David wrote:
As I think Lars has already responded, your outer building needs to be able to withstand aircraft. That can be done by thick walls or alternatively an array of heavy gauge wires above the building that shred any incoming aircraft. A simple berm of soil over your structure or indeed moving underground also works.
D.L.
From what I've read, it seems that an airplane itself is not a good battering ram; basically, it's a light tube. It's the engines that do the battering. So, although it's a cute idea to shred an airplane with heavy gauge wires, it's not clear to me that the wires could shred the heavy engines. However, as others have said, a LFTR is small enough that it and its containment building could easily be buried in which case only the cap would need to be able to withstand the impact from an airplane or missile. And, if it were buried, it would be hard to pinpoint its location from the air.