The possibility of designing a nuclear power reactor to be turned into a bomb (ala star trek core ejection)

so a nuclear reactor has a LOT of fissile material, it does go supercritical (kinda). so if you put some amount of explosive around it, you could make it go big boom, right? You would ofc have to remove all the control rods and maybe pump out the coolant, but otherwise it would be possible? Is there anything that would make this impossible/implausible?