It would be interesting to test the ‘meltdown’ theory
A sustained nuclear reaction occurs when so much nuclear material is in close contact with more of itself, that it acheives ‘critical mass’- essentially a lump of material so big it heats itself up to the melting point.
If you cram it together suddenly you would have a nuclear bomb.
An actual meltdown could ooze through so many tiny cracks and crevices that eventually the critical mass would be seperated and it would stop
(my theory)
No, not really. A ‘meltdown’ is not really nuclear fission oriented. It is HEAT oriented. Reactor fuel, after shut down, and sub-critical- generates heat from decay of radioactive fission products, hence the need for post shutdowwn cooling and fuel pools.