The latest JAIF posting of pressures and temperatures inside the three damaged RPVs at Fukushima continues to suggest that only unit #1 experienced a complete core-relocating meltdown. Units #2 and #3 RPV temperatures indicate severe melting of core materials, but not a full meltdown in either case. Here’s why. The faster water flows through any heat producing system, the lesser the amount of heat the water removes as it passes through. The slower the flow, the greater the amount of heat absorbed as it passes through. With the entire fuel cell of unit #1 completely melted and relocated, there is literally nothing to obstruct the flow of water through the core barrel where the fuel used to be. It’s not there anymore. The water flows through rather rapidly and picks up minimal heat from the corium (solidified mixture of uranium and other core metals). Please keep in mind that unit #1 has 60% less fuel in its core than units #2 and #3, and decay heat has dropped to perhaps one MWth. Unit #1 RPV temperature is at 26oC. On the other hand, unit #2 temperature is at 52oC and unit #3 temperatures are between 47-55oC. The higher temperatures strongly indicate there are some pretty severe flow restrictions in and around the core barrel. This demonstrates that for units #2 and #3 some or most of the damaged fuel has not relocated and remains inside the core barrel! The unmelted portion in each RPV is unquestionably deformed, blocking possible water flow pathways. This slows the flow and allows the water itself to pick up more heat than would otherwise be the case. Thus, government, TEPCO, and news media reports of full, core-relocating meltdowns for all three reactors are probably incorrect. With unit #1…without a doubt! With unit #2, probably not. With unit #3…possibly not.