You have it all wrong. Jane Fonda movie did not have any similarity to TMI except that both plants in the end had core melt.
TMI was caused by the failure to close of a reactor coolant system relief valve on the pressurizer. It caused the coolant reactor coolant system to start losing water slowly. This caused the safety injection system to turn on the emergency water supply. However, this caused the pressurizer go solid (collapse of the steam control bubble). There was no indication that the relief valve was stuck open. The reactor operators have been trained to never let the steam bubble collapse in the pressurizer by their operating procedures developed by the reactor manufacturer (B&W).
To make a long story short, the operators were confused, the reactor supplier (B&W) experts were confused, and the NRC experts were confused. Eventually the operators did turn off the safety injection system but the water level kept going lower.
This small break accident had never been designed for by the reactor manufacturers or postulated by them or the NRC. The reactor core was about half melted when the were able to get water flow back into the reactor via another system to stop the melting.
I can provide NRC documents that detail the whole series of events. However, I think they go above the layman’s head.
Eventually the NRC and the reactor suppliers agree that they must design their plants to recognize and mitigate the consequences of a small loss of coolant accident (LOCA). Before this accident, reactor suppliers designed their plants to recognize and mitigate the consequences of a large loss of coolant accident (LOCA).