Tokyo - An extendable robot began a two-week mission Tuesday to retrieve the first sample of melted fuel debris from inside one of three damaged reactors at the Fukushima Daiichi nuclear power plant.

Commercial nuclear reactors all work pretty much the same way. Atoms of a radioactive material split, emitting neutrons.

Core disruptive accidents (CDAs) in sodium-cooled fast reactors represent a severe class of events in which the integrity of the reactor core is rapidly compromised, leading to the dispersal of molten ...