Agreed, pop is probably the wrong word. But if the demon core incidents are anything to go by [0], then I can well imaging an unsuspecting worker putting one mo

Agreed, pop is probably the wrong word. But if the demon core incidents are anything to go by [0], then I can well imaging an unsuspecting worker putting one more block of U238 onto a stack, and feeling a sudden wave of heat and seeing a flash of blue light. And then if they don't have the ability to shove the pile over into a more favourable geometry, seeing the whole pile start to melt into a puddle (which would thankfully also have a more favourable geometry). And then dying of acute radiation syndrome a week later. (Seriously, kids, don't try this at home.) Extreme heat will moderate the reaction to some extent, because the expansion of the metal means it is further apart and therefore has lower reactivity, however the temperature at which it stabilises could well be above the melting point of Uranium. [0] https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core