In the U.S., more than 75% of the radioactive waste at the nation's 104 commercial nuclear reactors sits in pools, according to the Nuclear Regulatory Commission. The rest is in dry storage casks.
The pools were intended as temporary rest stops before transport to a central location for reprocessing or disposal. With no such sites available, the used rods, have been placed closer together than planned and largely left in the pools.
While the NRC permits such packing, the TVA is considering a change.
"We're likely to do more dry-cask storage now," TVA spokesman Ray Golden said. Critics, including the Union of Concerned Scientists, say the pools are vulnerable and that the NRC should require the transfer to dry storage casks made of concrete and steel when the waste rods are cool enough, not when pools are nearly full.
The nuclear industry has hoped the federal government would build a long-term repository inside Yucca Mountain in Nevada, where nuclear waste from around the country could be held for hundreds of thousands of years. But the plan has encountered strong opposition.
http://www.usatoday.com/news/nation/environment/2011-04-11-nuclear-pools_N.htm