Fukushima unit #3 muon imaging update

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