For low-level wastes - as opposed to the high-level spent fuel that the department wants to bury at Yucca - the Energy Department is trying a new material, a polymer foam to bind up radioactive materials indefinitely.
But the big challenge is spent reactor fuel, which will remain intensely radioactive for centuries and has many components that policy-makers want to keep out of underground water for millennia.
The Energy Department's early plan was for ordinary steel, but it moved up to alloy22 for better corrosion resistance. But alloy 22 is harder to weld than ordinary carbon steel, and welds, experts say, are where failure most often occurs.
The department's plan is for a "drip shield" of titanium over each container. The containers would be 6 to 7 feet in diameter, and about 16 feet long, to be parked in a line, filling the tunnel like subway cars.
Nucon sees instead giant, elongated watermelons made of ceramic, 18 feet long,
with a wall 3 inches thick and an inner diameter of 5.5 feet. The ovoid shape is a way to reduce the risk of cracking the ceramic if it bangs into something; with rounded ends, the force of impact would be better distributed around the container.
Nucon believes it has made an important advance in being able to cast thick
ceramics. Making it thick is a challenge because cintering requires even heating and cooling, increasingly difficult in thick structures. This solution is a combination of conventional thermal heating, plus microwave energy, which heats evenly.
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