"Is it that nuclear heat is able to make it go faster and provide more reactive force than burning it?" Yes, that is mostly it. Just compare the explosion from

"Is it that nuclear heat is able to make it go faster and provide more reactive force than burning it?" Yes, that is mostly it. Just compare the explosion from some hydrogen with a nuclear bomb. It is all about energy for mass in space, because all the fuel you have, you have to bring up into space, which needs more fuel, so need more fuel to bring that fuel up ... nuclear could help with that mass ratio a lot. And I like the concept in theory - as long as none of them explodes halfway up to space.