I’m not sure just how major this is, but in The Oil Drum I read that all three operating reactors at Fukushima suffered fuel meltdowns, and all three apparently have holes in the primary containment vessels which are believed to have been caused by the melted fuel burning through the vessel. Much of the melted fuel remains, however, because the reactors are still generating a great deal of heat.
Water which is being pumped into the reactor vessels to cool them is leaking out, and is being pumped out of the reactor buildings into a storage area nearby. The storage area is filling up, but now they have discovered that the highly radioactive water is leaking from that storage area, too. It is presumably going into the ocean.
What has not been admitted anywhere is that nobody knows how to remove the remaining melted fuel from the reactors. Think about that for a moment.
You can see some really hi-res pictures of the disaster here. Awful.