Soon to be widely reported and today in Asahi news there was evidently a fourth meltdown at Fukushima, on March 21. The fuel in Unit One had been cooled, but then things got out of control again. There were significant radiation releases to the environment (which we discussed at length here at FDL at the time, in comments) which were attributed to the first big rain after the first phase of the accident. [UPDATE: TEPCO is now contesting this interpretation of the data, so the story is still developing.]
This is a really big deal! The rises in radiation on March 21 were visible on monitors in Tokyo and elsewhere — I remember following them. It remains to be seen how much of the contamination of the environment outside the plant itself came from this fourth meltdown. Coupled with the front page NYT article blasting the Japanese government’s handling of the knowledge they had of the radioactive plumes, it is clear that the Fukushima accident is continuing AND continuing to have strong repercussions.
I strongly recommend reading this Asahi article. Here is a quote:
Between 1 a.m. and 3 a.m. on March 21, the pressure within the pressure vessel of the No. 3 reactor core increased sharply to about 110 atmospheres, likely caused by an explosion within the pressure vessel due to a lack of cooling of the fuel. That was probably the start of the second meltdown, Tanabe said.
As for the sudden pressure increase, Tanabe points to the possibility that the clump of melted fuel in the pressure vessel may have fallen apart due to a lack of cooling. The magma-like substance with high temperatures may have leaked out of the vessel and emitted large amounts of steam when it came in contact with water.
At the No. 3 reactor building, black smoke spewed from the reactor building on the afternoons of March 21 and March 23. Tanabe said the smoke may have been the result of what is referred to as a core-concrete reaction, when melted fuel comes in contact with the concrete of the containment vessel. Such a reaction typically occurs when insufficient cooling follows a core meltdown.
[At the time,] TEPCO officials said the black smoke was probably caused by rubber or lubricant oil catching fire.
It would be interesting to go back to what was being reported on March 22-23. I’m sure there were lots of articles saying the accident was over, nothing to see here, etc. Sort of like today…