http://www.japantoday.com/mobile/view/melted-nuclear-fuel-likely-settled-at-bottom-of-crippled-reactorsFriday 15th April, 02:25 PM JST
Nuclear fuel inside the crippled reactors at the Fukushima Daiichi power plant has partially melted and settled at the bottom of pressure vessels in the shape of grains, according to an analysis by the Atomic Energy Society of Japan made public by Friday.
The academic body’s panel on nuclear energy safety has said the melted fuel at the No. 1 to 3 reactors has been kept at a relatively low temperature, discounting the possibility that a large amount of melted fuel has already built up at the bottom of their reactor vessels given the temperature readings there.
A large buildup of melted nuclear fuel at the bottom could become a molten mass so hot that it could damage the critical containers and eventually leak huge amounts of radioactive material.
The panel has also said that the fuel grains with a diameter of between several millimeters and 1 centimeter are believed to have settled flatly at the bottom of the vessels, leaving almost no possibility of a nuclear chain reaction called ‘‘recriticality.’‘ more at link