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.