There is no need to worry of nuclear disasters in China, as you will most certainly not hear about it when they happen (even if you live in China). You can’t worry about what you don’t know, and after all everyone eventually dies of cancer…
a major accident would trip geiger counters. that's what happened with Chernobyl. so either you'll detect it, or it won't affect you.
My comment was a bit tongue in cheek… but let’s say you are the weird prepper who (considering the generally poor population) finds money to spare on an actually functioning Geiger counter; what do you think you can really do if it starts beeping?