Thing they are required by law to have some type of containment around the Spent Fuel Rod Pools. Cannot just put one in a barn.
The spent reactor storage pool was never intended as far as I know for long therm storage before they fuel could be put into dry storage. It is a pool to put fuel into temporarily when doing a refueling outage. Why TEPCO placed spent fuel in there and kept it there while reactors were running is a mystery to me. They have obviously decided to increase this storage area for long term use.
I was not suggesting the use of a pole barn. I said that in jest because the building was being used for a purpose it was not designed to perform.