From www.globalsecurity.org...
Interesting analysis of the problems the North face in doing ANY nuke testing....
According to an analysis by Satoshi Morimoto of Takushoku University, " ... carrying out nuclear tests inside North Korea would be an extremely sticky action. That is because this kind of nuclear testing could only be carried out underground. There is absolutely no way they could do in the air or above ground. Even with underground nuclear testing, you normally need a fifty to sixty kilometer square of desert for a nuclear test. In the U.S., this would be something like the Nevada desert. Unless you have the kind they have in India or Pakistan, you cannot do it. The reason for this is that the underground water system gets damaged. North Korea has a very abundant flow of underground water, and if you carry out an underground nuclear test in this kind of place, radioactive materials would get into the water supply for the whole of the Korean peninsula, and also flow out into the Sea of Japan. As a consequence, if there were any underground nuclear testing in the Korean peninsula, it would not be just the ecological system, but also the topography of the land that would be damaged. So, will they indeed carry out tests? I think they might somehow manage to borrow the Pakistani desert, or else carry out tests in another country. Still, this being North Korea, one can never know. If they did do that sort of nuclear test, then the U.S. would run out of patience."
Just the purest possible horsefeathers. What's to stop them? "Oh, it would pollute". Like they give a rat's tail. They starve their own people to death in the millions without batting an eye.