Sentence:  The molten mass did not even fully penetrate the 0.5-cm cladding, confirming tests in Karlsruhe, Germany, and in Idaho, that the "<WSD>China syndrome</WSD>" is not a credible possibility. 
Meaning of the word marked with <WSD> tags:  A hypothetical kind of catastrophic failure in which a nuclear reactor melts through the floor of its containment system and penetrates the Earth's surface, continuing downward as if (from a Western Hemispheric point of view) traveling through the planet toward China.