I'm not quite sure what your question is with the spent fuel pool. The water will just sit there and slowly evaporate probably or be cleaned and checked for contaminants before going elsewhere. It's really not that much water. I think you're making a problem where there isn't one.

The water keeps it from melting as the spent fuel becomes a little more inert each day (it transfers heat to the water, and as we know radioactive stuff has half lives). After a few years, we can move it to dry storage (incased by concrete and steel).