Fukushima Unit 1 Reactor Well Cover Dislodged

TEPCO showed in a handout that got little attention that the concrete reactor well cover for unit 1 is dislodged.

The concrete cover sits on top of the reactor containment cap to provide both radiation shielding and some level of blast shielding. TEPCO has admitted in the past that there is at least some leakage out the top of unit 1 but had not explicitly admitted the reactor well cover was dislodged. These covers are a series of concrete sections that layer down into the reactor well. The concrete cover for unit 3 was found to be in place but the center section was caved in. No additional details were available and they may need to remove all the debris to get a good idea exactly how damaged the concrete cover for unit 1 is. This does indicate that damage to the upper structures could be worse than initially thought.

 concrete cover diagram, 5 shows the layers of concrete well cover

u1_refueling_view_2014  TEPCO diagram showing where images were shot from, taken in Oct or Nov 2014 u1_view5_2014 View 5 image, lower blue arrow shows a layer of the concrete cover dislodged and raised up. The spent fuel pool and refueling crane are directly to the left.

u1_view6_2014  View 6, dislodged concrete cover to the right in this view.

The cover situation also hints that the spent fuel pool or the steel gate between the reactor and the fuel pool could have sustained more damage than initially assumed. Again, they will need to remove debris to determine this. Unit 1’s spent fuel pool had the least amount of fuel in it at the time of the disaster, with most of that being older fuel. Unit 1 has 392 assemblies in the spent fuel pool with 70 of those having some amount of pre-disaster damage.

TEPCO also plans to scan the unit 1 reactor well for heat signatures with an infrared camera as they proceed to remove more sections of the cover. This should give them some idea of additional damage in this area. Timing for that work is not mentioned.

TEPCO reported today that they would proceed with removal of more unit 1 cover roof sections over the next week.

Rough machine translation of the original TEPCO handout can be found here along with the images and diagrams in their original context
https://docs.google.com/presentation/d/1ESeqKxh5BljQ5ZsyEj-a0Is-u6_fjvj-1dafrQEVDTI/edit?usp=sharing

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