Anyway for those that want to continue the somewhat maddening quest to squeeze fresh speculation out of existing photos, I really do recommend those Oyster Creek plans that were linked to on this thread in the past.
Specifically as it relates to the present unit 4 speculation, try page 23 of the following document:
http://adamswebsearch2.nrc.gov/IDMWS/ViewDocByAccession.asp?AccessionNumber=ML011270300
Using the spent fuel pool & reactor locations to orientate ourselves with this plan of another plant and unit 4 at fukushima, the area at the top right of this drawing is the area of interest. Note 'personnel access enclosure', and cable tray bridges that are also said to be in this area. Also see location of spent fuel pool pumps, and further to the left some fuel pool heat exchangers. Also round the corner on the next side of the reactor building there are augmented pumps and heat exchangers for the fuel pool.
Now clearly there are dangers with using the plans for a different reactor but many of the things that are likely the same or different compared to Fukushima are fairly easy to identify. The most noticeable differences are that at oyster creek the dryer separator pool is oriented differently, and the equipment hatch & truck entry tunnel is on the left rather than the right side of the building. But many other features seem very similar, crucially the location of the reactor and spent fuel pool seeming like a good match, make it far too tempting for me to resist using these docs.
Anyway based on these docs Id say we could easily be seeing 2 different things going on at that location at reactor 4. A door. A shadow cast by the cable tray bridges. And maybe a 3rd option, green tarpaulin covering some sort of equipment at some point.
At this point the vehicle that is shown some way inside the unit 4 vehicle tunnel on some photos but is missing from other pictures interests me as much if not more.
And its the fuel pool itself that still interests me most. I wonder things like 'does the skimmer surge tank still exist at unit 4?'. And whether the pools got more damaged by subsequent quakes, whether there has been a change in leak rate or boil rate. When TEPCOs roadmap was published and included mention of putting a supporting structure under unit 4's pool, I felt reporters have failed us by not dwelling on this or asking more questions. And it was certainly interesting that news that they were going to spray water in more cautiously came out days later, but collided badly with events on the ground which were taking quite the opposite turn, with far more water having been sprayed of late, not less, to deal with high temperature they measured and then acted almost surprised about (surprised, really?) Any of the other pools could yet tell a story too.
