Reports from Japan indicate an explosion and smoke coming out of their nuclear plant.
OK, smoke coming out of a troubled nuclear plant does not sound like good news. It might be steam, which isn't good news either. If hot molten metal drops into a pool of water, the result can be a steam explosion. A melted down core would be hot molten metal.
This may very well mean that the containment has been breached.
OK, I just found some video and it looks like a BIG explosion. NHK is reporting that the walls and roof of a building at the site have collapsed. This looks like a Chernobyl style release. The only good news here is that the cloud seems to be heading out to sea.
1.17am Well at least California is 5000 miles east of Japan. I was in Europe in 1986 when Chernobyl blew, and it wasn't all that big a deal in Britain. Some milk and cheese had to be thrown out, but we didn't all get irradiated. Hopefully this cloud will disperse out over the Pacific without bothering anybody. I'm sure the Pentagon has a program to predict nuclear fallout, and they might want to get that fired up and try to predict where this cloud is headed.
1.50am I remember seeing this a couple of hours ago: 'Japan's nuclear agency says radioactive cesium is detected in the air near one plant'
When Uranium reacts in a nuclear reactor Cesium is one of the products.
If this stuff is coming out it probably means severe heat damage to the fuel, which could mean that it has melted.
( Edit, Sunday, March 13 : Fortunately no major radiation release resulted from this event, but it looked really bad at the time. 'Explosion' and 'Nuclear Reactor' are words you don't want to see in the same sentence!)