In Status of the Fukushima Reactor Accidents, I said:

… it’s important that everyone realize what I have already said concerning this set of accidents.  The main stream media (both print and television) continue to point towards avoiding a core melt event, as if it will announce itself with some sort of trumpet blast and melt through the earth.  As I have explained, it doesn’t happen that way.  The corium, if it makes it through the lower reactor vessel head, will disperse and cool from that dispersal, not even making it through the lower basemat of concrete.

The cores for Units 1, 2 and 3 are already damaged.  They are partially melted, and partially shattered and rubblized, sitting in the lower part of the reactor vessel.  Most of the radiological source term that can be expected to be released from the core to containment has already been released.  It is being held up inside hard containments and depleted via radioactive decay, plateout, etc.

The work now has to do with mitigation of the radiological source terms, from water injection into the reactor coolant system, water washdown of plant components, and so on.  If the semi-volatile fission products and alkali metals are in effluent, they will likely not re-evolve to the atmosphere in large quantities.  Most importantly, for now, the Spent Fuel Pools deserve attention, and hopefully the operators will be able to mitigate zirconium fire events in the pools.

And in Primer for Studying News Releases on the Japanese Reactor Accidents, I described how computer codes – including one that I have written – model fission product release as a function of temperature during fuel heatup.  Fuel melting doesn’t have to occur to release fission products.

On March 19th Glenn Reynolds linked an article at Pajamas Media that weighs in thusly:

Nature has also learned that initial CTBTO data suggest that a large meltdown at the Fukushima power plant has not yet occurred, although that assessment may change as more data flow in during the coming days. Lars-Erik De Geer, research director of the Swedish Defence Research Institute in Stockholm, which has access to the CTBTO data and uses it to provide the foreign ministry and other Swedish government departments with analyses, says that the data show high amounts of volatile radioactive isotopes, such as iodine and caesium, as well the noble gas xenon. But so far, the data show no high levels of the less volatile elements such as zirconium and barium that would signal that a large meltdown had taken place — elements that were released during the 1986 reactor explosion in Chernobyl in the Ukraine.

And today the AP acknowledges that the cores in Units 1, 2 and 3 are “partially melted.”  The Captain’s Journal is a week or so ahead of the rest of the nuclear experts.

Here is another prediction and technical explanation.  Power has been restored to the plant.

Japanese authorities have taken a major step in managing a nuclear crisis by connecting all six earthquake-damaged reactors to power supply, but it’s too soon to say the crisis has reached a turning point, experts said on Monday.

Power has been connected but not switched on to crank up most coolers and pumps, which may have been badly damaged in the quake and tsunami that on March 11 triggered the world’s worst nuclear accident since Chernobyl. Only one pump has been activated.

The damaged reactors and their spent fuel pools at the Fukushima Daiichi nuclear power plant, 240 km (150 miles) north of Tokyo, urgently need cooling from air-conditioners and from water pumped in.

U.S. Energy Secretary Steven Chu, asked by CNN whether the worst of Japan’s 10-day nuclear crisis was over, said: “Well, we believe so, but I don’t want to make a blanket statement.”

U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko added that radiation levels at the plant appeared to be falling.

But nuclear experts in the United States and elsewhere were not quite as positive.

“I am not sure if the crisis has passed but it is definitely a step in the right direction,” said Peter Hosemann, a professor at the University of California Berkeley’s Nuclear Engineering Department.

“It is getting better. However, we don’t know if the pipes and connections and pumps still work at this point or what works and what not. But having power makes external water supply easier.”

This is a positive step.  This is good.  This makes addressing the problems an order of magnitude easier.  But don’t hurry to a conclusion.  Water may have intruded into terminal cabinets, circuitry, pump motors, transformers, load centers and motor control centers, and getting power to the plant is not the same thing as getting power to individual components.  There will be ground faults, broken connections, flooded components, and breakers that trip open on over-current and under-voltage when they are closed.  It will be a massive headache for the operators.

This isn’t over.  The Japanese are performing heroically as I have observed.  They are improving the situation.  But habitability of land, edibility of crops, cleanup of the plant, and recovery operations for the rubblized reactor cores will take time and money.  Pray for the Japanese – and don’t jump to any conclusions from MSM reports, like the notion that the fact that Unit 3 contains mixed oxide fuel (MOX) makes it somehow more dangerous than UO2 cores.  Please don’t fall for the hype.  Fuel fines will not become aerosolized or airborne, and the Plutonium is part of a metal crystalline structure.  It will stay bound within the fuel matrix.