TEPCO has investigated the torus room of unit 1 with the new boat robot. This was an effort to look closely at the downcomer pipes that run to the torus and the related structures. They did find leaks at two locations on the first half of the investigation. One is a leak that appears to be near the ceiling and at other locations around downcomer 4 and a broken and leaking sand pocket drain pipe near downcomer 1. They also found the collection pipe between downcomers 1 and 2 to be broken.
TEPCO has conducted investigation around the other side of the torus room but hasn’t provided any detail yet.
Radiation levels near downcomer 4 were the highest found on this inspection.
2.99 Sv was found adjacent to downcomer 4 with levels around 2.46 Sv below the downcomer.
One side of the downcomer appears charred with the paint burned off and the other with paint intact as can be seen in the photo above. Water is dripping down from somewhere above the downcomer. This was rather unexpected when you look at the area.
This shows a closer look at the #4 downcomer and the transition between the charred looking downcomer and paint transition.
Also beside this downcomer, near where water is leaking from above is a curious section of concrete wall as seen below.
The textured surface with what appears to be some sort of residue is not found on the other sections of the concrete wall on the initial inspection. This could be corium residue or some sort of build up from the water flow. The area reads at almost 3 Sv.
This close up of the wall shows the residue in detail. It appears somewhat black rather than rusty as is seen on the torus tube in the same area.
Near downcomer 1, the drain pipe is severed and draining water out of the sand pocket area. The ring pipe is severed between downcomers 1 and 2. This indicates damage but isn’t clear how it was damaged. It does show a leak path for water out of containment.
Also of note is another downcomer location, notice the water running down the concrete wall and the absence of residue on the concrete wall that was seen near downcomer 4.
We will have more reporting after TEPCO releases the results of sections 5-8. Right now the conditions around downcomer 4 are highly suspect but do fit into some expectations based on previous data. This may be a leak point where corium escaped containment but that is not fully confirmed yet.
TEPCO report on the first inspection with the boat robot in English:
TEPCO report of 2nd days work (machine translated)
Our gallery of enhanced images of this work:
TEPCO video of the first inspection:
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