Unit 3 Daiichi Pool Accident Analysis

TEPCO announced this week that the 1.5 ton mast for the refueling crane fell into the pool and sank as they tried to remove debris from the pool. TEPCO has done some testing of radiation levels near the pool and does not think there was fuel damage based on not finding drastically elevated levels.

The mast falling could create a couple of potential damage situations. It could fall and damage the fuel assemblies held in the pool. It could also damage or puncture the spent fuel pool metal liner causing a leak in the pool. The condition of the liner or the concrete pool has not been confirmed by TEPCO to date.

The mast that fell looks like this under normal conditions. It has minimal connections to the refueling crane.

TEPCO released these photos of the pool work showing where the crane is, the debris being removed and relative location. We have oriented all photo so that the sea side wall with the remaining bits of wall frame are at the top of each photo.



Taking the marked up photo TEPCO provided that circled the location of the mast and doing a rough overlay with a map of the spent fuel pool you can see a rough idea of where the mast fell. It appears to have fallen into the space left open for fuel handling. It could have nicked the nearby fuel rack but that would depend on how it fell once it began to sink. We can tell how and approximately where it fell. It is unclear what the mast did as it fell to the deeper depths of the pool.


The red and green landmarks provide points of reference for other photos of the pool that show the mast falling.

The purple circle is the mast as it falls and sinks.

These are the video stills of the mast in the original location and the progression as it falls and sinks.

The full video of the event can be found on our youtube channel

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