Replies

YES, that is correct. For the purposes of generating power from fission - YES. For the concern of meltdown/overheating fuel - NO. that is not correct. That IS how a nuclear reactor works, however a melt condition is NOT how a nuclear reactor works. A melted fuel pile has no rods, it is a pile. Even if it has not enough mass for criticality (power generation), without cooling, it will STILL generate enough heat to melt. Decay heat is why. Not fission. A reactor can be shut down and still, if cooling is lost, melt the fuel. To prevent that there are MANY redundant systems to provide that cooling. Fukushimas downfall was the complete loss of site power, including the diesel generator, resulting in loss of cooling, overheated fuel, hydrogen production from overheated zircalloy cladding, hydrogen explosions, melted fuel. Your understanding of reactor physics is basic and good, but somewhat flawed. Critical is an incredibly mis-used term, especially in 'reactor movies'. It means simply this: An even, self-sustaining fission reaction is occurring. Every single power reactor in the USA, when it is producing power, on the grid is - CRITICAL. It has Criticality. If power (neutron levels) is decreasing, it is sub-critical. If power is rising, it is super-critical. None of which has anything to do with this reactor accident, per se. This heat and overheating that eventually overcame these reactors and fuel pools, where did it come from? The pool has spent fuel bundles in it, no criticality present. There was at least one reactor shut down. Where did the overheat come from? Lack of cooling allowed the overheat. The heat source is the fuel, which has lots of fission products that are highly radioactive. These decays produce heat and lots of it. It is not in any way related to large amounts of mass. One fuel bundle, spent, all by itself in a pool will melt if cooling is lost. The concept of critical mass is not connected here. That is my point.

ok then back to my opriginal point

if the whole thing melts, and gets distributed and spread out through cracks in the earth, won’t it cool off instead of continuing to melt down to the center of the earth as one blob of overheated goo?

(hows that for techinical terms?)