This study investigates the importance of control system layout in breed-and-burn sodium fast reactor cores with radial fuel shuffling on control system reactivity worth and selected core performance characteristics. Four variations of a single reference core with different control assembly layouts are simulated with Serpent 2. The control assemblies are successively moved away from the core center. It is found that, due to the highly radially peaked power distribution, the location of the control assemblies has a very large effect on the control system reactivity worth as well as a non-negligible impact on the core radial power distribution, criticality, and neutron lifetime. The strong sensitivity to the radial location of the control assemblies suggests that it is desirable for designers of standing-wave breed-and-burn cores to include specific layouts for control assemblies in their initial design iterations. (Author)