Excess reactivity is defined as the amount of reactivity that would exist if all control blades were moved to the maximum reactive condition from keff = 1, without credit for which effects?

Excess reactivity is defined as the amount of reactivity that would exist if all control blades were moved to the maximum reactive condition from keff = 1, without credit for which effects?

• A. Negative experiment worth, temperature effects, or xenon poisoning
• B. Positive worth only
• C. Mechanical vibrations
• D. Cooling issues

Answer: (A)

Excess reactivity is the amount of reactivity that would exist if all control blades were moved to the maximum reactive position from a state of keff = 1, without crediting certain negative reactivity effects. In other words, it measures the available reactivity margin ignoring reductions caused by these specific factors: the negative worth from experiments, temperature effects, and xenon poisoning. This framing gives a worst‑case picture of how much reactivity could be added before reaching criticality, which is why those particular effects are not credited in the calculation. If you tried to include any of those negative effects as already present, the measured margin would be smaller, and that would not reflect the pure available excess reactivity. Mechanisms like mechanical vibrations or cooling issues aren’t part of this static reactivity balance, so they don’t define excess reactivity.

Excess reactivity is the amount of reactivity that would exist if all control blades were moved to the maximum reactive position from a state of keff = 1, without crediting certain negative reactivity effects. In other words, it measures the available reactivity margin ignoring reductions caused by these specific factors: the negative worth from experiments, temperature effects, and xenon poisoning. This framing gives a worst‑case picture of how much reactivity could be added before reaching criticality, which is why those particular effects are not credited in the calculation. If you tried to include any of those negative effects as already present, the measured margin would be smaller, and that would not reflect the pure available excess reactivity. Mechanisms like mechanical vibrations or cooling issues aren’t part of this static reactivity balance, so they don’t define excess reactivity.