So, I had this idea for passive safety. Break-apart rods (zirconium with low-melting point metal inserts for example) which go through reactor core at regular intervals, are tensioned by springs, and in the event of overheating, are torn apart, operating simple (springs, latches) mechanisms to ensure insertion of control rods (if not already inserted) and operation of pressure relief and coolant flow valves (relevant to passively cooled reactors), as well as some reliable outside indication of the overheating event. Do any reactors use something of this sort? I know molten salt reactors can use a frozen plug as passive overheating failsafe. I know that various electrical products sometimes use connections that de-solder and disconnect in the event of overheating.