Depends on how it's done. If they do it the dirty bomb way and winds are unfavorable, sure it could happen, but they'd have to basically set off their own nuke in the plant to make a cloud that would significantly affect anyone outside Ukraine. If they just let it melt down, probably not but it'll wreck the plant and the area immediately nearby.

Still, couldn't hurt to pick up a pack or two of iodine tablets just in case.