“Would an internal collapse without any openings to the outside air release radioactive material?”
I would imagine from the near hysterical acts of the Chinese that the entire area is like crazed glass. Picture that you have a bag full of rocks and bang them with a hammer. The rocks break, but the bag holds them in. A major collapse would almost certainly cause the radioactive material now trapped to be blown high into the sky. Picture an entire, hollow mountain collapsing. The air and all the dust would fly upwards and prevailing winds would, apparently, blow it over China. Fat Boy (the MK leader)has tacitly acknowledged the Chinese concern by stating that the next H-bomb test would likely be held over the Pacific. If that’s the case, you have to wonder why they had two hundred people working in the tunnel. But, communist organizations are driven by the need to keep people busy and employed, not to make a profit.