Which of the following is listed as a type of reactivity control accident?

• A. Rod ejection accident.
• B. Normal reactor shutdown.
• C. Routine fuel reload.
• D. Cooling system maintenance.

Answer: (A)

The key idea is events that cause an unintended change in core reactivity due to the control system. A rod ejection accident fits this exactly: if a control rod is suddenly ejected, positive reactivity is rapidly inserted into the core, driving a quick rise in reactor power. This is the classic example of a reactivity control accident because it hinges on unintended movement of the control mechanism and the resulting reactivity insertion, which must be countered by rapid safety actions like a scram.

The other scenarios are not accidents or not tied to uncontrolled reactivity changes. A normal shutdown is a planned action to reduce reactivity and stop the reactor; routine fuel reload is a scheduled change that alters reactivity under controlled conditions; cooling system maintenance involves heat removal and upkeep, not an unintended reactivity event.