Have they determined where the sunken cores are at Fukushima?

[ElliotSmith]

After almost 4 years sine the triple meltdowns, have they determined the exact location of the corium at Fukushima reactors #1-3?

How far down has it burned through and has it breached the concrete base/foundations of the reactor buildings? Has it reached ground soil?

Also, how much progress has been made on the unloading of the spent fuel pools?

 

[Astronuc]

They would probably be looking on the pedestal underneath the pressure vessel, but inside primary containment.

See - http://sitn.hms.harvard.edu/wp-content/uploads/2011/06/nuke_fig2.jpg

The core debris is likely under the pressure vessel and possible some particulates are in the water in the bottom of containment and torus.

 

[ElliotSmith]

Do they know if the melted core material has burned through the concrete base of the reactor buildings and into the ground soil beneath?

How do they plan on (eventually) removing the big blob of corium sitting somewhere beneath the pressure vessel?

I know that in the three mile island defueling/decommissioning process, the melted core material was broken up and vacuumed out. But that was different because TMI reactor #2 only suffered a partial core meltdown and 100% of the core was still contained inside the reactor vessel.

 

[Astronuc]

As far as I know, TEPCO as not confirmed where the 'corium' is located, but I imagine they suspect in the bottom of the pressure vessel. Some of the core (fission products) obviously dissolved in the water that did find its way into the RPV. The fuel, cladding and core structural materials probably reacted (oxidized) in the coolant, and the reaction products would have flowed out with the water into the containment. TEPCO has to get a camera underneath the RPV to see if it was breached. The water there is highly contaminated with radionuclides, so the radiation affects the CCDs.