3 nuclear reactors melted down after quake, Japan confirms

CNN via Drudge ^ | 6/6/2011 | the CNN Wire Staff

[sefarkas]

Meltdown is a laymen term. There are various metals and ceramics in a power reactor core, each with its own melt temperature. BWR fuel is inside a channel, the bundle of rods is within the channel. The ceramic fuel pellets are within the rods. The channels and rods have a much lower melting point than the ceramic UO2. It is likely that the rods and channels were melted/broken enough to let the ceramic pellets out. Those pellets either will fall to the bottom (the fuel support plate) or get circulated in the emergency core cooling system (including the torus). Depending on which part of the core you are referring to, it is possible for the rods to melt although the fuel pellets remain intact. In the business, we consider the core damaged once the rod (clad) is significantly oxidized or there is a significant change in the geometry of the core — a change in geometry that makes the coolant flow models unreliable.