TEPCO Inspects Unit 2 Torus With Walking Robot

TEPCO did inspection work at Unit 2 in the torus with the Toshiba walker-bot (it doesn’t have a name apparently) and it’s little buddy robot.

The work involved inspecting the torus downcomer vent pipes. TEPCO specifically looked at the torus bellows joint, an area we have previously identified as a potential problem location within the reactors. They also inspected the sand cushion drain pipe. This is a small pipe that sits below the junction of the containment structure and the torus downcomer pipes. This is another area thought to be a weak point and prone to burn through by melted fuel.

TEPCO’s inspection of one downcomer did not show any damage to that specific structure but that may not have been the complete point of the effort. This is the first successful attempt to look beyond the easily accessible areas. Robots have previously been limited to the catwalks and concrete floor areas of the plant. The “mini-me” tethered robot was able to cross the torus pipe surface to look at the downcomer pipe.

Walker-bot and mini-me’s trip into the torus was not released on video in full. TEPCO so far has only released very short clips. The video clips are posted at the end of this article.

The photos and map of the work area showed limited damage and what looks like a water mark line fairly high inside the torus room indicating it had filled with water at some point.

TEPCO also mentions in the handout that there were obstacles on the torus catwalk preventing further inspection of other areas.
Handout: handouts_121211_01-e

The handout included these three images of the torus downcomer and the sand pocket drain pipe.

TEPCO did not pre-announce this work or explain further why they did this inspection. They did quietly admit a few weeks ago that they assume “fuel fragments” have made it into the suppression chamber (aka: the torus or torus room). This work may be the beginning of TEPCO’s effort to identify further what has happened in the torus area of the other two melted down reactors.

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