July 6, 2016
It can no longer be said that no-one knows where any of the F. Daiichi melted fuel is located. On June 30th, NHK World reported that the corium (formerly molten and re-solidified fuel core) for unit #2 is in the reactor’s (RPV) bottom head. (1) High-tech muon imaging for unit #2 included the bottom head, which was not possible with the earlier imaging for unit #1. NHK reports the still-in-process image now shows a “large, black shadow” inside the 8-inch thick steel bottom head of unit #2, strongly indicating that the corium was contained. No melt-through, if you will.
When the unit #1 imaging was reported, it made major headlines across Japan and many popular news outlets world-wide. This was because the image showed, not surprisingly, that the entire unit #1 core was gone. Where it ended up is still a matter of debate, though it is this reporter’s opinion that much, if not most of the corium remains pooled inside the unit #1 RPV bottom head. Unfortunately, the geometry of the scan for unit #1 could not include the bottom head of the RPV. So, the “nobody knows where it is” rhetoric was part-and-parcel to all news reports, continuing the uncertainty and doubt concepts historically common to reporting about nuclear power plants.
The new unit #2 discovery was reported by only one news outlet…NHK World. It is nowhere else to be found, neither inside nor outside Japan. We can be reasonably sure that if the unit #2 muon image showed the bottom head to be empty, it would have made headlines everywhere; especially in the Japanese press. But, with the exception of NHK World, the discovery of the contained corium hasn’t seen the journalistic light of day!
Finding the re-solidified mass in the bottom head of unit #2 literally dashes the “nobody knows” speculations to ashes. We can be assured that we know where the unit #2 fuel core ended up, at the very least. Further, the unit #2 discovery suggests that unit #3’s corium is also cooled and pooled inside its RPV bottom head.
According to operator records, Unit #2 fuel uncovery began at approx. 4:30pm on March 14, and remained in a deteriorating condition until 7:54pm. Operator records for unit #3 say fuel uncovery began at 4:15am on March 13, and recovery started at 9:25am. Even though unit #3’s core appears to have been uncovered for about 100 minutes more than with unit #2, it seems unlikely that unit #3 would have experienced complete melt-through of the bottom head. On the other hand, unit #1’s fuel core was probably uncovered for more than 10 hours. Also, with core uncovery beginning about six hours after automatic shutdown (SCRAM), unit #1 had a higher decay heat rate than both units #2 and #3. Thus, the unit #1 notion of bottom head melt-through remains possible.
Finding the fuel core of unit #2 remaining inside its RPV, verifies one of this reporter’s assertions late in 2012. (See – “Fukushima Melt-throughs: Fact or Fiction”) I said that there was no way that unit #2 experienced a bottom head melt-through, and likely the same for unit #3. My 2012 prediction that unit #2 suffered a partial meltdown similar to Three Mile Island now seems incorrect. Unit #2 appears to have experienced a full meltdown. The same probably occurred with unit #3, but with no melt-through.
The point is that any further speculation of bottom head melt-through for F. Daiichi unit #2 must be ignored. The Muon imaging proves that it did not happen. Further, speculation of a unit #3 bottom head melt-through must be considered questionable.
Finding the mass of re-solidified corium with the Muon scan of unit #2 is the most significant news to come out of F. Daiichi this year. But, there has been an utter lack of Press attention given to the locating of unit #2’s corium. It clearly demonstrates that the only “newsworthy” information is that which keeps Fukushima fear, uncertainty, and doubt (FUD) alive. Once again, some “good news” concerning F. Daiichi is intentionally ignored by the world’s news media.