There was another documentary on NHK, "Close-up Gendai" #3400 http://www.nhk.or.jp/gendai/kiroku/detail02_3400_all.html
Here is something I did not grasp before. The frozen wall has to go all around the reactor buildings, including the sea side, in order to hold the groundwater in. If the water table drops too far, the water will leak out of the reactor buildings into the ocean. The ice wall should stop most groundwater coming downhill into the reactor area. That water will be taken from well into the "bypass" pipes and pumped into the ocean. If they did only that, it would dry out the land under the reactors, the water table would fall, and the water from the reactor basements would seep out into the ocean. This is shown in the video images here below the fishtank simulation of the frozen wall. Images 6, 7 and 8 here: http://www.nhk.or.jp/gendai/kiroku/detail02_3400_3.html - Jed
