Identify the factors contributing to the TMI accident beyond the cooling malfunction.

• A. Mechanical failure, compounded human errors, and poor valve indication design.
• B. Only operator error with no equipment failure.
• C. Software glitch in safety system.
• D. External power supply outage.

Answer: (A)

This item shows that the Three Mile Island event was the result of multiple interacting problems, not just a single cooling failure. A mechanical fault in components that affect coolant pathways contributed to the loss of coolant. At the same time, operators faced misleading or incomplete information because the valve and instrument indicators didn’t clearly show what was actually happening, making it hard to judge the plant state. Human actions then compounded the situation through misinterpretation, delayed or inappropriate responses, and procedures that didn’t adequately account for the degraded, information-poor situation.

These factors—equipment issues, how information was presented to and interpreted by operators, and imperfect procedures—together explain a much more complete cause than attributing it to a single cause. The other choices don’t fit because they either isolate blame on one element, cite a feature (software) that wasn’t a factor, or point to an external outage that wasn’t the root issue.