Nuclear explosions are not essentially a weapon-related activity. All these tests could not have been for development of the bomb alone as then China could not be considered to be a nuclear weapon state. China is technologically much inferior to the other developed states. The truth may be that naivete has not permitted the scientists and thinkers to consider that such large number of explosions are not really meant for development of weapons at all but to push hard at the frontiers of knowledge. The naivete that underground nuclear explosions are cleaner than atmospheric or space explosions need to be rejected.
Underground explosions are pernicious in more than one way.
Only the most simpletons could imagine that the underground tests are conducted in a simple hole in the ground and some seismic and radiation measurements are taken to determine the output of energy. In fact, the underground test cell is a fully instrumented laboratory designed to conduct short and long duration tests. Scientists are talking of many kilometer diameter particle accelerators for studying quarks and gluons but they do not mention publicly that such experiments can be simulated in the core of the nuclear explosion. Most of the parameters of modern Particle Physics, Chemistry and a large variety of metallurgy can only be studied with the range of energies, temperatures, pressures and flux densities available close to a nuclear explosion. Again, high intensity photon experiments can only be conducted close to a nuclear explosion.