NUCLEAR, BIOLOGICAL AND CHEMICAL WEAPONS
July 7, 2012: One of the major problems new nuclear powers have is testing their newly developed weapons under realistic conditions. Because of a 1992, treaty, nuclear weapons may no longer be tested, even underground. Before that there was a 1963 treaty that discouraged tests in the atmosphere, underwater, or in space. The last above ground test by China was in 1980.
But until the early 1960s, the United States conducted 331 atmospheric tests, using nukes dropped from bombers, in missile warheads, or even artillery shells. B-52s, for example, dropped 30 live nuclear weapons. The B-29 dropped three (two in combat), the B-45 dropped two, the B-36 six and the F-89 fighter-bomber one. The U.S. Navy fired a submarine launched ballistic missile with a live warhead, as well as testing nuclear depth charges and anti-submarine missiles with nuclear warheads.
Russia, Britain, France, and China also carried out atmospheric tests. But new nuclear powers Pakistan, India, and North Korea have not. They probably won't because of the large quantities of radioactivity such tests put into the global atmosphere.
What all this means is that it's not enough to be able to design and test a nuclear weapon, but you have to deal with all the diplomatic and economic backlash from the rest of the world. This substantially increases the cost of developing workable nuclear weapons. Even computer simulation software has its limitations and obtaining this software, and the hardware that can run it, is not easy.