Fuel Rods in Rapidly Drying pools causing radiation

[undeterred]

BBC News: New fire hits Japan nuclear plant

It appears that for the first time, the containment system around one of the Fukushima Daiichi reactors has been breached. Officials have referred to a possible crack in the suppression chamber of reactor 2 - a large doughnut-shaped structure, also known as the torus, below the reactor housing.

That would allow steam, containing radioactive substances, to escape continuously. This is the most likely source of the high radioactivity readings seen near the site in the middle of Tuesday. Under normal circumstances, the suppression chamber stores a large volume of water that can be used to condense steam produced in the reactor.

The industry newsletter World Nuclear News reports that a "loud noise" came from the reactor chamber, and that "the pressure... was seen to decrease from three atmospheres to one atmosphere after the noise, suggesting possible damage".

This pressure drop is consistent with the chamber cracking and releasing steam. Once de-pressurised, material would probably be ejected at a slower rate. This is consistent with the swift fall in readings taken around the plant later in the day. Another possible source was a fire and explosion in the building housing reactor 4.

http://www.bbc.co.uk/news/science-environment-12745186