Despite many denials from the operators of the doomed Fukushima reactors, smart money says that the meltdowns have penetrated the bottom of at least one of the three stricken reactor vessels:

The Nuclear Regulatory Commission speculated Wednesday that some of the core of the No. 2 reactor had flowed from its steel pressure vessel into the bottom of the containment structure. The theory implies more damage at the unit than previously believed... The Nuclear Regulator Commission said that its speculation about the flow of core material out of the reactor vessel would explain high radiation readings in an area underneath, called the drywell.... But some of the radiation readings taken at Reactors Nos. 1 and 3 over the last week were nearly as high as or higher than the 3,300 rems per hour that the commission said it was trying to explain, so it would appear that the speculation would apply to them as well. At No. 2, extremely radioactive material continues to ooze out of the reactor pressure vessel, and the leak is likely to widen with time, a senior nuclear executive said.... Tokyo Electric’s difficulties in providing accurate information on radiation are not a result of software problems, as some Japanese officials have suggested, but stem from damage to measurement instruments caused by radiation because it exceeds the maximum dose that they are designed to measure, the executive said.... "It’s killing the measuring equipment," he said. "They’re blaming it on software — it’s their meters getting cooked."