What does burnup refer to in reactor operation?

What does burnup refer to in reactor operation?

• A. Increase in fuel enrichment
• B. Depletion of fissile material reducing reactivity
• C. Increase in coolant temperature
• D. Increase in moderator density

Answer: (B)

Burnup is a measure of the energy produced per unit mass of fuel and, in practice, tracks how much of the fuel has been consumed during operation. As burnup increases, the fissile material such as U-235 is depleted and fission products that absorb neutrons build up. Those neutron-absorbing products act like poisons, making it harder for the reactor to sustain the same rate of fission. The net effect is a reduction in reactivity over time, unless adjustments are made (like refueling, changing enrichment, or altering control settings) to compensate. This concept is distinct from simply increasing enrichment, or changing coolant temperature or moderator density, which describe operating conditions rather than the cumulative consumption of fuel.

Burnup is a measure of the energy produced per unit mass of fuel and, in practice, tracks how much of the fuel has been consumed during operation. As burnup increases, the fissile material such as U-235 is depleted and fission products that absorb neutrons build up. Those neutron-absorbing products act like poisons, making it harder for the reactor to sustain the same rate of fission. The net effect is a reduction in reactivity over time, unless adjustments are made (like refueling, changing enrichment, or altering control settings) to compensate. This concept is distinct from simply increasing enrichment, or changing coolant temperature or moderator density, which describe operating conditions rather than the cumulative consumption of fuel.