A scenario in which a nuclear reactor meltdown in North America would theoretically melt a hole straight through the Earth to China (which is impossible). In more realistic usage, it describes such a meltdown reaching groundwater and forcing subsequent radioactive gases into the atmosphere. The latter scenario was used as the basis of a 1979 film of the same name starring Jack Lemmon and Jane Fonda. While many advocate nuclear power as clean and safe, the risk of catastrophes such as China syndrome make me very nervous about its use.