On Saturday, April 10 TEPCO inserted IRID's nifty new shape-changing robot into the first floor level of containment in Daiichi unit-1 to inspect damage and maybe find the missing core. This was the same unit that was muon scanned last month by two units from the High Energy Accelerator Research Organization [KEK] in Tsukuba, Japan. The scanners revealed that there is no fuel in the reactor vessel, so it was hoped the robot could get all the way around the interior containment catwalk to take photos, video and readings on radiation levels and temperature. Unfortunately, the robot only made it 2/3 of the way around, and then it died.
Well, it didn't die completely, it just stopped taking commands from its operators and cannot move or change shape. For awhile there, it was still transmitting data.
According to an IRID official, the operators tugged on the robot's cable and sent instructions for it to change shape, but it still would not move. The robot's camera, dosimeter and temperature gauge were not damaged, and the robot was still capable of transmitting data.
Neither TEPCO nor IRID have released any of the inspection data so far, but there was apparently 'debris' in the area where the unit stopped moving. The
diagrams in this article show that to be in the vicinity of downcomers 6 and 7. TEPCO has never released photos or video from their boat robot inspection of the unit-1 torus room back in November of 2013 in the area of those downcomers either. If the molten corium managed to exit the pedestal - a round 'room' at the center of the containment directly beneath the reactor - it may have reached the downcomers and melted through.
If the bulk of the corium is not in the pedestal it cannot be removed from the top of the reactor well, and the radiation levels are far too high for humans to go into the containment or torus room to remove it from inconvenient locations. So obviously finding the corium is very important for planning future projects, even though the SFPs [Spent Fuel Pools] for units 1, 2 and 3 will all need to be emptied before any corium is tackled. That job will take some years, but not enough to make a difference in the radiation levels in the containment or anywhere close to the corium. Wherever it turns out to be.
IRID has developers working on robots they hope will be able to do the necessary inspections and mapping so that when the time to defuel comes they will have some idea of how to go about it. Operators cut the robot's cable and are abandoning the failed shape-changer in the containment.