Today's
Tepco Press handout of unit #3 muon imaging shows the possibility of
partial melt-through of the RPV. Tepco says as much as 50% of the corium
from the core area and bottom of the RPV may have escaped the RPV’s
bottom head. Of the 210 tons of fuel bundles (160 tons), control rods
(15 tone), and structural materials (35 tons) in the core before the
accident, there is only about 30 tons remaining. Where there was about
35 tons of control rod drive mechanisms in the bottom head before
3/11/11, about 90 tons of collected material is indicated by the muon
scan. This suggests that 125 tons of corium (admixed, formerly-molten
debris) may have exited the RPV bottom head. The
July 22nd
submersible robotic investigation showed considerable debris collected
inside the pedestal, but little or no compromise of both the RPV bottom
head and the Control Rod Drive Mechanisms that protrude from the bottom
head. It then seemed that much, if not most of the corium remains inside
the protruding CRDMs. However, the
9/29/17 Tepco Press handout indicates that all of that corium exited the RPV and is now collected in the bottom of the pedestal.
https://www4.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170928_01-e.pdf
Leslie Corrice
