Japan nuclear crisis: Options are few to prevent Japan nuclear catastrophe - latimes.com: "Encasing the fuel rods in sand and concrete, furthermore, would trap heat and allow them to get much hotter than they are now, potentially enabling them to burn through the concrete and escape from their tomb.
Because the fuel rods and the reactors are so hot, the concrete would undergo a phenomenon called flash-set, in which it would solidify extremely rapidly.
But the result would be a material with a consistency much like gravel rather than stone.
'My gut feeling is, it's a bad idea,' Lewis said.
Officials at Japan's Nuclear and Industrial Safety Agency on Saturday said it was highly unlikely that workers could use massive amounts of sand or cement to smother the super-hot fuel inside the reactors or storage pools at the Daiichi plant any time in the near future.
'We believe it is not a realistic option,' said the agency's Hidehiko Nishiyama.
Teruaki Kobayashi of Tokyo Electric Power Co. said the company had not ruled out the entombment strategy. But he added that the possibility was remote unless conditions at the plant changed substantially — for instance, if the fuel rods caught fire and began spewing radioactive ash everywhere."