I’m pretty sure I heard that from my friend’s parents, too. They were (and are) some of the truly most intelligent people I’ve ever had the pleasure of knowing. I respect them very much.
We were in the training facility which mirrored the actual control room of the plant. The trainer initiated the 3 Mile Island event and after about 3-5 minutes of clicking and clacking of switches and circuits, the test reactor was safely submersed in borax (I believe). The trainer said it’s a scenario that is often taught to trainees.