Which of the following is a method used to create a uniform flux distribution in a reactor core?

The use of burnable poisons is a recognized method for creating a uniform flux distribution in a reactor core. Burnable poisons are materials that absorb neutrons and are placed in the core at the beginning of the fuel cycle. As the reactor operates, these poisons gradually degrade or are consumed through fission reactions, which allows for better control of the reactivity throughout the cycle. By managing the neutron population and absorption rates in different regions of the core, burnable poisons can help flatten the power distribution and prevent hotspots, thereby achieving a more uniform flux distribution.

In contrast, high-grade uranium typically refers to uranium with a high percentage of the fissile isotope U-235, which may contribute to higher reactivity but does not inherently stabilize or uniform the flux distribution throughout the core. Increasing the core temperature can influence reactivity and can affect thermal conditions within the reactor, but it does not directly contribute to achieving a uniform neutron flux. The use of neutron reflectors can improve overall reactor performance by reflecting escaping neutrons back into the core, but its primary function is not to ensure uniformity of the neutron flux across the core effectively.