A modern nuclear plant is not a bomb, and cannot be made into a bomb without a lot of work.

Just laying down mines and structural charges might not actually be enough to spread radioactive material outside the plant. See, modern nuclear plants are designed in such a way that they can survive a direct strike from a small missile without breaking containment. The reactor itself will be inside a giant steel tank, which is surrounded by a 3-meter thick, lead impregnated concrete wall.

What it will do is render the plant inoperable, meaning that there will be no power, and there will be a long, expensive cleanup of the plant itself.

There's a lot of sensitive shit that can easily be broken. Turbines, cooling lines, that reactor casing itself, the inside of the reactor if anyone is brave or stupid enough to put a bomb there, and all sorts of other places that would render the building into a scrap heap.

As a note, a bomb inside the reactor itself would be bad, but not necessarily "cause a meltdown" bad, not unless the people planting the bomb knew exactly how to set things up.

That said, trashing the inside of the reactor would make things incredibly difficult to recover from. Like, do a full cleanup, tear the plant down to the ground and rebuild it from there. (because of that steel pressure chamber and massive concrete block).

Anyway, the tldr; this is bad, but not regionally bad unless you live in the region and get electricity from this plant. It will also suck balls to clean up.