Here is something more specific from the Nuclear Energy Institute,
http://resources.nei.org/documents/japan...Update.pdf

Quote:Sixty percent of the used fuel on site is stored in the shared pool, in a building separated from the reactor buildings; 34 percent of the used fuel is distributed between the six reactor fuel storage pools, and the remaining 6 percent is stored in the nine dry storage containers.

The used fuel pools at the Fukushima Daiichi reactors are located at the top of the reactor building for ease of handling during refueling operations.

The used fuel pools are designed so that the water in the pool cannot drain down as a result of damage to the piping or cooling systems. The pools do not have drains in the sides or the floor of the pool structure. The only way to rapidly drain down the pool is to have structural damage of the walls or the floor. As of mid-day March 15, there is no evidence to date that this has occurred.

I have seen some information questioning the statements from the US NRC.

Another point that I have heard is that using seawater to replenish the pools has its problems and canoot be used for a long time, in this case, they need fresh water (boronated). This may be the reason they are talking about fire canons, along with the probability that the helicopters will not be able to carry in enough water on their own to restore enough water to the pools.