nonfissionable

The pile feeds on slugs of Uranium-238, which is nonfissionable.

DA believed that the object's alchemical matter was nonferrous and nonfissionable.

He couldn't be certain that the planet's dense atmosphere wouldn't alter the flight of a nonfissionable missile, so he targeted it directly at an active volcano.

Moreover, USEC is hardly alone in the business of separating U-235 from nonfissionable isotopes of uranium.

Recent intelligence interest has centered on Iraq's efforts to obtain uranium raw stocks and in building a high-technology gas centrifuge plant for separating fissionable uranium 235 from nonfissionable uranium 238.

But plutonium poses far greater disposal problems because it is chemically distinct from nonfissionable materials, and can thus be separated out with less sophisticated technologies within the reach of, say, Libya or Iran.