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A prototype torsional vibration monitoring system has been installed on two reactor coolant pumps at Tennessee Valley Authority Sequoyah Power Plant Unit 1 nuclear reactor for shaft crack monitoring. The system uses a change in torsional natural frequencies as a diagnostic feature since as a crack grows the shaft line torsional dynamics change commensurately. For effective diagnostic monitoring, it is critical to know the inherent feature variation resulting from the instrumentation and data processing. The integrated nature of the prototype hardware/software system and the inaccessibility of the equipment inside the reactor containment building make it impossible to evaluate the measurement capability in a traditional instrumentation chain approach. Hence, a simulation-based evaluation was performed to determine the cumulative effect of the measurement system on the uncertainty in the torsional natural …