Why not just bury them?
The idea of smothering and sealing Japan's overheated nuclear reactors in sand or concrete to stop the crisis is appealing. But experts say that it's too early for something that desperate and that it could be a big mistake that could make matters worse.
Most urge continuing the current efforts to cool the radioactive material, and at least one suggested massive spraying to hold down radioactive dust.
Fires, explosions or partial meltdowns have struck four of the six reactor units at the Fukushima Dai-ichi power plant. There are few options for stopping the dangerous overheating of nuclear materials there. Military fire trucks sprayed tons of water Friday, and workers hope to restart cooling systems once a new power line is installed.
Reporters in Japan raised the notion Friday of sealing the reactors and fuel rods in concrete as an emergency measure. But officials with Japan's nuclear safety agency and the plant's operator did not embrace the idea.
"We believe it is not a realistic option," said Hidehiko Nishiyama of the Nuclear and Industrial Safety Agency. And Teruaki Kobayashi, a manager at the Tokyo Electric Power Co., said the utility would not rule out entombing the reactors but thinks the probability is low.
It's true that concrete tombs may someday stand at the troubled nuclear complex, one expert said, but only as a long-term strategy once the radiation has cooled.
The entombment idea has been touted on American television by Michio Kaku, a physics professor at the City College of New York and a television host on the Science Channel. He has talked about dumping a combination of boric acid to dampen the nuclear fission, sand and eventually concrete to seal off the nuclear material.
Such a massive effort would take days if not weeks to plan, so he argues preparation should start now in case it becomes necessary. He envisioned an armada of helicopters and workers to dump sand and then concrete to smother the spent-fuel pool and other damaged nuclear material.
But experts see risk. For one thing, the structures that confine the radioactivity now could be damaged if heavy loads of material are dumped on them, opening new avenues for the hazard to escape.
"When you drop tons of material from hundreds of feet in a helicopter, you're going to do some damage," said Alex Sich, a nuclear engineer at Franciscan University in Ohio. "It could be a bad idea. ... I would ask them to stop and think three times before they do any dumping of heavy materials."
Sich, who has lived in Chernobyl and published research on the disaster there, noted that Russian authorities dumped some 5,000 tons of sand, clay and other materials from helicopters in an attempt to smother that dangerous reactor.
The Japanese situation is different, he said. The Japanese reactors are surrounded by multiple barriers designed to contain radiation from the reactor cores. If a heavy dumping cracked the inner vessels and exposed the reactor cores, "that would be absurdity," he said.
Other risks focus on the spent fuel rods, which are a key source of concern. While pouring tons of sand on the rods would block radiation from escaping, it would also insulate them and make them heat up faster. The heat could decompose the concrete floor, allowing the rods to fall through, which could complicate efforts to contain the radiation, said Elmer Lewis of Northwestern University.
Sich suggested it might be better to spray the reactor with dust-suppressing materials from helicopters, as was done at Chernobyl. Dust is one way for radioactivity to spread great distances.
Maybe sprayers could be installed to continuously tamp down dust, he said, while acknowledging the installation would further expose workers to radiation.
Lewis, who has consulted frequently on nuclear reactor issues for U.S. national labs, said the time for concrete tombs might come once the radioactive materials have cooled -- a process that could take years.
At that point, it might prove too expensive to safely remove the building materials and bury them, he said. It might make more sense to cover the remains with concrete or some other material to seal in the lingering radiation, he said.
But as for now, he and others said, the idea of massive sand dumps looks too risky.
"If you thought all was lost, perhaps in that instance it might make sense," said Travis Knight, acting director of the nuclear engineering program at the University of South Carolina. "I don't see it coming to that at all."
David Lochbaum, nuclear safety director at the Union of Concerned Scientists and often a critic and watchdog on nuclear energy, also called the idea of sealing in the reactors or fuel pool something to be done "only when hope runs out."
And he believes there is still hope.
Mari Yamaguchi and Yuri Kageyama in Tokyo contributed to this story.