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.