This is a big boi cargo ship we're talking about, the kind so large that it can't "blast off" - it has to be built in space and stay there. It is definitely not death-star sized. Let's say it's as big as a star destroyer.
Unfortunately, in this scenario, space pirates or an enemy force or a natural disaster cause its engines to be damaged but not its cargo, and it begins to fall into the Earth-like planet around which it was orbiting.
This ship's cargo happens to be nuclear weapons.
Do the weapons go off when it hits the ground, and if so, what kind of damage do they do compared to if the same amount of weapons had been launched in an attack?