The Nuclear Regulatory Commission has essentially accepted the industry's rationale on the safety of dense-packing fuel rods. Over the last two decades, the agency has repeatedly approved license applications by utilities to pack more rods into the pools.
Nuclear safety experts say that plants have packed up to five times more spent fuel rods than the pools were designed to store, though Nuclear Energy Institute officials say the pools contain no more than twice their original capacity.
The only advantage to keeping the pools packed so tightly is the cost of the dry casks, which would run about $5 billion to $10 billion nationwide, said Frank N. von Hippel, a Princeton University physicist who first disclosed the problem in a paper he co-wrote in 2003. He said he considers fixing the fuel pool problem one of the most important steps toward making U.S. nuclear plants safer.
"It is such a huge risk that it is worth the cost," he said. "We may not be as lucky as the Japanese were to have the wind blowing the radioactive emissions out to sea."
The reason so much waste has built up is the failure of the Energy Department to hold to its decades-old pledge to take ownership of it, triggering multibillion-dollar law suits by utilities against the government.
Under federal law, the waste was supposed to go to a repository at Yucca Mountain, about 100 miles north of Las Vegas. President George W. Bush approved the plan in 2002. But President Obama has taken steps to kill the plan, saying he wants to find a different site.
Energy Secretary Steven Chu warned last week that it could be decades before any permanent solution for the waste is developed, so the heavily packed fuel pools will be around for a long time.
"The utilities say that even if an accident happens here, they can deal with it," said Lyman of the Union of Concerned Scientists. But, he said, the Fukushima accident shows that some events will be difficult to anticipate and plan for.
"The Japanese have run out of pages of their operating manual, and they are just making things up," he said.