It was an explosion, but it didn't emit any radiation

Sounds to me like the yield of a half ton of Mentos and a fifty gallon drum of Coke.

NORTH KOREA shook the world's political leaders with some sort of blast on Monday, but no one could say for sure yesterday that it really was a nuclear explosion.

"It was explosion-like … That's all we are saying," said an Australian Government source, who asked not to be named. "It could have been a small nuclear explosion, it could have been a chemical explosion." The blast was simply "too small to classify what caused it. Whether it was nuclear or not, we don't know."

Everybody is crawfishing on the nuclear claim. It's beginning to appear more and more like a "conventional" explosion or a nuclear dud.