It would be worth laying out the sheer violence necessary. The DTIC will happily help you out. You're looking for damage category B (perforation), thickness of slab over a meter. It appears that a 22kg shaped charge will perforate a 1.2m reinforced concrete wall. We're on beyond ammonia weapons here, by the way, although Tim McVeigh kinda sorta shaped the OKC bomb. He also had 6200lbs of "energetic materials" or 5,000lb of TNT (2.5kT for those keeping track at home).

Turkey Point, bless their hearts, has a cutaway of their setup:

So. to perf the reactor vessel in a properly showy fashion you have to broach:

- 3-4 feet of reinforced concrete. Clearly, our 22kg shaped charge will do that.

- 2 inches of steel. not tough at all in splendid isolation, more challenging when surrounded by concrete.

- an air gap. Excellent for dissipating kinetic energy.

- 3-7 feet of concrete shielding. between 25 and...? worth of explosive, after the concrete, the steel and the air gap.

- Another air gap.

- 8-9 inches of steel.

So... it's certainly possible to do this level of damage. You might be able to do it with a ryder truck full of explosives. But you're effectively trying to break open a bank vault in a concrete bunker in a bank vault in a concrete bunker. Set aside for a moment the fact that you're the master of the universe if you can sneak this level of malfeasance next to a reactor. Mad props. A bigger concern, I think, is that any anticipated fallout pattern is going to be highly sensitive to the style of breach. I think (not sure, but think) you're in bunker-buster territory and most of your dissipation is going to be from the primary breach event. At which point it isn't even really a "reactor" question anymore, it's an "impressive amounts of KE" question.