Japan's tsunami-stricken nuclear-power complex came closer to a catastrophic meltdown than previously indicated by its operator [which on November 30] described how one reactor's molten nuclear core likely burned through its primary containment chamber and then ate as far as three-quarters of the way through the concrete in a secondary vessel. The [new] assessment-offered by Japan's government and Tokyo Electric Power Co., ... marked Japan's most sobering reckoning to date of the nuclear disaster sparked by the country's March 11 earthquake and tsunami. But it came nearly six months after U.S. and international nuclear experts and regulators had reached similar conclusions. For the first time, Tokyo Electric ... said that nuclear-fuel rods in the complex's No. 1 reactor had likely melted completely, burning through their so-called pressure vessel and then boring through concrete at the bottom of a second containment vessel. That brought the fuel closer than previously believed to breaching the containment vessel and foundation and continuing to burn through the ground below - a scenario sometimes described as the China Syndrome." The findings are the latest reminder of how much remains unknown about the extent of the mid-March Fukushima Daiichi accident.