Saturday, March 12, 2011
This is a very large and powerful explosion. The sources in Japan claim it was a steam explosion. Either way it looks massive indeed. And considering the proximity to the core, alarming.
It looks very bad for nuclear power if an advanced nation, using some of the best nuclear technology, loses a plant and has several other cooling problems after an earthquake. Odds are there will not be a large radioactive release and the danger is not as high as most would think. Indeed the greatest risk is probably panic. But all the same, these plants must have been designed with large earthquakes in mind. Hopefully they can cool the cores properly and also prevent any further explosions. It looks as if the emergency cooling generators, a typical part of any nuclear plant, failed at the Daiichi plant. Chernobyl occurred during a test to see if the emergency generators there could be given enough time to turn on and gain full speed (a minute or so) by using the power generating turbine system as it spooled down. That did not work out, largely due to a cascade of human errors. In this case, it is important to see why these generators failed. I personally wonder about building plants at locations where there can be a passive emergency cooling system. A large water tower is not enough in this instance, but perhaps a small gravity fed reservoir serving the reactor cores via a shock-mounted pipeline or hose system?
"An explosion at a nuclear power plant in northern Japan on Saturday blew the roof off one building, brought down walls and caused a radiation leak of unspecified proportions, Japanese officials said, after Friday’s huge earthquake caused critical failures in the plant’s cooling system.
The Fukushima nuclear power plant before and after a reported explosion that affected a building at the bottom, left on Saturday. Television images showed a huge cloud of white-gray smoke from the explosion. Soon afterward, government officials said an evacuation zone around the plant had been doubled, to 12 miles.
The chief cabinet secretary, Yukio Edano, confirmed earlier news reports of an explosion at the Fukishima Daiichi nuclear plant, 15o miles north of Tokyo, saying: “We are looking into the cause and the situation and we’ll make that public when we have further information.” He was speaking amid fears that a disastrous meltdown could be imminent after critical cooling failures at that plant and another nearby, Daini, after both were shut down.
Images on Japanese television showed that the walls of one building had crumbled, leaving only a skeletal metal frame standing with smoke billowing from the plant. The Associated Press reported that the damaged building housed a nuclear reactor, though that report was not immediately verified by nuclear officials. The cause of the explosion was unclear, with some experts speculating that it may have resulted from a hydrogen build-up."
The plant is now cooling on battery tertiary backup power, good enough for a few hours. Hopefully this will buy enough time for sufficient cooling or to get the generators working again. If the core overheats and runs dry (all coolant boils off), there is a good chance that even so long after the scram, the fuel system can melt. If fuel elements melt and slump together, reactivity can increase. A super-prompt critical condition is highly unlikely, but possible. And then you have your disaster.