Some background for our readers.  Fuel rods are removed from a reactor during the refueling process.  The old rods that are removed are referred to as spent fuel.  These rods, although no longer optimal for producing electricity in a reactor are still highly radioactive and filled with energy.  This spent fuel has long been the biggest problem in the electrical industry. For years the US has been struggling with the issue.  Yucca Mountain in Nevada is seen as one answer.  Basically hollow out a mountain in the desert in the State of Nevada.  Only the people of Nevada do not seem to be too impressed by this idea.  So for now the standard operating proceedure in the US and Japan is housing the spent fuel on the reactor sites.  These spent fuel pools contain water and are at least 40 feet deep.  The spent fuel rods are lowered into racks at the bottom.

Water is circulated and it requires approximately 8 feet of depth to contain the radioactivity.  There are some reports that the rods in these pools in Japan may be exposed.  Other reports say the experts think the water in these pools may be boiling as cool and piping systems are damaged or fail.  There is a massive amount of spent fuel stored at Fukushima.

In the US billionaire Bill Gates is amung the supporters of a technology to safely put this spent fuel to use generating electricity in a Traveling Wave Reactor.

http://www.terrapower.com/Home.aspx

For now though it is just one more huge problem that Japanese authorities have to contend with.  Our prayers are with Japan.