Christopher Jon Bjerknes
In those tanks of the failed reactors and cooling ponds at Daiichi which cannot be returned to normal cooling functions, there is perhaps a far safer and more sustainable method of cooling the system than simply flooding it. I propose that a moderator fluid be poured into the tanks and that a separate self-contained system into which cooling fluid or gasses can be circulated also be placed in the tanks to cool the moderator and radioactive materials.
In this manner, the fluid which contacts the radioactive materials can be a moderator and remain in place without circulating outside the tanks, or being dumped into the ocean. This fluid can then be cooled with a separate system of a heat exchanger in the tanks, and piping to outside radiators and condensers, which separate cooling system would contain its own fluids or gasses which coolants never mix with the moderator fluid.
The old, failed circulation systems would in this way no longer be needed and the release of radioactive materials into the surrounding environment would be minimized.