It's now Sunday morning, and the situation in Japan continues to get worse by the hour. Clearly, as everyone is now universally admitting in the media, we are witnessing the greatest reactor accident since Chernobyl.
1. The Japanese government has now acknowledged that partial meltdowns have probably happened at the Fukushima plants. Previously, physicists had speculated that the core at Fukushima Daiichi I was partially melting due to the presence of cesium and iodine (which are byproducts of the fissioning process). Where there is smoke, there is fire. Now, its official. Also, 3 workers have come down with full blown radiation sickness, another indication of the intense radiation at the site.
2. At Unit 1, as an act of desperation, plant operator have been injecting seawater directly into the core of the reactor. This has never been done before in history. We are watching a science experiment. This will also most likely make it uneconomical to clean up the reactor afterwards (due to corrosion, contamination, etc.). The utility has probably decided to junk the reactor afterwards. (This scenario of flooding the core with sea water does not appear in standard nuclear engineering textbooks. We are entering uncharted territory.)
3. The accident has now spread to Unit 3, which also lost control of its emergency core cooling system (ECCS). This means we may see a repeat of the accident at Unit 1. We may also see a steam/hydrogen gas explosion which rips the containment apart. What could happen next? No one knows. But a meltdown takes place in stages. First, you have the core uncovered, temperatures soar to 5,000 F, melting begins, and cesium, strontium, iodine are released. Second, it takes 30 min. to several hours for the entire core itself to melt. At TMI, it took roughly 1 hour for 90% of the core to be damaged. Third, even after a complete core meltdown, it still takes a steam/hydrogen gas explosion to blow apart or crack the vessel (which contains the uranium) and the containment structure (which has already been severely damaged).
At present, it seems that Unit 1 has only suffered partial melting. The situation at Unit 1 is stable, but the situation with Unit 3 continues to worsen hour by hour. The danger is that a further secondary earthquake or pipe break could cause the sea water to flush out of the core, uncovering the uranium and initiating a full-scale meltdown.
More to come....