Under certain circumstances, the xenon effect on core reactivity is so substantial that the reactor cannot be restarted for a certain time after shutdown. Also, if control rods are used for power variations, they can deform the axial power distribution and thus create an axial imbalance in 135Xe distribution. Management of these axial power imbalances and oscillations is an additional challenge for operations in load following mode, especially in the case of large power variations.