Answer: True
Explanation: The Three Mile Island nuclear incident was a partial meltdown of reactor number 2 of Three Mile Island Nuclear Generating Station (TMI-2) in the USA in 1979.
While the incident began with failures in the non-nuclear secondary system, then a relief valve in the primary system that failed to close, failures were compounded by the initial failure of plant operators to recognize the situation as it was (a loss-of-coolant) due to inadequate training and deficient control room instrumentation (ambiguous control room indicators in the power plant's user interface).