Unit 1 Torus Investigation Nov 2013; Initial Findings
TEPCO has done an inspection of Unit 1’s torus room, this time with a floating robot boat. TEPCO released most of the first day findings for downcomers 1-4. On the second day around the other side they only released data for downcomers 5-6. Data for anything past downcomer 6 back around to downcomer 4 is not given in TEPCO’s reporting and is not in any of the videos. The area that has not been disclosed is also the area of the torus room that faces the doorway opening of the pedestal. This is the area most likely to experience a burn through of melted fuel. TEPCO needs to release all their data on their work immediately. Not doing so just adds to the growing distrust of the company and a horrible lack of public transparency.
Areas boxed in blue have been inspected and had the video released.
TEPCO claims all areas have been inspected but only released information and video for sections 1-6
Pedestal opening diagram
Estimate of melted fuel outflow potential in the pedestal
TEPCO found the drain pipe was broken at this section. These are pipes that siphon off condensation from the back side of the steel containment bulb and do not reach into containment itself. The number 1 downcomer drain pipe was leaking water in a steady stream. No residues or burning type damage was seen in this section.
Downcomers #2 and #3
Both of these were found intact and without any unusual nearby damage.
Water was found leaking around downcomer 4. Some appeared to be coming from areas in the ceiling region of the torus room. Evidence of other water leakage was seen closer to the downcomer. This downcomer also showed burned off paint in a pattern that flares out as it leads to the torus. The burned paint is clearly defined and offset more to one side. These structures are normally clean with the steel painted orange. There is also an excessive residue found below the number 4 downcomer on the torus, as can be seen in the photos below.
water seen running off the ledge below the number 4 downcomer
Number 4 downcomer
residue below the number 4 downcomer
The area below the number 5 downcomer shows clean concrete and an intact drain pipe.
The symmetrical scorching of the downcomer pipe seen on downcomer 4 is present here.
Larger amounts of scorched pipe were found here along with considerable residue on the torus tube. There was also a large number of bubbles coming up from the standing water below the boat. Also found is what appears to possibly be melted pipe below the water surface. There has been some reporting that this sand pocket drain pipe is made of PVC plastic. This has a low melting point of around 160C.
Number 6 downcomer
Bubbles seen underwater
Possible melted PVC pipe near downcomer 6 below the water
The two videos put out by TEPCO show the 1-4 downcomer on the first video and only two downcomers on the second video. TEPCO appears to report that they have completed all of the work yet no information about the areas between downcomers 7 – 8 and 8-4 has been made public.
Videos of the work:
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