Good points 500N. Residual rad would deny the area for (effectively) ever. Plus, so would a "bunker buster". Remember that Chernobyl and Fukushima weren't nuclear explosions, just explosions that threw a lot of nuclear material out of its hole. So the 15 Ton Big BLU in the right place would (potentially) have the same effect. But only on the sites that held significant nuclear inventory.
Like you, I ask if the Big BLU is now out of the frame?
Courtney