Analysis: Unit 3 Mast In Pool Inspection
TEPCO released a new video and handout of the unit 3 mast that fell deeper into the spent fuel pool.
We have processed the video into about 200 still images that can be found here.
The full video of the inspection can be found on our Youtube channel.
TEPCO estimates one end of the mast landed along the east wall with the end resting on a control rod drive rack. The other end appears to be resting tangled in concrete and rebar debris on top of the fuel racks. Portions of the middle of the mast can be seen spanning above the fuel racks by a few inches. What appears to have been the structure that originally held the mast into the fuel crane can be seen partially down the mast.
What is of particular note in the findings from this inspection is that the control rods housed along the east (sea side) wall of the pool. These control rods have considerable damage,with one laying mangled under the mast. The control rods contain halfnium in a steel shell. This damage could have caused them to leak.
This diagram shows the structure of a normal control rod with cracks, an ongoing problem in reactor operation. CNIC has reported in the past about control rod cracking problems at Fukushima Daiichi
The severely bent control rods can be seen in this photo of the mast end as it rests on the control rod rack.
It is not clear if the mast caused this damage or if it was previous damage.
This shows the end of the mast as it sits on the control rod rack bottom lip.
The top end of the mast resting on a tangle of rebar and debris.
Telescoping section of the mast, a gap can be seen under the mast showing that it may not all be resting on the fuel racks.
Another section of the mast showing a gap between the mast and the debris on the fuel racks.
The additional understanding of the location of various structures in the spent fuel pool caused us to revisit the old heat images taken in March and April 2011. This showed the area of the fuel gate and the south wall facing unit 4 of the pool to be the hottest. The image below takes the heat image outline and overlays it on the pool map. The pool map rotated to match the heat map. More investigation is needed to determine if the reactor could have been contributing some of the pool heat via the fuel gate.
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