I answered. Refugees would pour into neighbors and China is one of them. Their aversion to refugees presently suggests they dread NK refugees. The NK-China border at 840KM is there times larger than the 250Km demillitarized zone between NK and SK. Bulk of NK population live nearer Chinese border than the demillitarized zone
China has been NK Ally since the Korean war and before but NK pulled a fast one in 2006 when they tested a nuclear weapons. Means the nuclear program was done behind their back for a better part.
Actually you did not. Why would they pour into China or Russia, where they are not wanted, instead of just going South, where they would be welcomed as
full citizens and not refugees?. Saying that the border is longer (actually 1420 km, not your 840) and most of them live up there does not do it; I never heard of (would-be) refugees choosing where to go on such a basis. And then there's this (which you should also relate to the
ease of crossing that long border):
Most North Koreans live in in the south and west of the country, which is largely made up of lowlands. The north of the country, near the border with China, is more mountainous and far less densely populated.
http://worldpopulationreview.com/countries/north-korea-population/(By the way, as far as I can tell, from first-hand observation, the Chinese just don't like
any kind of refugee, and I wouldn't extrapolate that into something special about NK.)
The "fast one" theory too is interesting, given that NK's nuclear ambitions were evident as early as the 1980s. In fact, at one point Little Kim's father invited Westerners to view a plutonium extraction facility. You might also want to look into the IAEA's attempts to properly inspect the Yongbyon complex and their conclusion that NK was most likely working on nuclear weapons Etc. Etc. Etc.. That was in the 1990s. A whole bunch of stuff in the history, and China did not know of any of it? In any case, the issue wa about leverage right now. Are you sure the China, with all the sanctions-busting NK front companies operating there and it being, by a huge margin NK's largest trading partner---doesn't have the leverage to push NK?