Como podem os reatores fusionais de fusão ser perigosos? [fechadas]

Em TOS "The Doomsday Machine" é feito deliberadamente:

[Constellation Auxiliary Control]

KIRK: Spock, listen. Maybe Matt Decker didn't die for nothing. He had the right idea but not enough power to do it. Am I correct in assuming that a fusion explosion of ninety seven megatons will result if a starship impulse engine is overloaded?

[Bridge]

SPOCK: No, sir. Ninety seven point eight three five megatons.

[1] link

E no TNG: "The Nth Degree" parece estar acontecendo acidentalmente:

DATA: The fusion reactors that power the array are extremely unstable. There is a high risk of overload. Blockquote

e mais tarde:

LAFORGE: Each of the telescope's subspace antenna clusters is powered by its own fusion reactor, but a single computer controls them all. RIKER: So all eighteen reactors were affected when the computer was damaged? LAFORGE: That's right. They're starting to overload, and could eventually go critical. The explosion would destroy the Array, and I wouldn't want to be next door when that happens.

[1] link

É teoricamente possível iniciar uma reação em cadeia por meio da queda manual de um pedaço de urânio ou plutônio em outro pedaço de urânio ou plutônio.