I have just seen a photograph of the used fuel pond at unit three.
To be blunt with you it is a mess, the pond has lots of rubbish in it from when the building was damaged. But it is important to note that it is impossible right now to say how much (if any) damage has occurred to the fuel in the pond.
I imagine that the additional objects (the rubbish) will make the clean up of the pond involve more work. I think that every bit of rubbish will need to be checked for contamination when it is pulled out of the pond. This could be a lot of extra work when compared with a nice tidy and clean pond like the one in unit four.