Weren’t both Chernobyl and Three Mile Island cases of reactor control exercises gone wrong?
Hard to design for that. The more safety you design in, the more extreme the “testing” becomes. Or so it seems to me.
No, Chernobyl and TMI, except for both being nuclear power plants, were completely different in design and cause.
Chernobyl was destroyed by operator error at the end of reactor testing where the procedure was willfully violated. A steam explosion caused by prompt criticality blew the top of the reactor off.
TMI happened due to a reactor scram, followed by a normal lifting of a steam relief valve on the pressurizer that did NOT reseat, resulting in a sustained loss of coolant/cooling to the reactor core. Operator error played its part in that coolant injection was secured despite indications requiring it to remain in operation. Without cooling, the core was exposed and melted.