Well, how about a 500 kg shaped charge?

And you can just remove the control rods and wait for it to melt on its own (meltdown-proof fuel isn't actually, well, proof). You'll get a nice contamination with volatiles (cesium and iodine), for the bonus points you can wait until the end of the fuel campaign to maximize the amount of transuranics.

I just don't think this is a viable option, except for very niche scenarios.