As I understood it (when discussing it with someone in the know), was that it was likely caused by zirconium in the fuel-rods reacting with water.
This hydrogen should be taken care of, but without (enough?) electrical power levels of hydrogen gas builds up.
This does not mean that containment is broken, or that there is an imminent danger to outsiders. But it is a very serious situation, especially since there seems to be at least two more reactors in similar situations at Fukushima Daiichi.
This hydrogen should be taken care of, but without (enough?) electrical power levels of hydrogen gas builds up.
This does not mean that containment is broken, or that there is an imminent danger to outsiders. But it is a very serious situation, especially since there seems to be at least two more reactors in similar situations at Fukushima Daiichi.
(http://www.world-nuclear-news.org/RS_Battle_to_stabilise_ear... also refers to a problem at Fukushima Daini.)